44.1 vs 88.2 ABX report at AES
Reply #82 – 2010-08-09 21:41:12
I finally found time to read the entire paper. It's quite well written in my opinion, but there are three points I'd like to add to the discussion by krabapple and hciman77.Different clocks were used for the 88.2 and 44.1 kHz recordings (RME ADC internal clock for 44.1, external Mutec master clock for 88.2). So the recordings were actually not done with the "exact same audio gear and settings", as claimed. I wonder if, since 88.2 = 44.1 x 2, it would be possible to construct a master clock which can serve both sampling rates simultaneously, i.e. a clock with two outputs, and one output providing only every second clock pulse? Maybe Arnold, Werner, or some other knowledgeable person can comment on that. The paper doesn't specify how precise the delay alignment was for the ABX of the excerpts with different sampling rates, just this: "We made sure that the selected files at 44.1 kHz and 88.2 kHz had the exact same fades (in and out) and length." I guess it doesn't matter, though, since switching sampling rate upon playback supposedly introduced a significant pause. The procedure of separating the 3 listeners who "significantly selected the wrong answer" from the rest sounds highly questionable to me. I think that, in order not to introduce bias, you'd also have to exclude the 3 listeners (or in general, the same right-hand percentile) who significantly selected the right answer. Or even better: don't separate the 16 listeners at all ! Luckily, this was actually done by the authors. Their report: "When collapsing over all 16 participants, the results of the comparison between Orchestra files recorded at 88.2 and 44.1 kHz is still significant, p = .01. Concluding from the figures in the paper, I can add with confidence: When collapsing over all 16, the other two significant results (Guitar and Voice excerpts) disappear. Which leaves us with: a difference between different recording sampling rates (and different clocks) was heard on the Orchestra item with a significant level of confidence. Which is interesting. The authors themselves speculate that this might be due to more detailed reproduction of transients in case of high-resolution sampling rates, which seems to be in line with our own 20-kHz brick wall test and which leads me to the question: Amandine, would you mind sharing the low- and high-resolution Orchestra excerpt? Comments welcome Chris