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Old 02-25-2010   #110
Join Date: Dec 2008
Location: Varennes, Québec
Posts: 41
Default Re: High end processors VS low end processors/receivers, hardware differences?

Here's something interesting and it even might be educating for some:

Robert Harley -- Wed, 05/28/2008 - 15:18

The following is my editorial from The Absolute Sound Issue 183 (not yet published) on blind listening tests.

The Blind (Mis-) Leading the Blind

Every few years, the results of some blind listening test are announced that purportedly “prove” an absurd conclusion. These tests, ironically, say more about the flaws inherent in blind listening tests than about the phenomena in question.

The latest in this long history is a double-blind test that, the authors conclude, demonstrates that 44.1kHz/16-bit digital audio is indistinguishable from high-resolution digital. Note the word “indistinguishable.” The authors aren’t saying that high-res digital might sound a little different from Red Book CD but is no better. Or that high-res digital is only slightly better and not worth the additional cost. Rather, they reached the rather startling conclusion that CD-quality audio sounds exactly the same as 96kHz/24-bit PCM and DSD, the encoding scheme used in SACD. That is, under double-blind test conditions, 60 expert listeners over 554 trials couldn’t hear any differences between CD, SACD, and 96/24. The study was published in the September, 2007 Journal of the Audio Engineering Society.

I contend that such tests are an indictment of blind listening tests in general because of the patently absurd conclusions to which they lead. A notable example is the blind listening test conducted by Stereo Review that concluded that a pair of Mark Levinson monoblocks, an output-transformerless tubed amplifier, and a $220 Pioneer receiver were all sonically identical. (“Do All Amplifiers Sound the Same?” published in the January, 1987 issue.)

Most such tests, including this new CD vs. high-res comparison, are performed not by disinterested experimenters on a quest for the truth but by partisan hacks on a mission to discredit audiophiles. But blind listening tests lead to the wrong conclusions even when the experimenters’ motives are pure. A good example is the listening tests conducted by Swedish Radio (analogous to the BBC) to decide whether one of the low-bit-rate codecs under consideration by the European Broadcast Union was good enough to replace FM broadcasting in Europe.

Swedish Radio developed an elaborate listening methodology called “double-blind, triple-stimulus, hidden-reference.” A “subject” (listener) would hear three “objects” (musical presentations); presentation A was always the unprocessed signal, with the listener required to identify if presentation B or C had been processed through the codec.

The test involved 60 “expert” listeners spanning 20,000 evaluations over a period of two years. Swedish Radio announced in 1991 that it had narrowed the field to two codecs, and that “both codecs have now reached a level of performance where they fulfill the EBU requirements for a distribution codec.” In other words, Swedish Radio said the codec was good enough to replace analog FM broadcasts in Europe. This decision was based on data gathered during the 20,000 “double-blind, triple-stimulus, hidden-reference” listening trials. (The listening-test methodology and statistical analysis are documented in detail in “Subjective Assessments on Low Bit-Rate Audio Codecs,” by C. Grewin and T. Rydén, published in the proceedings of the 10th International Audio Engineering Society Conference, “Images of Audio.”)

After announcing its decision, Swedish Radio sent a tape of music processed by the selected codec to the late Bart Locanthi, an acknowledged expert in digital audio and chairman of an ad hoc committee formed to independently evaluate low-bit rate codecs. Using the same non-blind observational-listening techniques that audiophiles routinely use to evaluate sound quality, Locanthi instantly identified an artifact of the codec. After Locanthi informed Swedish Radio of the artifact (an idle tone at 1.5kHz), listeners at Swedish Radio also instantly heard the distortion. (Locanthi’s account of the episode is documented in an audio recording played at workshop on low-bit-rate codecs at the 91st AES convention.)

How is it possible that a single listener, using non-blind observational listening techniques, was able to discover—in less than ten minutes—a distortion that escaped the scrutiny of 60 expert listeners, 20,000 trials conducted over a two-year period, and elaborate “double-blind, triple-stimulus, hidden-reference” methodology, and sophisticated statistical analysis?

The answer is that blind listening tests fundamentally distort the listening process and are worthless in determining the audibility of a certain phenomenon.

As exemplified by yet another reader letter published in this issue, many people naively assume that blind listening tests are somehow more rigorous and honest than the “single-presentation” observational listening protocols practiced in product reviewing. There’s a common misperception that the undeniable value of blind studies of new drugs, for example, automatically confers utility on blind listening tests.

I’ve thought quite a bit about this subject, and written what I hope is a fairly reasoned and in-depth analysis of why blind listening tests are flawed. This analysis is part of a larger statement on critical listening and the conflict between audio “subjectivists” and “objectivists,” which I presented in a paper to the Audio Engineering Society entitled “The Role of Critical Listening in Evaluating Audio Equipment Quality.” You can read the entire paper here I invite readers to comment on the paper, and discuss blind listening tests, on a special new Forum on The Forum, called “Evaluation, Testing, Measurement, and Perception,” will explore how to evaluate products, how to report on that evaluation, and link that evaluation to real experience/value. I look forward to hearing your opinions and ideas.

Robert Harley
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