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In Reply to: Temporal resolution and RBCD posted by cics on July 28, 2009 at 13:22:50:
cics wrote:Indirect perception of ultrasonics is not in dispute.
Maybe not in “audiophile†circles but what is striking about Kunchur’s papers is that they present a meticulous demonstration of the phenomenon in mainstream journals.
I don’t know if his findings are disputed but they will certainly have surprised many. Less surprising is that he had to build apparatus to unprecedented levels of accuracy (OK, unprecedented in psycho-acoustic circles) to make his discoveries. As he explained to the Acoustical Society of America (see TL’s link), this was not a trivial exercise:
An enormous time (of the order of two years) and effort were spent to develop the instrumentation and the methods for checking for artifacts. For example, for just the Fourier spectrum shown in Fig. 4, it took a few months to develop the instrumentation setup and to write the C code (FFT was not used). To measure one such spectrum takes over a week. Notice that the noise level is below 0 dB SPL. Without performing such tests, it will not be known exactly what frequency components are present and what their roles are in the discernment. To simply trust the instructions given to a signal synthesizer and expect that that is what actually comes out is risky.cics then wrote:
However, a similar time resolution is observed by displacing the speaker [snip] In this test the low pass filter remains unchanged (i.e. we have the same ultrasonic information presented) but differences down to 6 μs are observed (through speaker time alignment changes).
As I understand it, the two experiments are essentially the same except that in the one the signal is modulated by varying the time constant of a filter (by altering R1 in fig 5 of the AAS paper - see the main paper for details of how it was done) and in the other by altering the horizontal alignment of two ribbon tweeters (Distance d in fig 6 of the AAS paper. See also figs 3 and 7.)
In his “FAQâ€, Kunchur writes of RBCD recordings:
If there are two sharp peaks in sound pressure separated by 5 microseconds (which was the threshold upper bound determined in our experiments), they will merge together and the essential feature (the presence of two distinct peaks rather than one blurry blob) is destroyed. There is no ambiguity about this and no number of vertical bits or DSP can fix this . [Emphasis added]So when cics writes:
The paper’s conclusion that such high recording bandwidth and format is required for full fidelity is not clear . . .
I beg to differ. It seems pretty clear to me. And later, when he writes:
By upsampling 44.1k to 192k we increase time resolution from 22.7 μs to 5.2 μs [snip . . . ] with correct upsampling (i.e. bandlimited interpolation) we can get very close
he seems to me to be contradicting Kunchar’s basic point that information, once lost, is gone forever. Upsampling RBCD may or may not be preferable to NOS - and cics has consistently presented a strong case that it is - but that is a different debate.
Kunchar has demonstrated that humans can, at least under highly contrived laboratory conditions, perceive tiny details that 44.1 kHz recordings are, unarguably, unable to capture.
Rightly, in my view, he doesn’t extrapolate from that to generalisations about how we perceive music but he does make a strong case for distributing recordings via media that retain more original detail than is possible with the RBCD format.
Dave
PS A minor detail: the 96-year-old that Tony alluded to in his reply to Phelonoius Ponk was not in fact one of Kunchar’s subjects but a neighbour of audio journalist George Foster. He could apparently readily distinguish SACD from CD and vinyl recordings from digital ones.
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Follow Ups
- RE: Temporal resolution and RBCD - Ryelands 07/29/0904:37:17 07/29/09 (0)
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