4 ms·

> 1000Hz @ 0dB (this only makes sense if you're a phone person) Any phone people here?

LegitShady 5y ago
https://en.wikipedia.org/wiki/Milliwatt_test https://en.wikipedia.org/wiki/Milliwatt_test https://en.wikipedia.org/wiki/Loop_around https://en.wikipedia.org/wiki/Loop_around I'm not a phone person but I've heard of this before.
- pimlottc 5y ago
  TIL 0 decibels ≠ silence
  - pxx 5y ago
    Decibels are only ever a relative measurement on a logarithmic scale. In this case, we aren't even talking about sound (these are dB of power), but this is true independent of base unit. For sound, to represent silence, you actually need -∞ dB. The fact that this is a relative scale is also why your mixer/home theatre receiver represents full intensity as 0 dB and any volume adjustments as some negative number of dB (some mixers may allow you to go a little bit over 0 dB but of course this risks clipping when a full-strength signal comes in). Fun fact though: the sound scale is capped on the upper extreme depending on your environment. You know how recordings of launches of rockets sound like the sound is clipping? It's not hardware limitations. The sound is actually clipping as the pressure hits vacuum. See https://en.wikipedia.org/wiki/Sound_pressure#Sound_pressure_level https://en.wikipedia.org/wiki/Sound_pressure#Sound_pressure_... .
billwear 5y ago
A 0dB tone is a tuning tone. Most amplifiers are tuned to a particular frequency at 0dB, and with a good phone connection, you can even do this over the wire. It's problematic if there are too many hops between you and the source. For example, calling a 0dB tone in a small CO in central Montana didn't give me a usable reference when I was calling from Huntsville, AL, in the 1970's. There were about four hops in there.
- myself248 5y ago
  It was originally 1000Hz, but it turns out this could cause framing errors on D4 trunks because the framing recovery circuit could misidentify the bit pattern as valid framing bits. So they changed it to 1004Hz, enough to sidestep the problem, but still close enough that it would still represent "exactly" a milliwatt of energy, within the required precision of the instruments anyway. When ESF framing was invented, precise tones no longer posed a problem, but a lot of D4 trunks hung around for decades, so last I checked most milliwatt tones were still 1004Hz.
zikduruqe 5y ago
Where's my DS0 folks at? I used to tune my channel bank cards to 1004Hz at 0 db. μ-law for the win.

https://en.wikipedia.org/wiki/Milliwatt_test https://en.wikipedia.org/wiki/Milliwatt_test https://en.wikipedia.org/wiki/Loop_around https://en.wikipedia.org/wiki/Loop_around I'm not a phone person but I've heard of this before.

pimlottc 5y ago
TIL 0 decibels ≠ silence
- pxx 5y ago
  Decibels are only ever a relative measurement on a logarithmic scale. In this case, we aren't even talking about sound (these are dB of power), but this is true independent of base unit. For sound, to represent silence, you actually need -∞ dB. The fact that this is a relative scale is also why your mixer/home theatre receiver represents full intensity as 0 dB and any volume adjustments as some negative number of dB (some mixers may allow you to go a little bit over 0 dB but of course this risks clipping when a full-strength signal comes in). Fun fact though: the sound scale is capped on the upper extreme depending on your environment. You know how recordings of launches of rockets sound like the sound is clipping? It's not hardware limitations. The sound is actually clipping as the pressure hits vacuum. See https://en.wikipedia.org/wiki/Sound_pressure#Sound_pressure_level https://en.wikipedia.org/wiki/Sound_pressure#Sound_pressure_... .

billwear 5y ago

A 0dB tone is a tuning tone. Most amplifiers are tuned to a particular frequency at 0dB, and with a good phone connection, you can even do this over the wire. It's problematic if there are too many hops between you and the source. For example, calling a 0dB tone in a small CO in central Montana didn't give me a usable reference when I was calling from Huntsville, AL, in the 1970's. There were about four hops in there.

myself248 5y ago
It was originally 1000Hz, but it turns out this could cause framing errors on D4 trunks because the framing recovery circuit could misidentify the bit pattern as valid framing bits. So they changed it to 1004Hz, enough to sidestep the problem, but still close enough that it would still represent "exactly" a milliwatt of energy, within the required precision of the instruments anyway. When ESF framing was invented, precise tones no longer posed a problem, but a lot of D4 trunks hung around for decades, so last I checked most milliwatt tones were still 1004Hz.

zikduruqe 5y ago

Where's my DS0 folks at? I used to tune my channel bank cards to 1004Hz at 0 db. μ-law for the win.