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RE: Question RE: Atkinson - DBT/Absolute Signal Polarity

Trying to follow this is getting confusing. I'll try to shed some light on it, but I'm still not able to completely unravel the situation. Here's what I have so far.

I was able to dig up one of the references cited in the Stereophile article mentioned by bjh above. That reference is:

"On the Audibility of Midrange Phase Distortion in Audio Systems" (with John Vanderkooy and Mark Pocock), JAES, Vol.30 No.9, September 1982

I don't have access to the BAS publication referenced in the Stereophile article, only AES articles.

Part of the confusion is that the Lipshitz AES article is concerned with the audibility of the nonlinear phase response caused by all-pass filters such as what result when the high-pass and low-pass outputs of a Linkwitz-Riley loudspeaker crossover are summed. Absolute polarity is not the subject at all, but it is mentioned briefly in passing. Here is what I believe to be the relevant quote from the Lipshitz paper:

"The authors have demonstrated the two-tone experiment described above to numerous people on different systems. No one has ever failed to hear the timbral change with phase, and discern the polarity reversal on this signal with unvarying accuracy. Indeed, in a double-blind demonstration to eleven members of the SMWTMS audio group [13], the accuracy score was 100% on the summed 200-Hz and 400-Hz tones over loudspeakers, and overall, including musical excerpts, the results on the audibility of the polarity inversion of both loudspeaker channels were 84 correct responses out of 137, this representing confidence of more than 99% in the thesis that acoustic polarity reversal is audible."

So it can be seen that this test was apparently a mixture of musical excerpts and the test signal, not just music alone. The reference [13] is as follows:

B. F. Muller, "Third World: The Scientific Subjectivists," Audio Amateur, vol. 11, p. 64 (1980 Jan.).

I'd love to get this article if anyone has it. It's not at all clear to me whether Lipshitz had anything at all to do with the tests in that article, or if he's just referencing somebody else's results. Some other questions arise from this also, namely, "What fraction of the tested samples were 'musical excerpts'?", and "How did the individual scores on music and test tones break down?".

It looks like those questions can be answered by the info on the ABX site . These are broken down as follows:

Test signal: 24 / 24 = 100%
Music: 60 / 113 = 53%

These numbers match up with Lipshitz's reference of 137 total trials.

So this brings us to the statement made by John Atkinson in the referenced article, which I quote below.

"Work by Stanley Lipshitz in the late '70s (footnote 9), using carefully organized double-blind testing, confirmed that a reversal of absolute signal polarity will be subtly audible on music to a 99% confidence limit!" (Italics by JA).

Footnote 9 is as follows:
Footnote 9: "A little understood factor in A/B testing," The BAS Speaker, March 1979, followed by "On the Audibility of Midrange Phase Distortion in Audio Systems" (with John Vanderkooy and Mark Pocock), JAES, Vol.30 No.9, September 1982

The second reference in Footnote 9 is the Lipshitz article I quoted above. What's missing here is the BAS Speaker and Audio Amateur articles.

Even though I don't have all the pieces of the puzzle, I do have enough information to conclude that the statement in the Stereophile article referenced above is a misrepresentation. That was what TSP's point was in a post that has unfortunately been deleted.


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