18 ms·

The scientific “unit” we call the decibel

• smat 1y ago
  Great post, the fusion of scale with unit is a mess. When using it as a factor, for example when describing attenuation or amplification it is fine and can be used similar to percent. Though the author is right - it would be even more elegant to use scientific notation like 1e-4 in this case. For using it as a unit it would really help to have a common notation for the reference quantity (e.g. 1mW). But I guess there is no way to change it now that they are established since decades in the way the author describes.
  • rocqua 1y ago
    Scientific notation would be worse, because you can't add them to get the combined gain. That's where dB's really shine.
• rebolek 1y ago
  While the author is technically right, I must argue that in the area of sound work, decibels make sense. Zero is base level, -3db is half loudness, +3dB is double. There may be a better way to describe loudness, but decibel is good enough.
  • readthenotes1 1y ago
    So on my amplifier, 0db is the loudest and -50db, where I usually listen is what? -47db is definitely not twice as loud as -50db, of course.
    • hgo 1y ago
      I'm not confident in what I'm saying here, so please correct me if I'm wrong as I'd like to learn: Human hearing isn't linear in terms of loudness. So a 3db increase in loudness sounds like "an increase", but the pressure is actually double. Hence, it makes sense to use db to describe loudness even in the context of perceived loudness to human-hearing. This is similar to brightness. In photography, "stops" are used to measure brightness. One stop brighter is technically twice the light, but to the human eye, it just looks "somewhat brighter", as human brightness appreciation is logarithmic, just like "stops" and "db".
      • deleted 1y ago
        [deleted]
    • bloppe 1y ago
      I mean, it should be, unless your amplifier is taking its own liberties with the definition of dB.
    • rebolek 1y ago
      Again, technically, it is. But ear isn't scientific device, neither is your amplifier. What I was describing is more than an agreement than some precise measurement. 3dB is more or less double the volume but different frequencies have different responses so I really wouldn't want to have some "perfect" way of measuring loudness as it would be so needlessly complicated that it would be useless.
    • timewizard 1y ago
      Human hearing perception response is logarithmic. This is part of the reason we use the unit. Our senses naturally work in that domain.
      • coldtea 1y ago
        > Human hearing perception response is logarithmic. It is, but -50db to -47db (+3db) is not double perceived loudness. It's double power. About +6 or even +10db would be double perceived loudness.
        • hashhar 1y ago
          Going from -50dB to -44dB is a much louder change than going from -6dB to 0dB. Human hearing is logarithmic. The dB is measuring ratio of sound pressure level and it's accurate that +/-3dB is almost doubling/halving of the SPL.
          • davrosthedalek 1y ago
            That doesn't make sense. -50dB to -44dB and -6dB to 0dB is the same change in power, as a factor. If human hearing is logarithmic, the same factor produces the same increase in loudness.
    • masklinn 1y ago
      3dB is “twice as loud” in that it’s twice (or half) as much power. Part of the reason why the bel is used is that human perception is closer to logarithmic than linear (weber-fechner law), so a logarithmic scale is a better approximation of “loudness” than a linear one.
    • coldtea 1y ago
      -47db is double the power. Perceived double loudness would be ~ -40db
    • relaxing 1y ago
      You should have a legitimate question as to what dB’s the amp is referring to. What brand and model is it? First, is it actually specified as dB’s? Most amps I’ve seen display volume on an arbitrary scale, no units specified. Second, the amp has no way to know dB sound pressure, as that depends on the rest of signal chain. So is the displayed figure referring to dBu, dB mV, something else, or something totally bunk?
      • davrosthedalek 1y ago
        If 0 dB is its maximum, then -50dB is 50 dB down in power from its maximum (so 10^-5). No m V or other post-fix needed.
        • relaxing 1y ago
          That’s true but not that helpful for determining what your ears actually hear.
          • creeble 1y ago
            For music, they hear about 10dB is half/twice as loud.
            • relaxing 1y ago
              That’s true but not really helpful for understanding what the amplifier is reading (thanks to nonlinearities down the line.)
    • djaychela 1y ago
      As someone else alluded to, 3dB is a doubling in power, not perceived loudness. 10dB will be perceived as a doubling in loudness. This is the original unit (the Bel, rather than deciBel) which was I believe derived by testing on human subjects to measure this. TBH I don't agree with a lot of the article - yes, dB on its own only indicates a ratio, but certainly in the field I work with this is known, and there are qualifiers (dBA, dbFS dbU) which tie the ratio to a known value so you're talking about an absolute, known quantity - even the dBa which is mentioned as if it comes out of nowhere is something which most audio engineers know about and use regularly because it's important to know the difference betweent he signal present and perception of it by the listener.
  • svara 1y ago
    For practical day to day use in very narrow context, yes. But, what you're saying is only approximately correct (the factor is a bit less than 2) and there are many related fields, even in areas that would be relevant to the physics of sound reproduction, in which the same notation "dB" means something different.
  • ajuc 1y ago
    > -3db is half loudness, +3dB is double It isn't tho. It's close but not exactly. And there's nothing about -3 behing half that makes sense except for familiarity (and it's not even wide-spread familiarity - most people wouldn't know how much louder +3dB is). It's just an unnecesarilly confusing definition that stuck for historic reasons.
    • danadam 1y ago
      > It isn't tho. It's close but not exactly. It isn't tho :-). It's not close to double loudness. It's double power, which is 1.41 higher sound pressure, which is only slightly louder.
  • kazinator 1y ago
    But, no! -3dB is half power, not half loudness. -3dB down is just slightly less loud.
    • globular-toast 1y ago
      Exactly. There's no way +3dB is perceptibly twice as loud. That's easy to test for yourself. +10dB is roughly twice as loud.
      • creeble 1y ago
        The BBC used to teach +6dB for twice as loud for music sources, but they've always been a bit conservative.
      • kazinator 1y ago
        +10dB is twice of something: it is an increase in loudness which is twice compared to a +5 dB increase. If +10dB is absolutely twice as loud, it means that 110 dB is 32 times as loud as 60 dB. We are then essentially denying that perception of loudness is logarithmic!
  • Sharlin 1y ago
    > -3db is half loudness Sure, perfect sense.
    • verzali 1y ago
      10*log10(0.5) = -3 That's the math of it.
      • Sharlin 1y ago
        I know. Well, ≈ -3, anyway.
  • rocqua 1y ago
    That's great, but only if 'Base level' is clear to everyone involved. Besides the base level, you also need to define what exactly you are measuring. Including the frequency weighting. This makes a spec sheet that says "this machine produces X dB of sound" effectively useless.
    • davrosthedalek 1y ago
      Any reasonable spec sheet would not say that. I say reasonable, because in the audio world, people pay extra money for oxygen-free copper cables.
      • rocqua 1y ago
        I'm looking at quite a few consumer level workshop machines. All of them have horrible spec sheets already. But on sound, even if they do mention it, it is still useless.
• ziofill 1y ago
  The nice thing about dBs is that they are logarithms: successive applications of gain/attenuation are easily computed by just adding up the dBs. (but yes, I agree that there should be more consistency in their definition)
• xnx 1y ago
  Weird that the author makes no mention of Sones: https://en.wikipedia.org/wiki/Sone https://en.wikipedia.org/wiki/Sone
  • itchingsphynx 1y ago
    Nor phons! “The phon is a logarithmic unit of loudness level for tones and complex sounds.” https://en.wikipedia.org/wiki/Phon https://en.wikipedia.org/wiki/Phon
• svara 1y ago
  A pet peeve I share! An expanded version of this article should become the article on decibels on Wikipedia. I've read that article many times over my life and for the first couple times came back thinking I was too dim to understand. Transparently leading it with "Here's something ridiculously overcomplicated that makes no sense whatsoever..." wouldn't fit Wikipedia's serious voice but actually be pedagogically very helpful.
  • esperent 1y ago
    There's often a Criticism of... section in Wikipedia pages. Maybe this blog post could work as a source, although it would be better to find something more established.
• timewizard 1y ago
  > That said, I don’t know how to pronounce “3e5” "Three to the exponent of five." Or "Three Exponent Five." Or "Three Exp Five." > Seeing this, some madman decided that 1 bel should always describe a 10× increase in power, even if it’s applied to another base unit. This means that if you’re talking about watts, +1 bel is an increase of 10×; but if you’re talking about volts, it’s an increase of √10× This is power vs. amplitude. This is the specific reason the dB is so useful in these systems. > the value is meaningless unless we know the base unit and the reference point No you just need to know if you have a power or a root-power quantity. Which should generally be obvious. https://en.wikipedia.org/wiki/Power,_root-power,_and_field_quantities https://en.wikipedia.org/wiki/Power,_root-power,_and_field_q...
  • ggm 1y ago
    > No you just need to know if you have a power or a root-power quantity. Which should generally be obvious. There has to be a Yogi Berra witticism about obvious things. Suffice to say fools like me work unadvisedly in spaces where this kind of axiom isn't obvious, because we're simpletons.
  • bigiain 1y ago
    > > That said, I don’t know how to pronounce “3e5” > "Three to the exponent of five." Or "Three Exponent Five." Or "Three Exp Five." Somehow, you need to distinguish between 3^5 (=243), 3 x e^5 (=~445.24), and 3 x 10^5 (=300,000). I'd pronounce "3e5" and "three times ten to the 5" in most cases.
    • deleted 1y ago
      [deleted]
    • timewizard 1y ago
      > 3^5 (=243) Three to the power of five. > 3 x e^5 Three times the fifth power of e. Or Three times e's fifth power. > 3 x 10^5 (=300,000). Three to the exponent of five. A calculator user once suggested "decapower." I think exponent and "EXP" are comfortable and easy to say and are ingrained to most old school calculator users. Which is also why I think "e's fifth power" can be a more natural sequence.
• ggm 1y ago
  Do a deep dive into audio vu Meters and how they got calibrated. Without being 100% sure, it's basically a totally subjective model, where back in the 1920s the BBC and some US company decided to assert "like us" and two models persist which have been retconned into some BIPM acceptable ground truth but it basically was "test it against the one we made which works" The hysteresis in the coil-magnet meter response turned out to be a feature, not a bug.
• formerly_proven 1y ago
  Decibels make sense and it’s usually only laymen who use only „dB“. I’d be surprised if you’d find „-45 dB“ as the specification for a microphone. Here’s two random examples: Sensitivity at 1 kHz into 1 kohm: 23 mV/Pa ≙ –32.5 dBV ± 1 dB Sensitivity: -56 dBV/Pa (1.85 mV)
  • nothacking_ 1y ago
    Except finding '-45 dB' is frustratingly common. Have a look at this random microphone datasheet from DigiKey: https://www.sameskydevices.com/product/resource/cmm-3125at-42316-tr.pdf https://www.sameskydevices.com/product/resource/cmm-3125at-4... They do state the test conditions "at 94 dB SPL, 1 kHz", but don't specify the units attacked to the actually measurement. It's given as a ratio to an unspecified quantity.
    • formerly_proven 1y ago
      Thanks, it's a good example for this bad practice. Especially because this could reasonably be both dBu and dBV, so it's actually ambiguous. (On the other hand with that tolerance the difference between the two is not that significant)
• hock_ads_ad_hoc 1y ago
  The author seems confused. Decibels aren’t units. They’re a way to express a ratio between a reference value and some other value. They’re used where they are useful.
  • coolcase 1y ago
    They are units too. When you have regulations relating to sound they will say how many dB the limit is.
    • formerly_proven 1y ago
      I've never seen dB being used like that in anything remotely official.
      • coolcase 1y ago
        https://www.osha.gov/noise https://www.osha.gov/noise Maybe the reference is implied though?
        • formerly_proven 1y ago
          That's hilarious, though they do seem to get it right on the other, more in-depth pages.
          • throwaway290 1y ago
            Yep, the NIOSH meter app they recommend uses dB(A).
            • radiowave 1y ago
              Though that's still incomplete, because (more of the context stuff that you just have to know already) the "A" here refers to the frequency-weighting scheme used in the measurement, and not to the reference level (which is SPL). It should probably be given as: dB(A) SPL, or dB SPL (A-weighted).
• atoav 1y ago
  But dB is not a unit, it is a multiplier. dB on its own is unitless and if we say "X is reduced by 6 dB" you know that the value of X is half of what it was before (×0.5) if something is amplified by 6 dB it is double of what it was before (×2.0)¹ Note that the unit only starts to play a role when you reference your dB value to some absolute maximum, e.g.: dBV which is referenced to 1V RMS dBu which is referenced to 0.775V RMS (1mW into a typical audio system impedance of 600 Ohms) dBFS which is referenced to a digital audio maximum level (0dBFS) beyond which your numeric range would clip (meaning all practical values will be negative) dBSPL which is refrenced to the Sound Pressure Level that is at the lower edge of hearing (0 dBSPL), this is what people mean when they say the engine of a starting airplane is 120dB loud Now dB is extremely useful in all fields where your values span extremely big ranges, like in audio engineering, where the ratio between high and low values can easily have a ratio of 1:10 Millions. So unless you want people to count zeroes behind the comma, dB is the way to go. When we think about the connection between analog and digital audio dB is useful because despite you having volts on the one side and bits on the other side a 6dB change on one side translates to a 6dB change on the other, the reference has just changed. If we had no dB we would have to do conversions constantly. Going from multiplier x to dB: 20×log₁₀(x) Going from dB to multiplier x: 10^(x/20) If you use dB to describe the power of a signal that is slightly different (you use 10 instead of 20 as multiplier/divisor) But you can see, dB is just a way to describe a unreferenced size change in a uniform way or to describe a referenced ratio. And then it would be good to know what that reference is. So if someone says a thing has 40dB you they forgot to tell you the unit. ¹ this is true for the amplitude of a signal and differs when we talk about the power of a signal, where 3dB is a doubling/halving.
  • rocqua 1y ago
    > But dB is not a unit, it is a multiplier. dB on its own is unitless. The point of the article is exactly that this should be the case. But it ends up not being the case. Mostly because people use dB with reference to some assumed baseline. But also because a 20db change could be a 10x change conpared to baseline, or a 100x change compared to baseline, depending on what unit you are measuring in.
    • 1y ago
• neepi 1y ago
  [flagged]
  • eru 1y ago
    Obviously there are better ways. The author mentioned several. Eg you could clean up the naming of the variants of the unit, and make it no less useful for RF work, and strictly better in general.
    • neepi 1y ago
      Sorry but no. Absolutely no one cares about the mathematical purity of a unit like the decibel. It's a hammer that turns log stuff into easy to work with linear stuff. It's x10 because that turns into reasonably easy to use numbers with enough precision to use casually. Otherwise it's just a log ratio. Any suffix is a log ratio to a reference value for the entire system (dBv / dBm etc). Say in a 50 ohm system I have an level 7 mixer then I need 7dBm into the port. My oscillator kicks out 0dBm (1mW). Then I need a 7dB gain block. I go to the datasheet for the MMIC and pick out a bias network that gives me around 7dB. I grab a eval board for the MMIC, solder the resistors on it, shove this on my VNA and throw 0dBm in one end and see if 7dBm comes out of the other end at the frequency I need. It's like Laplace. Do you really want to spend hours doing calculus? Source: actual electrical engineer, not some clueless hobby blogger. I really wish people would stop writing authoritative sounding articles on stuff they clearly have little experience with.
      • Dylan16807 1y ago
        They're not complaining about the basic nature of it being a log ratio to a reference value. Your use case would be pretty much the same if all the contradictory and confusing details of decibel were smoothed out. Source: I'm pretty sure I understand the actual complaint better than you do, and you're being dismissive of something nobody said.
      • rocqua 1y ago
        Have you considered the world outside of your expertise? Or the legibility of your field to people adjacent to it? dBs work well for RF once people get used to a few quirks. The problem arises when it gets applied to other fields as units, or when people from adjacent fields want to cooperate with people from the RF field.
• thrdbndndn 1y ago
  > this is in the same tradition that prompted us to name the “wat” in honor of James Watt. The unit is Watt, not Wat.
  • ahofmann 1y ago
    I'm sorry, that you missed the hilarious joke! For reference: https://www.destroyallsoftware.com/talks/wat https://www.destroyallsoftware.com/talks/wat
    • deleted 1y ago
      [deleted]
    • thrdbndndn 1y ago
      Ahh, I get the joke now. Good one :) As for the reason, if I have to guess, is because "decibel" looks better than "decibell". (Keep in mind decibel was actually renamed from the previous unit called "Transmission Unit" and was meant to be used as the main unit even at the beginning. "bel" was simply derived/implied from it, not the other way around).
  • kazinator 1y ago
    Whoosh ...
  • reichstein 1y ago
    Your irony detector may need calibration. Or mine does.
• kristjank 1y ago
  This seems exceedingly ignorant of the work decibels do in telecommunications, RF and fibre engineering. The voltage vs power relationship is something that exists and is a core memory of beginner blunders in the field, but it boils down to a simple 10 vs 20 division operation. Besides that, the decibel simplifies a lot of multiplying very small and very big numbers to summing of two-digit numbers that you can do in your head, and still preserve a big degree of accuracy. Whining about it makes me really doubt that the OP has any practical experience about the things they're talking about.
  • neepi 1y ago
    [flagged]
    • fouronnes3 1y ago
      However you must concede that the perspective of an outsider can be refreshingly eye opening sometimes, even to experts. Especially when it reveals the arcane practices that make a field difficult to learn - for example here the point about the base being too implicit is very valid. The article is perhaps ignorant of a few things, but its criticism shouldn't be dismissed outright IMO. Accepting constructive criticism from someone less experienced at something is a good exercise in humility, and can often help you improve. It's far from a "curse in any field".
      • neepi 1y ago
        That would assume that the entire world hasn't already tried this a thousand times over. Measurements are standardised communication tools. If you start changing the definitions, things fall out of the sky and on your head.
        • baxuz 1y ago
          This mindset is why the US is still using barley seeds as a standardized unit of measure.
        • 1y ago
• jeremyscanvic 1y ago
  Another surprising place decibels pop up, pretty far from loudness related things, is in image comparison metrics. Peak signal-to-noise ratio is mean squared error normalized by a certain peak intensity and it is generally expressed in dB, i.e. as 10 log10(normalized mse). https://en.m.wikipedia.org/wiki/Peak_signal-to-noise_ratio https://en.m.wikipedia.org/wiki/Peak_signal-to-noise_ratio Edit: typo
  • rocqua 1y ago
    Decibels make a lot of sense for ratios in any kind of signal processing. They are not that suited to sound, but sound is generally hard to quantify.
• fouronnes3 1y ago
  When I worked on a radar project, my fellow radar engineers (I'm software) used dB a lot. A lot of them would actually agree with the article, but historical sometimes wins even when you're aware of its shortcomings. Aren't we the same in software anyway? The email protocol, terminal escape sequences, the UX of git command line, etc... Each of those could have an "X is ridiculous" blog post (and I would enjoy every single one). One upside of dB not touched in the article is that it changes multiplication into addition. So you can do math of gains and attenuations in your head a bit more conveniently. Why this would be useful in the age of computers is confusing, but on some radio projects both gains and losses are actually enormous exponents when expressed linearly, so I sort of see why you would switch to logs (aka decibels). Kinda like how you switch to adding logs instead of multiplying a lot of small floats for numerical computing.
  • lxgr 1y ago
    > A lot of them would actually agree with the article, but historical sometimes wins Indeed – as evidenced by some parts of the world still using non-metric units in daily life or even engineering :)
    • perching_aix 1y ago
      As a European if somebody tells me the diagonal size of a display in cm or meter, I'm simply not able to "grasp" it. I need to whip out the calculator and divide by 2.54, turning it into inches. It's just how monitors are measured in my head at this point.
      • lxgr 1y ago
        When the Euro was introduced, I've heard people say things like "older generations will never adapt to the new currency, they'll always refer to the old denominations in their head" – which turned out to be completely untrue. Adapting to new units is very possible, but it needs a concerted effort. Absent a good inherent reason or anybody capable of artificially creating one, it won't happen on its own.
• lifthrasiir 1y ago
  The only thing you should know is that any use of bel and thus decibel should ideally have the reference level suffixed (usually in parentheses or subscript), not implied. The absolute sound pressure level is dB(SPL). The human-perceived loudness level is dB(A) and similar. The RMS voltage expressed in power is dB(u) (formerly dB(v), not same as capital dB(V)). And so on. And then each different instance of dB unit is simply distinct, only connected by the fact that it represents some ratio in the logarithmic fashion. Treat any new dB unit you haven't seen as an alien.
  • hashhar 1y ago
    This is exactly it. The people who get confused by decibels are treating it a unit in it's own right when it's really just a ratio of some unit.
    • margalabargala 1y ago
      Disagree. The people who get confused by decibels, are exposed to other people treating it like it's a unit in its own right. I agree that what the parent described, should be done. If it was what was done, this article wouldn't exist.
      • lifthrasiir 1y ago
        As I've said in the other comment, I believe this should be ultimately addressed by the SI.
        • margalabargala 1y ago
          I would agree. Right now what we've got is basically "millis", and you just have to know whether the speaker is talking about length or mass. I like your proposal.
          • lifthrasiir 1y ago
            I actually want those suffixes mandatory, because there may be multiple plausible suffixes for each use. For example the loudness might be dB(A), dB(B), dB(C), dB(D) depending on the exact curve or even dB(SPL) if the sound pressure level is used as a proxy. So it is much more confusable than, say, "millis" when suffixes are implied.
• yuvadam 1y ago
  Decibels aren't actually that ridiculous if you just accept them as plain logarithmic ratios, between your signal and the noise floor or some other signal. (Or between anything else, really.) 3dB is roughly double, 10dB is 10x, but only sounds about twice as loud because our ears are weird.
• kazinator 1y ago
  > This means that if you’re talking about watts, +1 bel is an increase of 10×; but if you’re talking about volts, it’s an increase of √10×. This is nuts: it’s akin to saying that the milli- prefix should have different meanings depending on whether we’re talking about meters or liters. Well no, because even if you are focusing on a signal measured in volts, the bel continues to be related to power and not voltage. As soon as you mention bels or decibels, you're talking about the power aspect of the signal. If volume were measured in meters, which were understood to be the length of one edge of a cube whose volume is being given, then one millimeter (1/1000th of distance) would have to be interpreted as one billionth (1/1,000,000,000) of the volume. When you use voltage to convey the amplitude of a signal, it's like giving an area in meters, where it is understood that 100x more meters is 10,000x the area. There could exist a logarithmic scale in which +3 units represents a doubling of voltage. We just wouldn't be able to call those units decibels.
  • dj3l4l 1y ago
    The Bel is a unitless quantity. Yes, by convention, in certain fields, it applies to the logarithm of the ratio of powers. But in other fields (for example, quantifying a change in the degree of evidence for a hypothesis, as in Bayesian probability theory) it is applied to a ratio of different quantities (in the Bayesian case, a ratio of probabilities). There is no reason why dB can't be used for any unit, and its meaning is incomplete until the denominator of the ratio within the logarithm is known. This is the gripe that is being conveyed in this article. Mathematically, the Bel is unitless. It is only by additional context that one can understand the value of the denominator in the logarithm.
    • paipa 1y ago
      The denominator isn't the issue. The context-dependent base of the logarithm is, which makes 1 Bel = 10x for some things and 1 Bel = 3.16x for others. I've never heard of decibels used in probability theory. Did they adopt it with the same baked-in bastardizations? Please tell me +10dB(stdev) = +10dB(variance) isn't a thing.
      • 1y ago
• leoedin 1y ago
  I worked in RF (radar) for a while and the dB/dBm is an incredibly useful tool there. It makes reasoning about amplifier chains and insertion loss so much more straightforward. It also means you can talk about transmitters and receivers in a comparable unit - in reality the signals are many many orders of magnitude apart.
• kazinator 1y ago
  The confusing thing about decibels is not the Watts versus Volts thing. It is the following. If you mix two identical signals (same shape and amplitude) which are in phase, you double the voltage, and so quadruple the power, which is +6 dB. But if you mix two unrelated signals which are about the same in amplitude, their power levels merely add, doubling the power: +3 dB.
  • cycomanic 1y ago
    That has nothing to do with decibels at all, that's the fundamental physics (or mathematics if you want) of adding waves, i.e. interference.
    • kazinator 1y ago
      Sure, but people who are confused by the voltage vs power thing (also fundamental physics) will likely be quadruply confused by this.
  • mousethatroared 1y ago
    If they're identical and in phase, the addition is obviously a multiplication by 2 -> 6dB. If they're unrelated the signals can also cancel out. So not 6bB. If not 6 dB then what is it? An integral that has already been solved for us :D
• calmbonsai 1y ago
  If you're specifying decibels in written form you always include the basis or you're simply being incomplete with your units. I don't understand the complaint there. In casual conversation, the context implies the basis. Dealing with decibels is also another shorthand to know the domain has a wide enough value gamut such that logarithmic values (where addition is multiplication) makes sense. See also, the Richter scale.
  • Aachen 1y ago
    > If you're specifying decibels in written form you always include the basis or you're simply being incomplete with your units. I don't understand the complaint there. It seems that a lot of people who are specifying decibels in written form aren't aware of what you just said Did you ever see someone use p as a unit and expect anyone to understand it means pico? Because I've seen that with dB. In this very thread. You really don't have to look far for the tendency for dB to be used as incomplete unit > See also, the Richter scale Looking at the article and trying to substitute Richter, I can't imagine what you'd plug in the different positions: - it's not a derivative of another relative unit (no decirichter) - it was not originally meant for something else (dB was originally meant for power, leading to difference in meaning of dB in dB(V) vs. dB(W), if I'm understanding the article correctly) - it's not trying to indicate the magnitude of the actual unit (you don't specify Richter-Volts or something, just Richter, so you can't forget to specify the actual unit) - there aren't different meanings depending on the field you're in (a –45dB microphone is mentioned in the article as referring to Volts whereas an acoustic 10dB loudness difference is apparently in Pascals; Richters are always Richters) The article criticises a lot of dB's aspects but I'm not sure the exponentialness is one of them
  • viraptor 1y ago
    > I don't understand the complaint there. The problem is that almost nobody does. I can't remember the last time outside of HN comments here that I've seen dB(A) or similar in real world.
    • calmbonsai 1y ago
      I guess I'm biased from my Electrical Engineering background as we use different decibels all the time so the basis is essential. It would be akin to saying 'kilo', but not specifying a 'gram', or 'meter'. That's fine for bakers as they don't work with kilometers routinely, but not for physicists or antenna engineering.
• badlibrarian 1y ago
  Horsepower is a unit of measurement. There's hp and bhp and hpE and... "Other names for the metric horsepower are the Italian cavallo vapore (cv), Dutch paardenkracht (pk), the French cheval-vapeur (ch), the Spanish caballo de vapor and Portuguese cavalo-vapor (cv), the Russian лошадиная сила (л. с.), the Swedish hästkraft (hk), the Finnish hevosvoima (hv), the Estonian hobujõud (hj), the Norwegian and Danish hestekraft (hk), the Hungarian lóerő (LE), the Czech koňská síla and Slovak konská sila (k or ks), the Serbo-Croatian konjska snaga (KS), the Bulgarian конска сила, the Macedonian коњска сила (KC), the Polish koń mechaniczny (KM) (lit. 'mechanical horse'), Slovenian konjska moč (KM), the Ukrainian кінська сила (к. с.), the Romanian cal-putere (CP), and the German Pferdestärke (PS)." [1] Decibel is not a unit of measurement. Decibels are a relative measurement. It tells you how much louder or powerful something is relative to something else. And frankly far less ridiculous than horsepower, which has a hilarious Wiki article if you read it with a critical mindset. Deriving some of the constants without Googling is a fun exercise to verify that you're not as smart as you think you are. "Hydraulic horsepower = pressure (pounds per square inch) * flow rate (gallons per minute) / 1714" [1] https://en.wikipedia.org/wiki/Horsepower https://en.wikipedia.org/wiki/Horsepower
  • thaumasiotes 1y ago
    > "Other names for the metric horsepower are [...]" I'm not clear on what point you think you're making. Is it interesting that the same thing might have different names in different languages? That subsection of the article, by the way, is obviously lying: > The various units used to indicate this definition (PS, KM, cv, hk, pk, k, ks and ch) all translate to horse power in English. cv and ch translate to steam horse, which isn't hard to see even if you only speak English. What does "vapor" mean to you? The opening of the article does suggest some problems, though not problems that wouldn't apply to the word "ounce". But you seem to have pulled an extended quote describing a completely expected state of affairs, while ignoring this: > There are many different standards and types of horsepower. Two common definitions used today are the imperial horsepower as in "hp" or "bhp" which is about 745.7 watts, and the metric horsepower as in "cv" or "PS" which is approximately 735.5 watts. The electric horsepower "hpE" is exactly 746 watts, while the boiler horsepower is 9809.5 or 9811 watts, depending on the exact year. I don't get it.
• bob1029 1y ago
  I think dB is a good way to represent certain user interfaces. I've always preferred to operate my audio equipment using a logarithmic scale. Changing the volume is much more intuitive to me this way than with some linear 0-100 mapping.
• severusdd 1y ago
  While I thoroughly enjoyed reading this piece of internet-rant, I've to argue that dB is still probably the best we have on this! In RF engineering, expressing signal levels in dBm or gains in dB means you can add values instead of multiplying, which definitely appeared like a huge convenience for my college assignments! A filter with -3 dB loss and an amplifier with +20 dB gain? Just add. You can also use this short notation to represent a variety of things, such as power, gain, attenuation, SPL, etc. I guess, engineers don’t use dB because they’re masochists (though many of them surely are). They use it because in the messy world of signals, it works. And because nobody knows anything that might work better!
  • modeless 1y ago
    There's nothing wrong with using a logarithmic system, that's not the complaint here. The complaint is that using decibels instead of bels is weird, and also that it's a scale and not a unit but people use it as if it was a unit without specifying a reference point, and also that the scale changes for different base units. Crazy how many people here are missing the point.
    • blackguardx 1y ago
      dBm is fully defined. Its reference is 1 mW into 50 ohms. I agree that using dB as a unit and not as a comparison (10 dB more power) is confusing, though.
• em3rgent0rdr 1y ago
  > For some reason, the bel — again, what started as a sensible 10× increment — was soon deemed too big to use. I don’t quite know why: in other aspects of life, decimal notation suits us just fine. Decimal notation can be a tad cumbersome to write and speak. Meanwhile, decibel usage commonly results in nice simple numbers that range between 0 and 100, with the fractional digits often being too insignificant to say out loud. For instance, the dynamic range of 16-bit audio (which is generally all the range that our ears care about) is 96 dB, while volume increments smaller than 1 dB aren't really noticeable, so decibel makes it easy to communicate volume levels without saying "point" or writing a "." or breaking out exponential notation. Even in fields other than audio the common ranges also conveniently will be around 1 dB for being on the verge of significance to around 100 dB or 200 dB for the upper range. (Also the whole power vs root-power caveat is simply something users of dB have to be cognizant of because we need to stick with one or the other to make consistent comparisons, and at the end of the day physical things hapen with power.) So while decibels may seem ridiculous, they actually are quite convenient for dealing with logarithmically-varying numbers in convient range from 1 dB to around 100 dB or so in many engineering fields.
  • em3rgent0rdr 1y ago
    Its like why we use percent from 0% to 100% instead of speaking of ratios from 0 point something to 1.
• cousin_it 1y ago
  Yeah. And don't get me started on the folks who think "6dB/octave" is a reasonable thing to say. Which is, apparently, everyone who works with audio filters except me.
  • jpc0 1y ago
    How else would you describe what occurs other than 6dB/octave?
    • badmintonbaseba 1y ago
      Notice how both dB and octave are ratios, but for some reason for frequency ratios we don't use bels or decibels. An octave is a ratio of 2, a bel is a ratio of 10.
      • nayuki 1y ago
        For frequency, a decade is a ratio of 10, akin to a bel. And in photography, a stop or an EV is a factor of 2, akin to an octave. https://en.wikipedia.org/wiki/Logarithmic_scale#Common_uses https://en.wikipedia.org/wiki/Logarithmic_scale#Common_uses
    • cousin_it 1y ago
      For a 6dB/octave lowpass filter, I would say power gain is inversely proportional to frequency squared (1/f^2). There's precedent for this notation, for example pink noise is known as both 3dB/octave and as 1/f.
• taneq 1y ago
  You use a unit that maps well between the thing you want to measure and the thing you want to know about it. If you do this enough with the same until you give it a name. I don’t get the author’s complaint.
  • mjaseem 1y ago
    When you want to measure a related but different quantity, don't use the same name as the first one because that leads to confusion. This rule is not followed by Decibel and that is complaint.
• undebuggable 1y ago
  If decibels in acoustics confuse you, try learning decibels in optical communication. That's a witchcraft.
• varjag 1y ago
  Decibels are not anywhere near as ridiculous as Marketing Kilobytes introduced in the 1990s. Pot, meet kettle.
  • nayuki 1y ago
    This is one of those cases where marketing is correct. Oh tell me, if your CPU processes 1 byte in 1 cycle, and it runs at 800 MHz, how many bytes does it process in 1 second? The answer is 800 million bytes, or 800 (real) megabytes. It cannot be 800 mebibytes. (Equal to 763 mebibytes.) Similarly, let's say we have a 1-bit Boolean attribute for each person in the world, and the world population is 8 062 000 000 billion people. How many bits do we need in our database? It's 8.062 gigabits, not 8.062 gibibits. (Equal to 7.508 gibibits.) The telecom industry has always used power-of-1000 prefixes on bits and bits per second. You have a gigabit Ethernet LAN, and assume no protocol overhead. How long does it take to transmit a 4.7 GB (real gigabytes) DVD image? Multiply by 8 to convert from bytes to bits, so that's 37.6 Gb, so that will take 37.6 seconds to transmit. But how long does it take to transmit a "700 MB" (actually MiB) CD image? Well, it's 734 MB (real megabytes), so 5872 Mb, which is 5.872 seconds. The problem with the abusively overloaded definition that 1 kilobyte = 1024 bytes, 1 megabyte = 1048576 bytes, etc. is that it fails to align with the rest of the metric system, or even how we group decimal numbers into thousands and millions. The computer industry is wrong here. And now you have the problem that you can't fit a memory dump of "16 GB" of RAM onto a "16 GB" flash memory card, because the former is actually GiB but the latter is real GB.
    • varjag 1y ago
      > Oh tell me, if your CPU processes 1 byte in 1 cycle, and it runs at 800 MHz, how many bytes does it process in 1 second? An interesting metric, used by noone in the Universe except you for the sake of this discussion. But let's entertain this: if the actual CPU speed is 838,860,800Hz, how many bytes does it process in 1 second? > Similarly, let's say we have a 1-bit Boolean attribute for each person in the world I have no problem with definition of bits. > And now you have the problem that you can't fit a memory dump of "16 GB" of RAM onto a "16 GB" flash memory card, because the former is actually GiB but the latter is real GB. Remarkable circular reasoning, since the Marketing Kilobyte was defined in the 1990s precisely to inflate actual storage sizes without getting class action suits. > it fails to align with the rest of the metric system Look, byte is not derived from fundamental units. It is thus not a part of metric system so SI has zero business regulating information storage. On the other hand you can't buy a computer that does not address memory in anything other than powers of two. Nor you could ever buy a 1000 million bytes RAM chip, because they don't ever exist for basic reason that binary computers use 2^n addressable space.
• nyanpasu64 1y ago
  I have a vague report that "root-power" or voltage-like quantities (20 dB per order of magnitude) are signed or vector-like, while power-like quantities are unsigned scalars?
• nabla9 1y ago
  Decibel is ridiculously overloaded concept. It can be used to express and calculate relative change in power, amplitude ratios, and absolute change. All of these are different units and should always use different notation, but sometimes it's skipped.
  • stephen_g 1y ago
    But a lot of them can be combined - like you can take dBm of a microwave signal going into a filter, subtract the dB figure of loss through a filter, add the dB figure of gain through an amplifier, then add the dBi of antenna gain, and get a meaningful number (equivalent isotopic radiated power or EIRP, in dBm) out the end! It’s quite amazing!
    • deleted 1y ago
      [deleted]
• amai 1y ago
  Fahrenheit on the other hand makes sense...
• pajko 1y ago
  Loudness is not measured in dB, but in phon (https://en.wikipedia.org/wiki/Phon https://en.wikipedia.org/wiki/Phon) or sone (https://en.wikipedia.org/wiki/Sone https://en.wikipedia.org/wiki/Sone).
  • mattclarkdotnet 1y ago
    Or dB(SPL) as a ratio of the phon.
  • dubcanada 1y ago
    Tell that to everyone on the planet who uses dB
• cesaref 1y ago
  Generally speaking, the db scale is very useful for many practical situations, and this is overlooked in this critique. As have been pointed out, it's just a power ratio on a logarithmic scale, but this has many benefits, the main one being that chaining gain/attenuation in a system is just a case of adding the db values together. 'We're loosing 4db in this cable, and the gain through this amp is 6db, so the output is 2db hotter than the input'. Talk to any sound engineer and you'll do this sort of thing successfully without necessarily understanding the science, so that's a massive win.
  • remram 1y ago
    I didn't get that reading the article. The author acknowledge that ratios are useful, but that there are specific problems in how we use this unit and how we picked and express the reference scales. > On the face of it, the idea makes sense. Your specific example is a pure ratio so there's no problem with it (there is no reference). Apart from the fact that I have to guess whether you are measuring volts or watts through your cables, of course...
    • BenjiWiebe 1y ago
      So what I learned today, via another comment and confirmed with a dictionary, is that decibels (unspecified reference) is NOT pure ratio - it's a _power_ ratio. So it will be Watts, not Volts.
      • bitdivision 1y ago
        But that's why it's so confusing. Did they purposefully leave off the reference to indicate Watts, or did they mean volts (as I'd guess audio engineers typically do when talking about amplifiers).
        • BenjiWiebe 1y ago
          No, it isn't Watts if there's no reference. It's a ratio of powers. i.e. amplification or attenuation. To have an actual amount of power, you need to reference it to some particular amount of power, like dBm for power-ratio-relative-to-milliwatt.
• layer8 1y ago
  Tangential question: Are there any sound meters that can actually measure down to 0 dB? The best I’ve seen specify 20 dB, which to me is still very audible. (Note that, as the article mentions, 0 dB doesn’t mean “zero sound pressure”, but just “threshold of hearing”.)
  • danadam 1y ago
    Some laboratory-grade equipment probably. > 0 dB doesn’t mean “zero sound pressure” From the decibel definition, zero of anything is -∞ in dB_suffix scale.
    • layer8 1y ago
      > Some laboratory-grade equipment probably. I wasn’t able to find any listings, that’s why I’m asking.
• 867-5309 1y ago
  still doesn't answer what 0.3 Sone is in dBA
• dogman1050 1y ago
  His first equation is wrong. It should be P=V^2/R, not P=V^2R.
• halayli 1y ago
  this is one of the best videos to understand what a dB is and when it is used, and how to interpret them. what's unique about this unit is it relies a lot on the context. https://www.youtube.com/watch?v=1mulRI-EZ80 https://www.youtube.com/watch?v=1mulRI-EZ80
• TacticalCoder 1y ago
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• numpad0 1y ago
  I just can't understand why "[specialized domain] uses these stupid wrong units, it should be [unit that no educated smart SMEs use]" types don't do their researches to understand why those are used at all. This type of weird non-SI units appear when means of measurement and unit is related to one another and has downstream dependencies. Just look at aviation. An airplane's: - speed is measured in knots, or minute of angle of latitude per hour, which is measured by ratio of static and dynamic pressure as a proxy. - vertical speed or rate of climb is measured in feet per minute, which is a leaky pressure gauge, probably all designed in inches. - altitude is measured in feet, through pressure, which scale is corrected by local barometric pressures advertised on radio, with the fallback default of 29.92 inHg. When they say "1000ft" vertical separation, it's more like 1 inHg or 30 hPa of separation. - engine power is often measured in "N1 RPM %" in jet engines, which obviously has nothing to do with anything. It's an rev/minutes figure of a windmilling shaft in an engine. Sometimes it's EPR or Engine Pressure Ratio or pressure ratio between intake and exhaust. They could install a force sensor on the engine mount but they don't. - tire pressure is psi or pound per square inch, screw tightening torques MAY be N-m, ft-lbs, or in-lbs, even within a same machine. Sure, you can design a battery charging circuits in Joules, fly an airplane with a GPS speedometer, analog audio-radio circuitry in millivolts. Absolutely no one does. I think that cognitive dissonance should trigger curiosity circuitry, not rant mode. I mean, just type in "use of decibels[dB] considered harmful" at the box at chatgpt.com. It'll generate basically this article with an armchair version of the top comment here as the conclusion.
  • anilakar 1y ago
    Wait until you hear about unit conversions in aeronautical mental math. 1 NM across ground corresponds to 1000 or 100 feet of altitude in many conversion formulas. For small angles, sines and tangents are approximated by degrees of azimuth × distance in NM = 60.
• tim333 1y ago
  The author gives the downsides but not the upside of why it is like that. It's basically so it describes sound levels on an understandable scale with 0db being just audible and 100dB being very loud. It also corresponds to the energy carried by the sound - 0 dB is 1 pW per square meter so it is kind of a scientific unit. It's probably easier to have a measure that is understandable by the public and let engineers do conversion calculations for signal levels in networks than the other way around.
  • jeroenhd 1y ago
    I assume you mean dB(A) here, because the sound level at dB(SPL) depends on the reference pressure chosen (20 mPa for db(A) with a calibrated microphone) and the constants for dB(A) are applicable to a large part of human sound perception. Though, if you use human perception as a reference, you'll also need to take dB(B) and dB(C) into account, depending on the sound you're playing and where you're playing that sound. You can't use "dB" standalone. You need to specify what kind of dB you're talking about, because every field has different dBs that measure different units or are adjusted to different constants. 10dB is like 10k. 10dB is a tiny number if you're talking about volume, but blows your audio equipment if we're talking dB(u) or dB(v) (not to be confused with dB(V). In the same sense, 10k is a low number if it's the price for a new electric car, or an election changing amount of voters when talking about a population.
    • tim333 1y ago
      Ah - it's complicated I guess. I was looking at this stuff https://en.wikipedia.org/wiki/Sound_intensity#Sound_intensity_level https://en.wikipedia.org/wiki/Sound_intensity#Sound_intensit...
• cb321 1y ago
  Abbreviation confusability is relative to { in fact one might say measured by ;-) - number? entropy? etc. } the listener/reader's knowledge/exposure, much as sound levels need a reference distance. I have heard "bare K" refer to a great many different things, not just kilobits (transmission) or kilobytes (storage) or kilograms (drug trade) or kilometers (foot races) and on & on, but pages or items or etc. The fundamental problem is that some humans like to abbreviate while others get caught and annoyed by the necessary ambiguity of such abbreviation. Sometimes this can be the very same human in different contexts. ;-) In fact, there even seems to be some effect where "in the know people" do this intentionally - like kids with their slang - as a token of in-group membership. And yes, this membership is at direct odds with broader communication, by definition/construction. To me this article seems to be just complaining about "how people are". So it goes! This is the primary complaint. The secondary one about voltage and power and the ambiguity of the prefix itself was addressed in another comment (https://news.ycombinator.com/item?id=44059611 https://news.ycombinator.com/item?id=44059611).
  • nayuki 1y ago
    > I have heard "bare K" refer to a great many different things The worst of the worst is when it refers to kilometres. Like, "I'm selling my car on the used market and its odometer is 150k", where they mean "150k km", but stacked prefixes are not allowed in metric, so the correct notation is "150 Mm" or "150 megametres". I get immense pushback whenever I point this out - the response is usually along the lines of "but you know what I meant", and it inherently assumes that km is the universal unit for talking about distance traveled by car. I point out that this is as ridiculous as saying "the hard drive is 4k GB" because they grew up with gigabytes; no, the correct notation is either "4000 GB" or "4 TB". Also regarding bare k or kilo (especially キロ in Japanese), you can say something ridiculously ambiguous like "My scooter goes up to 30k for 90k and weighs 20k" (respectively km/h, km, and kg).
    • bombela 1y ago
      In 3D printing, I often catch people talking acceleration in kilo-milli-meter/second². Written and pronounced "16k accel". Instead of writing "16m/s²" and pronouncing "16 accel". I have nightmares of 150km meaning kilo-miles instead of kilo-metre. And when I say that my car has 260 mega-meter on the odometer, even people born metric look at me funny. And don't get me started on MB vs MiB. I have seen so many stupid production outages because of people miss-allocating resources by confusing SI and IEC bytes. /rant
• lambdaone 1y ago
  It's a bit like hating numbers, and saying "What do you mean by 'three'; what is it - three volts, three amps, three metres? Clearly 'three' is meaningless, and we should stop using it and all the other numbers besides." decibels are simply a dimensionless ratio, used as a multiplier for some known value of some known quantity. In every context where decibels are used, either the unit they qualify is explicitly specified, or the unit is implicity known from the context. For instance, in the case of loudness of noise to human ears in air, the unit can be taken to be dBA (in all but rare cases which will be specified) measured with an appropriate A-weighted sensor, relative to the standard reference power level. And similar (but different) principles apply to every other thing measured in dB; either theres an implicit convention, or the 0 dB point and measurement basis are specified. People who assume that everyone is an idiot but themselves are rarely correct. I look forward to the author discovering about (for example) the measurement of light, or colorimetry, and the many and various subtleties involved. The apparent excessive complexity is necessary, not invented to create confusion.
  • deleted 1y ago
    [deleted]
  • weinzierl 1y ago
    "decibels are simply a dimensionless ratio, used as a multiplier for some known value of some known quantity." Except they are not. 1 dB can sometimes mean a ratio of ~ 1.26 and other times it can mean a ratio of ~ 1.12. "In every context where decibels are used, either the unit they qualify is explicitly specified, or the unit is implicity known from the context." Maybe in university, but certainly not in the real world.
    • 20k 1y ago
      I have a feeling that a lot of people here haven't read the article. There's lots of "Its just a dimensionless ratio" comments
    • hgomersall 1y ago
      It's a power ratio. 1dB always means a power ratio of 1.26. That might mean a voltage or current ratio, say, of 1.12, but that is because the relationship between voltage ratios and power ratios is a simple square.
• ttoinou 1y ago
  Love this kind of articles but I wished the author suggested solutions. I go even further than this author : sometimes decibels are computed using logarithms and what we put inside the logarithm has a physical unit. But I can prove mathematically that this is wrong and that whats given to a log function has to be dimensionless. Hence a lot of dB calculus is mathematically wrong and physically meaningless
• adrian_b 1y ago
  Decibels are not ridiculous, but very frequently the notations for quantities expressed in decibels are ridiculous. The decibel is an arbitrary unit for the quantity named "logarithmic ratio". Logarithmic ratio, plane angle and solid angle are 3 quantities for which arbitrary units must be chosen by a mathematical convention and these 3 units are base units, i.e. units that cannot be derived from other units. For a complete system of base units for the physical quantities, there are other 3 base units for dynamic quantities that must be chosen arbitrarily by choosing some physical object characterized by those quantities, i.e. a physical standard (originally the 3 dynamic quantities were length, time and mass, but in the present SI the reality is that mass has been replaced by electric voltage, despite the fact that the text of the SI specification hides this fact, for the purpose of backward compatibility), and there also are other 2 base units for discrete quantities (amount of substance and electric charge) which must be established by convention. Like for the plane angle one may choose various arbitrary units, e.g. right angles, cycles, degrees, centesimal degrees, radians, or any other plane angles, for the logarithmic ratio one may choose various arbitrary units, e.g. octave, neper, bel, decibel. So if we choose decibel all is OK. Decibels have the advantage that for those used to them it is very easy to convert in mind between a logarithmic ratio expressed in decibels and the corresponding linear ratio, so it is very easy to make very approximate computations in mind, but good enough for many engineering debugging tasks, in order to replace multiplications, divisions and exponentiations with additions, subtractions and rare simple multiplications, for a quick estimate of what should be seen in a measurement in a lab or in the field. The problem is that whenever a logarithmic ratio is specified in decibels, it must be accompanied by 2 quantities, what kind of physical quantities have been divided and which is the reference value. Humans are lazy, so they usually do not bother to write these things, assuming that the reader will guess them from the context, but frequently the context is lost and guessing becomes difficult or impossible. An additional complication is that one never uses logarithmic ratios for electric voltages or currents, but only for powers. When it is said that a logarithmic ratio refers to a voltage or a current, what is meant is that the logarithmic ratio refers to the power that would be generated by that voltage or current into an 1 ohm resistor. A similar problem exists for sound pressures, because logarithmic ratios are used only for sound intensities, so where sound pressure is mentioned, actually the corresponding sound intensity is meant. This complication has appeared because voltages, currents and sound pressures are what are actually measured, but powers and sound intensities are frequently needed and using logarithmic ratios with different values for related quantities, while omitting frequently to mention the reference value, would have caused even more confusion than the current practice.
• FRidh 1y ago
  The problem with using decibels is that since it is a relative unit you need to know what it is relative to, and that is often not just the unit but also the quantity. Unfortunately, this part is (as expressed) at times omitted or put in the wrong place. And its often also the engineers in the respective fields that keep using this incorrect notation spreading the confusion for those outside the domain. E.g., acoustic engineers often write db(A) for A-weighted sound pressure levels. Yes, it is often noted this way, but it is incorrect. The correct way is to specify the quantity and that the quantity is A-weighted, `L_{p, A} = 80 dB` for example to express an A-weighted sound pressure level of 80 dB. Regarding sound pressure and sound power. Sound power is not expressed using A-weighting because it does not make sense. Sound power is a property of the source. A-weighting is a property of the receiver, that is, the human listener.
  • rightbyte 1y ago
    > The problem with using decibels is that since it is a relative unit you need to know what it is relative to Ye but that is also the point. The author seem to prefer to memorize dozens of absolute values.
• thinkingtoilet 1y ago
  Not surprisingly, Tom Scott has an interesting video on this: https://www.youtube.com/watch?v=Is_wu0VRIqQ https://www.youtube.com/watch?v=Is_wu0VRIqQ
• lamename 1y ago
  I appreciate the sentiment, but I've found this resource [0] much more direct and comprehensive. It explains all of the nuance regarding dB and related terminology from audio engineering to perception (voltage, power, intensity, volume, loudness, etc.) The format is a bit circular; just enjoy getting lost in it for half an hour. https://sengpielaudio.com/TableOfSoundPressureLevels.htm https://sengpielaudio.com/TableOfSoundPressureLevels.htm
• HPsquared 1y ago
  It's a bit like "percent". A shorthand for dealing with ratios, often with hidden assumptions.
  • colejohnson66 1y ago
    Sure, but you never say "the production is at 50%". 50% of what? Peak possible output? Typical output? That's what the author's complaint is: dB, while arguably useful, is annoying because people leave out the part that it's relative to. And then people, when talking about dB, assume the other party has knowledge of what their ratio is relative to. dBm, dbSPL, etc.
    • davrosthedalek 1y ago
      In every communication, the sender assumes that the other party has some knowledge. For example, I assume that you can read my badly worded English text. There is rarely confusion with the people in the fields that use dB a lot. That other people often get confused by dB is not a failure of dB, not even of its common use, the same way I can't blame English for not being Chinese, or for Americans use F instead of C, or K, for temperatures.
  • BlueTemplar 1y ago
    Insert mandatory complaint about percentages being misused : their point is the approximation : 1.02×1.03~1.05 <=> +2%+3%~+5%, which only holds up to low tens +/-%.
    • nayuki 1y ago
      There is a solution for you - log points! https://en.wikipedia.org/wiki/Relative_change#Logarithmic_change https://en.wikipedia.org/wiki/Relative_change#Logarithmic_ch... , http://a-loonie-saved.blogspot.com/2008/08/log-points.html http://a-loonie-saved.blogspot.com/2008/08/log-points.html An example of deceptive arithmetic: A mutual fund's 5-year history of annual returns is −70%, +30%, +50%, +20%, +40%. Naively, the total return for the 5-year period looks like +70%. But in fact it's −1.72%, because the reciprocal function makes the −70% very “heavyweight” compared to the positive changes. Using log points instead, the 5-year sequence is approximately −120.4, +26.2, +40.5, +18.2, +33.6. The sum of these rounded numbers is −1.9 (nowhere near +60.0), which agrees well with the correct result of about −1.735 log points (i.e. −1.72%).
• kragen 1y ago
  This is an incredibly valuable article for anyone who's trying to make sense of decibels in some context. Michał clearly explains almost all of the gotchas you have to understand. I realized recently, after years of doing it for signal powers, that dB are a pretty convenient way to do mental logarithmic estimates for things that have nothing to do with power or signals, with only a small amount of memorization. Logarithms are great because they allow you to do multiplication with just addition, and mental addition isn't that hard. For example, if you want to know how many pixels are in a 3840×2160 4K display, well, log₁₀(3840) ≈ 3.58 (35.8dB-pixel) and log₁₀(2160) ≈ 3.33 (33.3dB-pixel), and 3.58 + 3.33 = 6.91 (69.1 dB-square-pixel), and 10⁶·⁹¹ ≈ 8.13 million. The correct number is 8.29 million, so the result is off by about 2%, which is precise enough for many purposes. (To be fair, though, 4000 × 2000 = 8000, which is only off by 3.5%.) The great difficulty with logarithms is that you need a table of logarithms to use them, and a mental table of logarithms is a lot of rote memorization. You can get pretty decent results linearly interpolating between entries in a table of logarithms, so you can use a lot more logarithms than you know, but you have to know some. It's pretty commonplace in EE work to make casual use of the fact that a factor of 2× [in power] is about 3 dB, which is a surprisingly good approximation (3.0103dB is a more precise number). This is related to the hacker commonplace that 2¹⁰ = 1024 ≈ 1000 = 10³; 1024× is 30.103dB, while 1000× is precisely 30dB. To the extent that you're willing to accept this approximation, it allows you to easily derive several other numbers. 4× is 6dB, 8× is 9dB, 16× is 12dB, and therefore 1.6× is 2dB. ½× is -3dB, so 5× is 7dB (10-3). So with just 2× = 3.01dB we already know the base-10 logarithms of 1, 2, 4, 5, and 8, to fairly good precision. That's half of the most basic logarithm table. (The most imprecise of these is 8: 10⁰·⁹ is about 7.94, which is an error of about -0.7% when the right answer was 8.) If we're willing to add a second magic number to our memorization, 3× ≈ 4.77dB. This allows us to derive 6× ≈ 7.78dB and 9× ≈ 9.54dB. So, with two magic numbers, we have fairly precise logarithms for 1, 2, 3, 4, 5, 6, 8, and 9. The only multiplier digit we're missing is 7. (Shades of the Pentium's ×3 circuit: http://www.righto.com/2025/03/pentium-multiplier-adder-reverse-engineered.html http://www.righto.com/2025/03/pentium-multiplier-adder-rever....) So a third magic number to memorize is that 7× ≈ 8.45dB. And now we can mentally approximate products and quotients with mentally interpolated logarithms. You can do my example above of 3840×2160 as follows. 3.8 is 80% of the way from 3 (4.8dB) to 4 (6.0dB), so it's about 5.8dB. 2.2 is 20% of the way from 2 (3.0dB) to 3 (4.8dB), so about 3.4dB. 35.8dB + 33.4dB = 69.2dB, which is between 8 million (69.0dB) and 9 million (69.5dB), about 40% of the way, so our linear interpolation gives us 8.4 million. This result is high by 1.2%, which is much better than you'd expect from the crudity of the estimation process. For a more difficult problem, what's the diameter of a round cable with 1.5 square centimeters of cross-sectional area? That's 150mm², half of 300mm², so 24.77 dB-square-millimeters minus 3.01, 21.76dB. A = πr². Divide by π by subtracting 5dB (okay, I guess that's a fourth magic number: log₁₀(π) ≈ 4.97dB) and you're at 16.76dB. Take the square root to get the radius by dividing that by 2: 8.38dB-millimeters. That's less than 7× ≈ 8.45dB by only 0.07dB, so 7-millimeter radius is a pretty decent approximation, 14mm diameter. The precise answer is closer to 13.82mm. For approximating small corrections like that, it can be useful to keep in mind that ln(10) ≈ 2.303 (a fifth magic number to memorize), so every 1% of a dB (10¹·⁰⁰¹) is a change of about 0.23%. So that leftover 0.07dB meant that 7mm was high by a couple percent. More crudely: 150mm² is 22dB, ÷π is 17dB, √ is 8½ (pace Fellini), 7×. It's pretty common in engineering and scientific calculations like this to have a lot of factors to multiply and divide, increasing the number of additions and subtractions relative to the number of logarithmic conversions; this is why slide rules were so popular. Maybe you derived the 1.5cm² number from copper's conductivity and a resistance bound, or from the yield strength of a steel and a load, say. 3840×2160 pixels × 4 bytes/pixel / (10.8 gigabytes/second), as I was calculating last night in https://news.ycombinator.com/item?id=44056923 https://news.ycombinator.com/item?id=44056923? That's just 35.8 dB + 33.3dB + 6dB - 100.3dB = -25.2dB-seconds, which is 3.0 milliseconds to memcpy that 4K framebuffer. (I didn't do that mentally, though.) Even 36 + 33 + 6 - 100 = -25, so π ms, is a fine approximation if what you want to know is mostly whether it's more or less than 16.7 ms. So here's a full list of the seven magic numbers to memorize for these purposes: 2× ≈ 3.01dB (∴ 4×, 8×, 5×) 3× ≈ 4.77dB (∴ 6×, 9×, 1.5×) 7× ≈ 8.45dB π× ≈ 4.97dB ln(10) ≈ 2.303 (∴ 0.01dB ≈ 0.23%, etc.) 1.259× ≈ 1dB (+1dB ≈ +25.9%) (1 - .206)× ≈ -1dB (-1dB ≈ -20.6%) I haven't been applying this approach long; I'll try to report on results later.
• elfrinjo 1y ago
  I'll summarize: It's annoying that dB is often used as a physical unit without the necessary suffix. It's annoying that the suffix seems quite random for most units It's annoying that the factor for power differs from the factor for voltage, etc. It's slightly annoying that it's usually decibel instead of Bel. However, we all agree that dBs are really useful.
  • Aachen 1y ago
    > However, we all agree that dBs are really useful. Which part of the article was that again? I was surprised to see that conclusion as summary because it's not what the takeaway seemed like to me, so went back to the article and I don't see this mentioned, perhaps I'm overlooking it because I didn't do a careful read a second time
    • elfrinjo 1y ago
      oh sorry; thats the comments
• deleted 1y ago
  [deleted]
• DonHopkins 1y ago
  Almost as annoying as Euler angles, which force you to choose an arbitrary ordering (XYZ, ZYX, ZXZ, …), while each choice is equally valid yet mutually incompatible, so there is no canonical “true” yaw-pitch-roll. Not to mention gimbal-lock singularities, wrapping discontinuously at +/-PI, mapping one orientation to many triples, and forcing you to juggle trig identities just to compose two spins. To pure mathematicians obsessed with elegant unambiguous coordinate-free clarity, Euler’s pick-any-order gimmick is like hammering tacky street signs onto the cosmos: a slapdash, brittle hack that smothers the true geometry while quaternions and rotation matrices sail by in elegant, unambiguous splendor.
• 49pctber 1y ago
  The idea that helped make decibels click for me is that they're a way to quickly do both dimensional analysis and gain/attenuation calculations at the same time. "Plain" decibels are simply (power) ratios. These can describe multiplicative changes in power. These are positive for gains (like in a power amplifier) or negative for attenuations (like path loss). They are unitless quantities. Decibels add. A ten 10 dB gain (x10) followed by a 20 dB loss (x0.01) is -10 dB (x0.1). "Flavored" decibels are in reference to some power quantity. For example, dBm uses one milliwatt as its reference. So 2 mW / 1 mW = 2 = 10^(3/10) = 3 dBm. These quantities have associated units, but they're still technically dimensionless. Here's the key insight. You can only have one "flavored" decibel value per computation. Say you have some 3 dBm signal (2 mW). You can add as many regular decibel values as you want, but the unit is still dBm. 3dBm + 4 dB - 7 dB = 0 dBm. In linear units, 2 mW * 2.5 * 0.2 = 1 mW If you were to do something like 3 dBm + 0 dBm, the linear units would be 2 mW * 1 mW = 2 mW^2, which is probably not what you want. dBs are confusing. Different fields have slightly different conventions. People talk about any factor of 2 as a 3 dB change, when technically it should only be relative to power-like quantities. It's weird that some of these "units" can be added together, while others can't. The factors of 10 and 20 can be confusing. But if you consider the units from a dimensional analysis standpoint, decibels are much more sane and intuitive than they appear.
  • timerol 1y ago
    > 2 mW / 1 mW = 2 = 10^(3/10) = 3 dBm It's worth noting that this is wrong, in exactly the way that makes decibels confusing. 3 dBm is an absolute power figure (about 2 mW). 2 mW / 1 mW is a ratio of 2 (about 3 dB). 2 mW / 1 mW = 2 = 10^(3/10) = 3 dB. 2 mW = 2 * 1 mW = 10^(3/10) * 1 mW = 3 dB (1 mW) = 3 dBm.
    • 49pctber 1y ago
      Yeah, that's a better way of thinking about it. That way you don't have any phantom bookkeeping like the way I was taught. The units are still right there.
    • QuarterReptile 1y ago
      Similarly, but in a very different context: I have to teach non-engineers C programming for an undergrad course, which is basically trying to teach very explicit attention to punctuation (among many other things). "Watch those double quotes!", "single quotes, not double!", "where's your semi-colon??", and so on. Then, three weeks into the course, we're passing values by reference with &, and I get the question, "isn't that scanf missing the and-sign in front of the string name?", and I'm forced to answer, "that punctuation doesn't matter, this time," because the C standard makes & do nothing in front of a string specifically because so many people were confused about that fact that a string's variable name is already passing by reference.
• etskinner 1y ago
  Here's another related one that always bothers me: When you say something's loudness in decibels, you also need to specify a measurement distance. The author of this article even accidentally makes this omission: > It’s 94 dB, roughly the loudness of a gas-powered lawnmower And that distance is very important; the actual sound pressure measured is proportional to distance^2. So for a lawnmower measuring 94dB, let's say we assume that we're measuring at 1m. At 2m away, the sound is actually 91dB. And don't get me started about the fact that a halving in power is 3dB, that's just wacky. I wish we used base 2.
  • duped 1y ago
    > And that distance is very important; the actual sound pressure measured is proportional to distance^2. While we're sniping nerds, the inverse square law only applies in the far field (which is tautologically "far enough away for the source to behave as a point source and follow the inverse square law"). That's probably a good bit further than 1m for a lawnmower in the physical world. For loudpseakers you have to be about 2m away before the inverse square law kicks in, unless they've been designed to operate as line sources which decay linearly for a very long distance. For loud sound sources near barriers like the ground they behave like half point sources, which will eventually act like point sources but there's a good bit of distance before it is really measurable.
    • filterfish 1y ago
      Whether something is near field or far field is frequency dependent
• RicoElectrico 1y ago
  This difference in mindset makes me comfortable as an EE that all the laid-off SWEs aren't going to take my job. Granted, demand side of the job market isn't rosy due to macro conditions, but at least supply isn't.
• stdbrouw 1y ago
  One way to illustrate some of the weirdness of dB is to look at the documentation of unit libraries, e.g.: https://pint.readthedocs.io/en/stable/user/log_units.html https://pint.readthedocs.io/en/stable/user/log_units.html https://painterqubits.github.io/Unitful.jl/v0.7/logarithm/ https://painterqubits.github.io/Unitful.jl/v0.7/logarithm/
• karmakaze 1y ago
  The writing style is antagonistic like a clickbait title. I find it bothersome. I would have much preferred an organized breakdown of all the different ways dB are used and what they mean instead of a random rant. It complains about how unscientific 'the' unit is, knowing that it's not a single unit then adds little to sort it out.
• timerol 1y ago
  The one thing that really resonates with me from this article is also the silliest thing: Why decibels instead of bels? Everyone has multiplied in scientific notation before, and making a power ratio of 10^4 = 4 B would be so much more intuitive for conversion to absolute figures. It's a completely silly complaint, given that it's literally just a decimal point instead of a d, but it would make mental math of absolute conversions that much faster, especially for people who don't live and breathe amplifier chains all day. I want to live in a world where a radio can be specified as a -10.2 Bm sensitivity. -9 is three SI prefixes down from 1 mW, so less than 0.1 pW.
• aimor 1y ago
  Yes, dB is a mess and if we could do it again we ought to use something more explicit like just annotating the units with log10 such as log10(W). Then it's easy to use other convenient units like log2(W) or if you want to reproduce dBV: 20log10(V). dB is fine shorthand, but it gets used all the time in places where things should be explicit.
• stevage 1y ago
  Gosh, I didn't know it was that bad - I didn't know it was used for so many different things.
• amelius 1y ago
  Speaking of which. Does anyone know why, in Physics, we only use the operators +, * and exponentiation? And why higher operators in the hyperoperation sequence are never used? https://en.wikipedia.org/wiki/Hyperoperation https://en.wikipedia.org/wiki/Hyperoperation
  • mik1998 1y ago
    You would use it if it was useful or convenient
    • amelius 1y ago
      It was more of a question about the nature of our universe, similar to: why are there only n spatial dimensions?
• gregschlom 1y ago
  "The bel is named in the honor of Alexander Bell; this is in the same tradition that prompted us to name the “wat” in honor of James Watt." This line killed me. I literally laughed out loud.
• teknopaul 1y ago
  "This is nuts: it’s akin to saying that the milli- prefix should have different meanings depending on whether we’re talking about meters or liters." Were were here recently with "mega": Sometimes mega is squared as in megapixels. Sometime not as in megabytes. No biggie. Db in audio is a relative scale and that makes perfect sense. If you mixer goes + or - 6db that makes sense but can't be measured as power, your mixer might not be plugged in to any speakers so relation to real power is moot in the digital realm. 3 eq bands with -+6db makes sense too. Doesn't need to be precisly specified to be of immediate value, +-12db is clearly something else and users know what.
  • perching_aix 1y ago
    > Sometimes mega is squared as in megapixels. Is that right? A pixel is a 2D object already. It's not like e.g. with centimeters, where it's a 1D unit, so it becomes centimeters squared to form a 2D unit.
    • deleted 1y ago
      [deleted]
    • davrosthedalek 1y ago
      it's (cm)^2, not c(m^2). If there would be the one-dimensional equivalent to pixels, say pix, then 1pixel = 1pix^2, and then 1 megapixel = (kpix)^2
      • perching_aix 1y ago
        After putting significantly more effort than perhaps socially acceptable into this, I completely agree so far, but I'm still horribly confused about GP's point about "mega" being a "squared unit in megapixels". That to me implies that "mega" in "megapixels" is a planar ("[pre?-]squared") scaling factor, but it's... not really? Are those even a thing? I think this is what the debate is about at least. Mega does line up with kilo squared, but that's not because mega becomes a planar scaling factor, but because it just so happens that 1000 times 1000 is 1 million. It's kind of a coincidence? Like it's literally 1 million pixels, that's what's being meant. Just like with cm squared, the ohhhhhhhhhhhhhhhhhhhhhhhhh
• waffletower 1y ago
  This is an armchair rant with a very narrow complaint. The decibel unit has objective utility in both analog and digital signal processing and the field of audio engineering. It is far from meaningless in filter design and a useful reference for software and hardware interfaces that employ them.
• bsteinbach 1y ago
  The power vs voltage thing I think comes from the historical connection of dB to sensing waves. Because you can change impedance to match any sensor, but power is conserved, power was just more often more important to discuss than voltage. I still have to look it up every time whether 10x is 10 or 20 dB.
• vt240 1y ago
  I see dB scale units used without contextual issues in near uniformity. Unfortunately, I have to agree with the OP, that microphone capsule manufactures seem to be an edge case. I'm not sure where dBV/Pa became the standard. I can understand why given 94dBSPL@1000Hz calibration standards, and the measurement equipment of the time, but I've run into my own fair share of datasheets with lines such as 'Sensitivity -45dB' with no units or other call outs for the standard in use. Thankfully, it seems like most modern datasheets use mV/Pa which seems like a much better unit in my book.