Interesting Papers re temporal resolution Options

[ncdrawl]

http://www.physics.sc.edu/kunchur/Acoustics-papers.htm

http://www.physics.sc.edu/kunchur/papers/FAQs.pdf

[John_Siau]

From the summary paragraph in "Audibility of temporal smearing and time misalignment of acoustic signals" by Dr. Kunchur

These qualitative and anecdotal observations point to the possibility that human hearing may be sensitive to temporal errors, τ , that are shorter than the reciprocal of the limiting angular frequency [2πfmax]^−1 ≈ 9 μs, thus necessitating bandwidths in audio equipment that are much higher than fmax in order to preserve fidelity.

Again, the same glaring error:

The Nyquist frequency does NOT determine the temporal resolution of a PCM system. The entire premise of the paper is fundamentally flawed. The experiment proves the need for moderately controlled jitter but does not establish the need for higher sample rates.

[Axon]

From the summary paragraph in "Audibility of temporal smearing and time misalignment of acoustic signals" by Dr. Kunchur

These qualitative and anecdotal observations point to the possibility that human hearing may be sensitive to temporal errors, τ , that are shorter than the reciprocal of the limiting angular frequency [2πfmax]^−1 ≈ 9 μs, thus necessitating bandwidths in audio equipment that are much higher than fmax in order to preserve fidelity.

Again, the same glaring error:

The Nyquist frequency does NOT determine the temporal resolution of a PCM system. The entire premise of the paper is fundamentally flawed. The experiment proves the need for moderately controlled jitter but does not establish the need for higher sample rates.

That seems too harsh to me - I agree that Dr. Kunchur is making huge conceptual mistakes with his treatment of digital audio, and in a lot of other things for that matter, but the experiment itself can't be dismissed so easily. Despite all the issues I have with the paper that I mentioned earlier, isn't it at least plausible on some sort of a priori level that, if one can guarantee a distortion of fairly reasonable consistency (internal to the ear), that testing of ultrasonics on that basis may be reasonable?

[2Bdecided]

That seems too harsh to me - I agree that Dr. Kunchur is making huge conceptual mistakes with his treatment of digital audio, and in a lot of other things for that matter, but the experiment itself can't be dismissed so easily. Despite all the issues I have with the paper that I mentioned earlier, isn't it at least plausible on some sort of a priori level that, if one can guarantee a distortion of fairly reasonable consistency (internal to the ear), that testing of ultrasonics on that basis may be reasonable?

Well, that's the whole point - but this flawed experiment didn't probe this properly - and all previous proper experiments show that, apart from via bone conduction, ultrasonics don't distort to create audible frequencies in the ear.

In equipment, yes, but not in the ear.

If someone proves otherwise (quite possible), it'll be interesting.

IIRC there was someone here who did (playing ultrasonic from a separate audio system(!) and ABXing presence / absence in the presence of an audible sound), but I didn't see how the thread ended.

Cheers,
David.

[rpp3po]

I'm just coming back from vacation. Thanks for the many insightful posts, I have just learned a lot! Until now I always thought that PCM being bandwidth limited and requiring low pass filtering is just about frequencies that no human ear would care about anyway and no big deal else.

Comprehending that the plot of a properly encoded PCM bitstream of a square wave is not square, why low passing before ADC is so important, and why perfect square waves don't fit into PCM in theory took me a big leap forward.

I had already checked DVD-A prices for my favorite records online... But until I see Kunchur refuting some of this thread's objections I'll stay as happy with Redbook as I always have been.

This post has been edited by rpp3po: Aug 2 2009, 19:09

[Arnold B. Kruege...]

But until I see Kunchur refuting some of this thread's objections I'll stay as happy with Redbook as I always have been.

As you seem to be saying, there's a lot of interesting twists along the way, but getting back to basics is very often a good thing.

Setting up a proper listening test that shows that high sample rates do make a difference with music is simpler and less costly than ever.

There is now a ton of high sample rate audio kicking around for free or not much money. Actually setting up the experiment can be accomplished with not only reasonably-priced buyware, but even with freeware.

There seems to be only one minor thing lacking - a pair of ears that produce results that are positive for high sample rates.

Whenever we see a paper like Kunchur's, we need to get back to basics. The basics are that just about anybody who wants to can set up a reliable listening test involving readily-available musical program material that has the potential to produce a positive outcome. Nobody seems to be able to do it. Instead, all we get are these abstract tests like Kunchur's, involving some most definately non-musical waveforms with questionable relevance and inconclusive results.

[rpp3po]

Nobody seems to be able to do it. Instead, all we get are these abstract tests like Kunchur's, involving some most definately non-musical waveforms with questionable relevance and inconclusive results.

I agree. Not a single positive result in a decade is simple but mortgageable evidence.

This post has been edited by rpp3po: Aug 3 2009, 01:46

[ncdrawl]

Nobody seems to be able to do it. Instead, all we get are these abstract tests like Kunchur's, involving some most definately non-musical waveforms with questionable relevance and inconclusive results.

I agree. Not a single positive result in a decade is simple but mortgageable evidence.

Dr. Kunchur will be posting confutations in form of FAQ updates...will be doing that regularly.

Apparently he has been bestowed with a great deal of common sense to go with his impressive educational credentials... IE he avoids online arguments. Very smart decision.

[honestguv]

> Dr. Kunchur will be posting confutations in form of FAQ updates...will be
> doing that regularly.

That will be interesting to see if he keeps digging himself deeper into a hole or starts trying to climb out. Unless he is a completely lost in audiophile belief (he is clearly a believer) he must have twigged by now that his lack of understanding of the information contained in a set of samples has lead him to make a bit of a fool of himself among his peers. But he is getting attention from the audiophile community. So which is more important to him? We will see.

> Apparently he has been bestowed with a great deal of common sense to go with
> his impressive educational credentials...

Why do you find them impressive? If you find scientific credentials impressive, why do you discard the bulk of relevant scientific work on sound perception performed by people with a higher standing in the field than your good Dr.?

> he avoids online arguments. Very smart decision.

In his position it would be rather unwise to do otherwise.

[andy_c]

Regarding my earlier post about the lack of second harmonic data in the "Temporal resolution of hearing probed by bandwidth restriction" article, it looks like he published those data in another article, "Probing the temporal resolution and bandwidth of human hearing" (PDF file here). I had previously used the number 1e-3 for the second harmonic relative to the fundamental, read from his graph in figure 4 of "Temporal resolution of hearing probed by bandwidth restriction", to compute the required accuracy for the duty cycle of the square wave. His actual tabular data show a second harmonic relative to the fundamental of 0.0003, or -70.4 dB, rather than -60 dB as I had originally read from his graph. Plugging in the numbers, the previous requirement for the duty cycle accuracy, which was 50 +/- 0.032 percent, now becomes 50 +/- 0.0095 percent for a -70.4 dB second harmonic. That assumes zero second-order distortion in the buffer that follows the square wave generator, the buffer after the LPF, the headphone amplifier, the headphones themselves, the microphone, the mic preamp, and the 12-bit A/D converter in the oscilloscope used to digitize the data. I've worked with test equipment for many years, and in all that time I've never seen a square wave generator specified for its second harmonic content. The specifications for the pulse generator he used certainly don't show anything like that. I suppose it would be possible to put it in the variable pulse width mode and adjust its parameters to minimize the second harmonic, but according to Axon's communications with Dr. Kunchur, the spectrum computation takes days(?). That would make such an approach impractical. Or it could actually be that the square wave symmetry of the generator is that good. It seems unlikely though.

On the plus side, as long as this ratio were low enough, and constant with varying bandwidth, it probably wouldn't influence the results at all. The very low values of second harmonic just jumped out at me, considering how tiny errors in duty cycle of the square wave (and other contributors to errors in half-wave symmetry) result in non-negligible second harmonic spectral content, as well as how the actual data for the second harmonic depend on unspecified parameters of the square wave generator. Also, the second harmonic data in figure 4 of "Temporal resolution of hearing probed by bandwidth restriction" looks like a noise blip, rather than having a wide baseline as the other harmonics do - which also looks odd. I suppose this could be due to the resolution limit of the 12-bit converter used in the scope.

This post has been edited by andy_c: Aug 3 2009, 18:27