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Music servers and other computer based digital audio technologies.

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RE: The beans have been spilled!

Posted by Tony Lauck on April 29, 2012 at 10:00:50:
What I figured. After forming my opinion by listening I did a simple test to see if the files were different, I used FLAC compression and noticed a slightly different file length in the compressed files. This peaked my curiosity so I did a null test with Soundforge and uncovered the differences.
Interestingly, the last time I tried listening to differences in dither at the 24 bit level (-139 dB) I was unable to hear them, but respected the reports, however implausible, by people like Charles Hansen and Romy the Cat that these differences were audible. Now with new speakers and amplifiers it was possible to hear differences at this level, but I doubt very much it would have been possible for me to pass an ABX test.
I preferred A over B. After playing A (and recognizing the recording as familiar) I played B and experienced the "entire soundstage collapsing," the "recording being completely trashed," etc.. Unfortunately, after switching back and forth a few times (as would have been necessary to obtain statistical significance in a blind test) everything started sounding the same, although perhaps the cymbal crash was still different. I have found this effect every time when doing repeated AB comparisons. I suspect it's a case of acoustic memory filling in the differences. (A few years ago one of the dCS people discussed the memory effect and its effect on blind tests at an AES seminar in London that had been on the web for a while.)
I am not convinced that I and others are hearing differences in sound at the -139 dB level. IMO it is more likely that one is hearing differences in artifacts created by one's DAC, which may create greater differences in the analog output. If one wanted to prove this speculation it would be possible (but difficult) to do this by using two DACs and mixing their analog output, feeding one with the original music for both A and B while feeding the other with zeros or the dither signal as appropriate. Both types of DAC (ladder and sigma-delta) have artifacts. Ladder DACs magnify small differences if their resistor values are not exactly correct. Sigma Delta DACs are affected by the chaotic operation of their modulators, which exhibits sensitive dependence on the input. It may be that the average differences are, indeed, at -139 dB but it does not follow that there won't be short term variations at much higher values. If this test proved that people could hear differences a further test would be required using completely separate DACs, amplifiers and speakers for the music and dither signals before one could reasonably conclude that people were hearing these differences instead of system artifacts.