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I found an audio file that's confusing me. This audio clip sounds like a distorted mess, which makes sense, but the volume is consistent, even on the low amplitude parts of the waveform. The two screenshots are of the same section of audio with one zoomed way in on the y-axis. What could be going on here? I tried normalizing the audio and the results were the same, so it isn't a result of clipping, and I've put the file into multiple editors and the waveform looks the same.

EDIT: A comment says that the volume sounds how you'd expect it to from the waveform using a different audio editor, so I guess I was somehow doing it wrong.

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Screenshot from Audition, waveform and spectral display

Zoomed in screenshot

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    @Mark It's a sound effect from a testing program for a video game. It's not corrupt. Feb 15, 2022 at 10:33
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    & define "volume is consistent". Are you playing this on a loop? Bear in mind it's 63ms long, that's about the length of a single cough. Inside that time essentially it switches a crunchy pseudo white noise on & off 5 times. It's not really surprising you're not fully perceiving the gaps.
    – Tetsujin
    Feb 15, 2022 at 22:12
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    What I'm looking to understand is how it's possible that there's volume being played during a section with a flat waveform. I slowed it down and the volume of white noise is the same even during the gaps. Feb 16, 2022 at 17:41
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    How are you slowing it down? Time stretch seems to get confused & tries to smooth out the wave - which ends up sounding something reminiscent of Wire's 'I am the Fly' - youtube.com/watch?v=OnIXXe83fe4
    – Tetsujin
    Feb 17, 2022 at 9:14
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    Just listened to it and had a play in Cubase - it has some loud bits, and some quiet bits - exactly as expected from the waveform screenshots you posted. So I cannot understand the problem - please add more detail/explanation
    – Rory Alsop
    Feb 17, 2022 at 18:04

1 Answer 1

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It's completely normal, there's nothing wrong with the audio, the editors or you!

Basically: You zoomed in too far 0_0

However...

These cyclic intervals of relatively low amplitude (I'll call 'gaps' from here in) are pretty close to 5 ms in length. The period of high and low amplitude starting at 0.015 seconds is close to 10 ms in length. There are 4 of these periods all together, taking ~40 ms. These are very small periods of time. The peaks do pass 0 dB, so you should get it down to around -3 dB to be sure you're not hearing any clipping, but, I don't think that has any particular relevance here. I think this is more to do with the length of the gap and the type of sound.

A 5 millisecond gap seems like a very small gap, so should you be able to hear it...?
Well, why not...? The pop of a balloon in an anechoic chamber lasts from between 1 and 3 ms. Down to a fifth of the length of the gaps, and you can hear it clearly.

Here's an example:

But there are other factors to take into account:

  1. I'll get the impossible mechanics bit out of the way first. The movement of the speaker diaphragm can't perfectly replicate the wave you see on your screen. There will be, amongst other things, longer transition times. Put simply, we're talking 5 thousandths of a second here for the diaphragm to stop moving, before the next period of high amplitude starts.
  2. Perception - It's hard for your brain to distinguish changes in sound at those lengths.
  3. I think this is the most important factor. Sound has a temporal masking effect in your auditory system, and sound with a 'white noise' quality is better at it. So this masking phenomenon makes it very difficult to perceive gaps of such a short length in any sound, but more so in sounds with a 'white noise' quality. This masking effect can reportedly stretch to 100 ms. That's 20 times longer than the gaps.

Listen closely...

That being said, are you sure you can't hear the gaps? Try listening closely through headphones. You should be able to hear a rapid fluttering (like a very fast tremolo). Maybe because of my decades creating and listening to strange sounds like this, maybe not, but I get the sense there are gaps in it. Perhaps my brain infers the presence of gaps through these rapid fluctuations and past experience tells it that gaps are most likely to be the cause, but I can definitely hear something like gaps.

Interestingly, seeing and listening to this audio clip has allowed me to perceive how long 5 ms really is. I took it for granted that that wasn't possible. Perhaps audio is the answer to perceiving very short lengths of time. ...But I digress!!

100 Hurts!

In a more analytical tone, this seems to be something close to white noise (potentially something distorted out of existence) which seems to have had amplitude modulation applied to the middle part using a 100 Hz square wave as the modulator signal. This will create a good bit of chaos in the output, but as there's no definite harmonic content, it wouldn't be notable to the listener, because...
white noise + white noise = white noise
white noise - white noise = white noise
That's my simple interpretation of the waveform.

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