4 ms·

Stripping frequencies above 20kHz negates the effect on the lower frequencies since those lower frequencies are not "modified" by the higher ones. The human hea

by cmer 15y ago

Stripping frequencies above 20kHz negates the effect on the lower frequencies since those lower frequencies are not "modified" by the higher ones. The human hear can actually hear the very high harmonics when they're combined with a lower fundamental frequency. For example, the human hear will hear a 30kHz frequency if it's fundamental is 10kHz. If it's played at 44.1kHz, the 30kHz frequency is gone and all you'll hear is 10kHz, not a "different sounding" 10kHz.

deleted 15y ago
[deleted]
Anechoic 15y ago
For example, the human hear will hear a 30kHz frequency if it's fundamental is 10kHz You are going to have to provide me with a citation to back that up because that goes against everything I've learned and experience in 17 years of working in acoustics.
- cmer 15y ago
  Humans will hear the impact > 20kHz frequency has on the lower frequencies, not the 30kHz frequency itself. That's been proven a million times.
  - surrealize 15y ago
    Note the lack of citation
    - pragmar 15y ago
      http://en.wikipedia.org/wiki/Overtones http://en.wikipedia.org/wiki/Overtones I don't know about the physics of the speaker itself generating the overtone (in cabinet), but it could certainly resonate a wine glass in the room, for example.
      - surrealize 15y ago
        Yes, overtones exist, and yes, overtones affect the sound, and yes, if you filtered the sound to remove overtones in the audible range then it would sound different. However, if you remove overtones outside the audible range then it will not make an audible difference (this is what xiphmont was saying in TFA). So no, your wikipedia link is not a citation for the claim that cmer made.
  - Anechoic 15y ago
    If you're not going to hear the frequency, then there's no reason to record it, so I don't see what you're objection is.
    - eatmyshorts 15y ago
      Yes, but if you sample the frequency to create a step wave, then neglect to filter the results, you will end up reproducing tons of high frequencies. That is why we need to filter the output for signals >20KHz...to remove these harmonics that result from reproducing the square wave. Of course, filters aren't perfect, and result in phase shift and roll-off. So we over-sample the signal to create a signal with a much higher frequency than 20KHz, so that the filtering occurs well outside the audible band, allowing us to filter out all of these harmonics without affecting the desired signal. Basically, the end result is that by sampling the signal, you are introducing high frequency content that must be removed prior to playback. This high frequency content is one of the reasons old CD players from the 80s and 90s cause "listener fatigue", although I have no sources to back up that last statement.
      - dedward 15y ago
        Yup... people need to get very clear in their heads the difference between the recording/sampling/mixing/mastering stages, where high bitrate/width/gear/knowledge is helpful, and playback, which is a completely different thing. (not for eatmyshorts -you get this I gather) - everyone gets that "upsampling" can't add detail to a recording right? You can't get more than you've got.... no matter what you do. There is no magic. You upsample so you drive harmonics generated in the digital-to-analog process during playback further up in the spectrum so when you get to the analog stage you can use a nice gentle analog filter to filter them out. Without the upsampling, you need a nasty steep analog filter to filter them out, and that can have audible side-effects (or at least measurable) in the audible spectrum. eatmyshorts - correct me if I mis-stated any of that please....
        eatmyshorts 15y ago
        You got it 100% correct. You upsample simply to move the frequency of the analog filter higher, with a gentle rolloff (and ideally a 1st order filter, so you introduce no phase effects) to get your final signal.
  - smallblacksun 15y ago
    >That's been proven a million times. Then you should be able to provide at least one citation.
  - shasta 15y ago
    In other words, your theory is that the superposition principle doesn't hold for sound waves.
    - kragen 15y ago
      Well, the superposition principle only holds in linear media. Sound waves can propagate in linear media, but they can also propagate in nonlinear media, and any medium that can carry sound will go nonlinear at sufficiently high amplitudes.
  - bigiain 15y ago
    If that is true, surely in your up thread example of recording a triangle, the "impact on lower then 20kHz frequencies" would already have happened during the recording process in between the triangle and the microphone, and would have been captured perfectly on recording equipment that's proven capable of capturing everything below 20kHz? So we'd "hear" the effect as part of the recording instead of requiring it to happen in our listening room…
  - CamperBob 15y ago
    "A/B or GTFO," I believe is the parlance of our times.
- runeks 15y ago
  It's definitely possible for two sounds to be indistinguishable when played separately, but when played together it is revealed that they are in fact different (see link below). Whether this applies for sounds with frequencies above 20kHz I don't know. I'd like to see a citation as well. Doesn't seem like it would be the hardest experiment to set up either. http://en.wikipedia.org/wiki/Cent_(music)#Sound_files http://en.wikipedia.org/wiki/Cent_(music)#Sound_files
  - SpiderX 15y ago
    Me and my brother would sing at each other in certain tones such that we created harmonics in both our ears. It wasn't pleasant, but it was interesting. Regardless, I'd smash my equipment if it made harmonics like that.
- eatmyshorts 15y ago
  Here is a Wikipedia article on the subject: http://en.wikipedia.org/wiki/Sound_from_ultrasound http://en.wikipedia.org/wiki/Sound_from_ultrasound Basically, if you produce two ultrasonic frequencies, they will create an interference pattern at a much lower frequency than either of the individual frequencies. Modulate a signal on the difference between two signals, and you can create a directional speaker, since ultrasonic sounds tend to be highly directional (so long as the diameter of the transducer is greater than 1/2 wavelength, which is almost guaranteed with ultrasonic signals). This is how the "sound cannons" that are being deployed for crowd control work.
  - pjscott 15y ago
    That's very cool, but it requires pretty high-intensity ultrasound to be noticeable. I doubt that will be the case with ordinary music.
  - Anechoic 15y ago
    That article describes hetrodyning which happens because ultrasonic frequencies at high amplitudes interacts nonlinearly with air. You are not going to see that effect with sound waves generated near the audible spectrum, and normal loudspeakers are going to generate ultrasonic sound waves.
    - eatmyshorts 15y ago
      Yes, but the effects of interference patterns between multiple ultrasonic frequencies is the same, and definitely does affect the audible spectrum. This is why we must filter the square wave that comes out of a DAC. And the limitations of filters (phase shifts and roll-off) are why modern CD players oversample the signal--so that the filtering can be performed well beyond the audible spectrum.
      - Anechoic 15y ago
        This: Yes, but the effects of interference patterns between multiple ultrasonic frequencies is the same, and definitely does affect the audible spectrum has nothing to do with this: This is why we must filter the square wave that comes out of a DAC The only reason that square waves "must" be filtered is to reduce the potential of damaging tweeters. If you want to record a square wave with the purpose of later reproducing the square wave, than you don't want to filter it - once you filter it, it's no longer a square wave.
- DanBC 15y ago
  Are they talking about "beat frequency" type effects?
  - qq66 15y ago
    Yes. A 40KHz tone and a 41KHz tone will interfere with each other and can create 1KHz tones that are audible. Edited to correct error, thanks anechoic.
    - Anechoic 15y ago
      No, Holosonics is not creating sound from beating, they are using heterodyning, which takes advantage of how high-amplitude ultrasonic sound waves interact with the atmosphere, that's different from beating.
    - nullc 15y ago
      They don't— the air is linear (except at insane sound pressures) so there is no interference. While the ear is not linear, it doesn't respond at those frequencies. If it really worked that way it would be trivial to demonstrate. Alas, it doesn't.
xiphmont 15y ago
> For example, the human hear will hear a 30kHz frequency if it's fundamental is 10kHz. No. It won't.
texel 15y ago
I think you're referring to this: http://en.wikipedia.org/wiki/Missing_fundamental http://en.wikipedia.org/wiki/Missing_fundamental Which, since it's a psychoacoustic phenomenon, wouldn't hold true when the partials involved are above the audible spectrum.
dedward 15y ago
I know where you're going with this I think, and I'm not disagreeing outright, but wouldn't this be captured during the high-bitrate (or good analog?) recording and mixing phase if the recording/mixing/mastering engineer were doing things right? At least, as well as possible?

by cmer 15y ago

deleted 15y ago

[deleted]

Anechoic 15y ago

For example, the human hear will hear a 30kHz frequency if it's fundamental is 10kHz You are going to have to provide me with a citation to back that up because that goes against everything I've learned and experience in 17 years of working in acoustics.

cmer 15y ago
Humans will hear the impact > 20kHz frequency has on the lower frequencies, not the 30kHz frequency itself. That's been proven a million times.
- surrealize 15y ago
  Note the lack of citation
  - pragmar 15y ago
    http://en.wikipedia.org/wiki/Overtones http://en.wikipedia.org/wiki/Overtones I don't know about the physics of the speaker itself generating the overtone (in cabinet), but it could certainly resonate a wine glass in the room, for example.
    - surrealize 15y ago
      Yes, overtones exist, and yes, overtones affect the sound, and yes, if you filtered the sound to remove overtones in the audible range then it would sound different. However, if you remove overtones outside the audible range then it will not make an audible difference (this is what xiphmont was saying in TFA). So no, your wikipedia link is not a citation for the claim that cmer made.
- Anechoic 15y ago
  If you're not going to hear the frequency, then there's no reason to record it, so I don't see what you're objection is.
  - eatmyshorts 15y ago
    Yes, but if you sample the frequency to create a step wave, then neglect to filter the results, you will end up reproducing tons of high frequencies. That is why we need to filter the output for signals >20KHz...to remove these harmonics that result from reproducing the square wave. Of course, filters aren't perfect, and result in phase shift and roll-off. So we over-sample the signal to create a signal with a much higher frequency than 20KHz, so that the filtering occurs well outside the audible band, allowing us to filter out all of these harmonics without affecting the desired signal. Basically, the end result is that by sampling the signal, you are introducing high frequency content that must be removed prior to playback. This high frequency content is one of the reasons old CD players from the 80s and 90s cause "listener fatigue", although I have no sources to back up that last statement.
    - dedward 15y ago
      Yup... people need to get very clear in their heads the difference between the recording/sampling/mixing/mastering stages, where high bitrate/width/gear/knowledge is helpful, and playback, which is a completely different thing. (not for eatmyshorts -you get this I gather) - everyone gets that "upsampling" can't add detail to a recording right? You can't get more than you've got.... no matter what you do. There is no magic. You upsample so you drive harmonics generated in the digital-to-analog process during playback further up in the spectrum so when you get to the analog stage you can use a nice gentle analog filter to filter them out. Without the upsampling, you need a nasty steep analog filter to filter them out, and that can have audible side-effects (or at least measurable) in the audible spectrum. eatmyshorts - correct me if I mis-stated any of that please....
      - eatmyshorts 15y ago
        You got it 100% correct. You upsample simply to move the frequency of the analog filter higher, with a gentle rolloff (and ideally a 1st order filter, so you introduce no phase effects) to get your final signal.
- smallblacksun 15y ago
  >That's been proven a million times. Then you should be able to provide at least one citation.
- shasta 15y ago
  In other words, your theory is that the superposition principle doesn't hold for sound waves.
  - kragen 15y ago
    Well, the superposition principle only holds in linear media. Sound waves can propagate in linear media, but they can also propagate in nonlinear media, and any medium that can carry sound will go nonlinear at sufficiently high amplitudes.
- bigiain 15y ago
  If that is true, surely in your up thread example of recording a triangle, the "impact on lower then 20kHz frequencies" would already have happened during the recording process in between the triangle and the microphone, and would have been captured perfectly on recording equipment that's proven capable of capturing everything below 20kHz? So we'd "hear" the effect as part of the recording instead of requiring it to happen in our listening room…
- CamperBob 15y ago
  "A/B or GTFO," I believe is the parlance of our times.
runeks 15y ago
It's definitely possible for two sounds to be indistinguishable when played separately, but when played together it is revealed that they are in fact different (see link below). Whether this applies for sounds with frequencies above 20kHz I don't know. I'd like to see a citation as well. Doesn't seem like it would be the hardest experiment to set up either. http://en.wikipedia.org/wiki/Cent_(music)#Sound_files http://en.wikipedia.org/wiki/Cent_(music)#Sound_files
- SpiderX 15y ago
  Me and my brother would sing at each other in certain tones such that we created harmonics in both our ears. It wasn't pleasant, but it was interesting. Regardless, I'd smash my equipment if it made harmonics like that.
eatmyshorts 15y ago
Here is a Wikipedia article on the subject: http://en.wikipedia.org/wiki/Sound_from_ultrasound http://en.wikipedia.org/wiki/Sound_from_ultrasound Basically, if you produce two ultrasonic frequencies, they will create an interference pattern at a much lower frequency than either of the individual frequencies. Modulate a signal on the difference between two signals, and you can create a directional speaker, since ultrasonic sounds tend to be highly directional (so long as the diameter of the transducer is greater than 1/2 wavelength, which is almost guaranteed with ultrasonic signals). This is how the "sound cannons" that are being deployed for crowd control work.
- pjscott 15y ago
  That's very cool, but it requires pretty high-intensity ultrasound to be noticeable. I doubt that will be the case with ordinary music.
- Anechoic 15y ago
  That article describes hetrodyning which happens because ultrasonic frequencies at high amplitudes interacts nonlinearly with air. You are not going to see that effect with sound waves generated near the audible spectrum, and normal loudspeakers are going to generate ultrasonic sound waves.
  - eatmyshorts 15y ago
    Yes, but the effects of interference patterns between multiple ultrasonic frequencies is the same, and definitely does affect the audible spectrum. This is why we must filter the square wave that comes out of a DAC. And the limitations of filters (phase shifts and roll-off) are why modern CD players oversample the signal--so that the filtering can be performed well beyond the audible spectrum.
    - Anechoic 15y ago
      This: Yes, but the effects of interference patterns between multiple ultrasonic frequencies is the same, and definitely does affect the audible spectrum has nothing to do with this: This is why we must filter the square wave that comes out of a DAC The only reason that square waves "must" be filtered is to reduce the potential of damaging tweeters. If you want to record a square wave with the purpose of later reproducing the square wave, than you don't want to filter it - once you filter it, it's no longer a square wave.
DanBC 15y ago
Are they talking about "beat frequency" type effects?
- qq66 15y ago
  Yes. A 40KHz tone and a 41KHz tone will interfere with each other and can create 1KHz tones that are audible. Edited to correct error, thanks anechoic.
  - Anechoic 15y ago
    No, Holosonics is not creating sound from beating, they are using heterodyning, which takes advantage of how high-amplitude ultrasonic sound waves interact with the atmosphere, that's different from beating.
  - nullc 15y ago
    They don't— the air is linear (except at insane sound pressures) so there is no interference. While the ear is not linear, it doesn't respond at those frequencies. If it really worked that way it would be trivial to demonstrate. Alas, it doesn't.

xiphmont 15y ago

> For example, the human hear will hear a 30kHz frequency if it's fundamental is 10kHz. No. It won't.

texel 15y ago

I think you're referring to this: http://en.wikipedia.org/wiki/Missing_fundamental http://en.wikipedia.org/wiki/Missing_fundamental Which, since it's a psychoacoustic phenomenon, wouldn't hold true when the partials involved are above the audible spectrum.

dedward 15y ago

I know where you're going with this I think, and I'm not disagreeing outright, but wouldn't this be captured during the high-bitrate (or good analog?) recording and mixing phase if the recording/mixing/mastering engineer were doing things right? At least, as well as possible?