24/96 digitalization - can it be audible, blind test results Options

[pawelq]

I would like to share results of a blind listening test that was conducted on June 16th, 2011 in Warsaw, Poland.

The full description of the test is available at http://www.audio.e-snp.net/, but it’s in Polish, so I’ll provide a synopsis below.

The test question was "can we hear any effect of A/D/A conversion at 24/96 performed with a studio recorder". Frankly, both the test organizer and me (let's say, the test statistician), were pretty much convinced that no difference would be detectable.

The test music was played using a gramophone (Bergman Audio Sindre with Air Tight PC-1 cartridge), gramophone preamp (Air Tight ATE-2005), * , amplifier (Soulution 720 / 710), and loudspeakers (Hansen Audio Prince V2). In “analog” trials, the path was as described above. In “digital” trials, a studio recorder (Tascam DV-RA1000) set into “monitor” mode (i.e., A/D then D/A, at 24 bit and 96 kHz) was inserted in place of the asterisk.

The participants listened to about 1 minute of “Falling Alice” from Chick Corea’s “Mad Hatter” LP from 1976, mint condition. The test was conducted in a 5.8 m x 7.8 m acoustically adapted room.

There were 10 listeners (neither the test organizer nor me participated; he was switching the connections, I was several thousand kilometers away). All listeners listened together, being in the same room. They left the room for connection switching. During listening, the test organizer remained in the back of the room, invisible to the listeners. The listeners are (and me and the organizers) are members of a small Polish “sensible audiophile” internet forum.

There were 13 test trials, in 7 seven of them there was A/D/A conversion (D), in 6 purely analog path was used (A). The order of D and A trials was random.

Prior to the test, the listeners familiarized themselves with the supposed difference in A vs. D sound and with the recording, which was played a few times in A and D configuration. The listeners received answer cards on which they marked the trials as A or D. They were asked to answer in each trial, even if they were unsure. Prior to the test, they also provided answers to three questions: “Do you think that the effect of digitalization will be audible (yes/no)?”, “Do you consider yourself an experienced listener of vinyl records, using high-quality equipment (yes/no)?”, “How much of your listening time is spent listening to vinyl records (in %)”.

The results were analyzed in two main ways.
In the individual analysis, we checked if any of the participants identified A vs. D at a statistically significant level. With one-way binomial test with Šidák correction (due to multiple listeners. i.e., multiple tests) we determined that at most one error (12/13 correct) is allowed to pass this test (p=0.017; for 11/13 p=0.107).
In group analysis, we converted the results to proportion correct (e.g., 8/13=0.615) and used one-way Wilcoxon one-sample test to determine if the median of proportion correct was significantly higher than 0.5. (Additionally, we calculated one-way one-sample t-test, however, due to the small sample size, the normality assumption could not be reliably tested and we consider the results of t-test to be less trustworthy.)

The results table, a plot of proportion correct for each listener, and a more detailed description of the analysis are provided at http://www.audio.e-snp.net/wyniki.php (FYI, in the result table A stands for “analog” trials, C stands for “digital” trials, column 1 is listener number, columns 2-4 are answers to the three questions (NIE=no, TAK=yes), the bottom row shows what actually happened in the trials.)
No listener answered with 0 or 1 error, which was required for statistically significant outcome of the individual analysis. There was one 11/13 (0.846) result, and two 10/13 (0.769) results. No one scored below 6/13 (0.462).

The interesting thing is, that average proportion correct was 0.631, and it was significantly higher than chance (p=0.0322, Wilcoxon test; possibly unreliable t-test: p=0.0093). My interpretation is that the A/D/A process done with the Tascam recorder did audibly influence the signal.
No association of answers to any of the three questions with the proportion of correct answers was found.

Any comments?

[Juha]

By the specs, Tascam DV-RA1000 does not have very good A/D convertor(s) so, it would be nice to see RMAA results of it.

Juha