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RE: Better duck under that desk;

Posted by Ryelands (A) on August 5, 2009 at 07:59:20

In Reply to: RE: Better duck under that desk; posted by Werner on August 4, 2009 at 04:13:36:

werner wrote:

I hope this clarifies things a bit.

Thanks for your note and sorry for the late reply but, no, I’m afraid it doesn’t entirely clarify things for me.

Yes, they can be resolved . . . The theoretical limit on the time resolution of a sampled quantised system is the sampling period divided by the number of quantisation steps (I may be off with a factor of 2).

Unfortunately, I cannot translate that into the “μsecs” on which Kunchur bases his argument. Can you help?

The third harmonic of 7k is 21k. If the auditory system is sensitive (in some unknown way) to sound above its nominal cutoff frequency, then surely this 21k would figure heavily in the detection process. But the thing is: 21k can be passed by 44.1kHz sampled systems.

1. Your argument seems to assume that RBCD recordings are made to (and DACs operate at) these theoretical limits. This seems optimistic: as I understand it, upper limits are, in practice, significantly lower than 22 KHz because the Nyquist filters are not, by design, “brickwall”.

In other words, are you sure that 44.1 KHz systems can, and in practice do , resolve (pass) 21 KHz? If they do, your point is fair. If they don’t, it isn’t. My guess is that they very often don’t.

2. In any case, Kunchur’s data seem to have undermined the argument already.

In his 2008 paper ( Temporal resolution . . . ), he measured the HF threshold of a group of subjects with the two best coming in at 17.7 and 17.8 KHz. The poorest, on the other hand, only got to 9.4 KHz and would thus have been struggling a bit with the 8 KHz tone, never mind overtones (see below).

In spite of that, he/she scored 100 per cent for t = 5.6 μsec, the second lowest value to provide a significant result over the group as a whole. (See Experiment 1 and Table 3.) In other words, he/she was pretty well up there with the best of them in spite of significant hearing loss. That suggests, and Kunchur’s text makes it explicit, that the results are not down simply to the audibility of harmonics.

So the 7k test cannot prove (contrary to K's claim) that 44.1k is insufficient. On the other hand, if people pass an 8k test (which was not tried), and if the detection mechanism involves the third harmonic (which we don't know), then 44.1k is proven to be insufficient.

As I read the text, Kunchur demonstrated that all the harmonics of the test tone were inaudible (Table 1 & p 597).

2) The first intermodulation product of 7k and 21k is 14kHz. Many people still hear 14k. The first intermod prod of 8k and 24k is 16k. Many people don't hear 16k anymore. If the auditory system uses the level and phase of this intermod product for detecting the differences experimentally tested by K, then the outcome of such test would differ drastically between 7k and 8k.

As I have explained, this argument does not seem to accord with the data.

If you were to say that Kunchur makes a conceptual leap when he argues that his experiment conclusively proves that 44.1 KHz sampling rates are inadequate, I’d probably agree with you. But the argument that using an 8 KHz test tone in preference to a 7 KHz one would have proved the argument unequivocally does not, it seems to me, hold much water.

And if it does, it leaves the task of explaining why so many competent observers are adamant that higher resolutions provide better reproduction. (Higher resolutions for recording is, of course, a different thing.)

Dave

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