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Upsamplers, DACs, jitter, shakes and analogue withdrawals, this is it.

RE: That clears up a lot!

Tony:

Well, now I see what you mean by "calibrated".

I'm not going to claim to be a "research scientist" in the sense you use the term, but the technique we used in these experiments is the standard one used by career research scientists to detect audible differences; it was correctly applied; and whether the audiophile community likes it or not, it is accepted as differentiating between real and imagined effects. You are right -- it was difficult and time-consuming to set up our experiments properly and eliminate spurious results.

It shouldn't have to be repeated after all this time, since this is in the paper, but I'll say it again: We did find detectable differences in some material -- with one particular production, recorded in extremely quiet surroundings, with microphones and electronics of sufficiently low noise involving material of very wide dynamic range so that the noise floor was below -92 dBA re full scale -- when we listened at elevated gain settings. (The gain, and the settings necessary to produce these positive results, are outlined in the paper.) Under these circumstances the noise in the CD-quality link became audible (as elevated hiss) and our test showed this easily. I have since found a couple of other recordings where this can be done, by using the player's A-B repeat feature in a segment that contains a long enough rest.

Perhaps it would be more useful for us to do another series of experiments and determine more precisely the gain threshold at which this occurs, since it is the only positive result we found. As a preliminary estimate I can tell you that the gain was about 8-10 dB above our chosen reference level. Of course it was strongly dependent on the background noise level in the room, and positive results at the gain I mentioned require an unusually high degree of isolation from external noise contamination. (If you have a refrigerator running two rooms away you may have to unplug it.) And once the music reached anything near normal recorded levels e.g. a mezzo-piano or above, the CD link was no longer detectable.

This is completely predicted by existing and long-accepted theories of digital encoding, starting with Claude Shannon's work in 1948, so it is not likely to impress the audiophile community very much. The idea that there should be audible differences on music at normal recorded levels is actually a radical notion, and as such it requires unusually strong proof. We made a thoroughgoing and sincere attempt to find any such effects using good equipment and trained listeners, and came up dry, with the above-named exception.

So it is true that we did not conclusively disprove the null hypothesis, but I believe your analysis is illogical, because it does not allow for the possibility that there are no audible effects at normal levels. You say we are incompetent because we didn't measure these and specify their threshold of audibility. What if they aren't there, as theory predicts? The "test material with known degradations" we should have used -- what would those degradations be, besides the added noise we did detect? I am open to suggestions. -- E. Brad Meyer

P.S. Who is Doctor Kunchur, and where can his written work be found?


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