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Comment by hamandcheese | Hacker News Reader

24/192 can capture audio well beyond what we can hear. These sounds can, though, lead to distortion that is within our hearing range, depending on the equipment used.

Therefore, rather than just being useless extra data, it can be actively harmful to the listening experience.

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It's not that much different to think of than 480p vs 4K/2160p -- dramatically higher resolution, increasing the width and length of the 'grid' that sound is recorded into -- except that in the case of audio fidelity, quality after a certain point causes problems with playback systems, resulting in audible artifacts and distortion.

That analogy works if you modify it:

- 480p vs 2160p is measuring the resolution of your cell phone propped up on a pillow at the other end of your living room

- experimental evidence shows that your eyesight is not good enough to pick up on the increased resolution, you've maxed out your sensory perception

- Your phone stutters trying to stream at 4k so the playback might actually be worse.

All good points! Indeed all that extra data makes the decode stage that much more difficult. Same happens with audio too, but high-res audio isn't nearly as bulky as video or nearly as resource-intensive to decode

very good analogy.

The analogy with images is demonstrated in this screenshot [1], which is referenced in a StackOverflow answer on the topic of image scaling in web browsers [2].

When the high resolution image is downscaled poorly, some high (spatial) frequencies are aliased down into lower (spatial) frequencies, manifesting as blocky/jagged lines. The images are 2D data in the spatial domain, while the audio is 1D data in the temporal domain, but the aliasing of high frequency signal to lower frequency artifact is similar.

Viewing a high resolution image on a panel that has enough pixels to display it without scaling is analogous to listening to 192 kHz audio on a fantastic speaker system that can reproduce those high frequencies accurately, instead of causing distortion by aliasing them to lower frequencies. On the other side, viewing a high resolution image which has been downscaled poorly is analogous to listening to that 192 kHz audio on a realistic speaker system that cannot reproduce high frequencies, which results in those signals aliasing down into the audible range.

And as you say, there is a point where, for the viewer/listener's sake, it doesn't make sense to push for higher frequencies because even if you can build a panel/speaker that will faithfully reproduce those frequencies without aliasing, the eye/ear will not be able to perceive the additional detail.

[1] http://www.maxrev.de/files/2012/08/screenshot_interpolation_...

[2] https://stackoverflow.com/a/11987735

Technically this is not aliasing; rather, the large and varied non-linearities of a speaker can act like a frequency mixer, which is why you'll get a 3 kHz sound (the difference) when playing, say, 20 and 23 kHz.

Increasing the bits doesn't increase the accuracy of the audio in terms of frequencies. It's 100% accurate regardless of bits. That's why trying to compare it to video resolution doesn't work. Bit depth is more akin to the screen brightness. If you turn down the brightness to 1 step from black, it's impossible to distinguish features in the image.

But weren't those "outside our hearing range sounds that can distort our hearing range" present in real life when the recording was made? So I would have heard the distortions had I been there in real life?

The problem is that your speakers were not designed to reproduce sounds at those frequencies, so instead of faithfully reproducing those sounds (that you can't hear anyway) they may emit unintended artifacts/distortion (that you can hear).

The distortions he's talking about would be introduced during playback by DAC, signal processing, speakers, or amplification.

The distortions are not present in the source. They occur because the speaker is a physical device subject to physical limitations and can't perfectly reproduce the waveform. In the process of trying to reproduce the ultrasonic signal, the speaker can produce audible distortions. If the ultrasonic signal is not there to begin with, then it can't possibly cause distortion.

I doubt that is the case. Most systems which I have used actually sound better at the higher sampling rates. This is not because the sampling rates cause anything to sound better, but because the hardware works better at those rates. In a blind test, you wouldn't be able to decide which one you liked better, only that there is a difference. At least on the machines I have, there are some clearly audible differences.

"In a blind test, you wouldn't be able to decide which one you liked better, only that there is a difference"

That would have to be the noise. The math doesn't lie...

I'm not talking about noise or other artifacts from the conversion process. I am talking about differences in bass and treble balance that come from different engineering in the converters at different frequencies. In some converters, there are actually completely different circuits that engage for different frequencies. The converters that I have experienced do this, and they all have a noticeable effect on what we hear.

> you wouldn't be able to decide which one you liked better, only that there is a difference.

Yet people have been reliably _unable_ to do this.

The gold standard in listening tests for this is an ABX where you are simply trying to show that you can discern a difference.

When properly setup and calibrated people are unable to show that they can distinguish 48kHz and 192kHz.

Moreover, by the numbers, audio hardware tends to work less well at higher rates if they're different, because running them at higher rates makes their own internal noise shaping less powerful. (Though for anything done well the distinction should still be inaudible).

Finally, if you do have cruddy converters that sound significantly different at different rates nothing stops you from using a transparent software resampler (SSRC is well respected for good reason) to put the audio at whatever rate you want.. until you get better hardware. :)

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