A | B | X when A = B

Yesterday, I focused on the fallacy that 16-bits of dynamic range is sufficient to capture and release all music. It is true that the vast majority of commercial music releases (in any format including vinyl LPs, analog tape, compact disc, SA-CD and DVD-Audio) don’t exceed this limit on dynamic range. However, my point was that some do and therefore we should demand that our standards for delivery move to the 24-bit standard of high definition recording. The move to 24-bits will ensure that the dynamic range of real life CAN be delivered to consumers that want it. Why accept less?

The same xiph.org article mentioned the “rigorous” tests that were performed by a couple members of the Boston Audio Society back in 2007. E. Brad Meyer and David R. Moran co-wrote an article was called, “Audibility of a CD-Standard A/D/A Loop Inserted into High-Resolution Audio Playback”. The basic premise of the piece is that “high-resolution” formats like SA-CD and DVD-Audio (and now high-resolution downloadable files) cannot be distinguished from standard definition CDs. Their extensive tests sent the outputs from SA-CD and DVD-Audio players straight into an A |B | X switcher AND into a box that did a real time conversion from “high-resolution” to Redbook standard (44.1 kHz/16-bits). The output of the switcher would contain either the original “high-resolution” source OR the same material down converted to CD resolution. None of the equipment or cables they used were high-end by today’s standards.

Figure 1 – Setup of the Boston Audio Society A | B | X test rig for evaluating “high-resolution” content vs. standard CDs.

Their conclusion was that no one was able to tell the difference. They stated, “The test results for the detectability of the 16/44.1 loop on SACD/DVD-A playback were the same as chance: 49.82%. There were 554 trials and 276 correct answers.”

The article caused a great deal of controversy at the time and it still is quoted (as in the piece at xiph.org) as proof that high-resolution audio is completely unnecessary. We should all be content with the “perfect” sound of compact discs.

However, Brad and David missed the most important component of the entire test setup…the sources. How can you test for something that isn’t in any of the samples? At the time of the paper, I corresponded with David and asked about the source material that their members brought with them for the evaluations. The original article didn’t mention which SA-CDs and DVD-Audio discs were included in the testing. I was very heartened to learn that the list didn’t include any AIX Records releases (at the time we were doing on DVD-Audio using 96/24 PCM).

The partial list of tested albums was released some time after the original paper. The list included:

Patricia Barber – Nightclub (Mobile Fidelity UDSACD 2004)
Chesky: Various — An Introduction to SACD (SACD204)
Chesky: Various — Super Audio Collection & Professional Test Disc (CHDVD 171)
Stephen Hartke: Tituli/Cathedral in the Thrashing Rain; Hilliard Ensemble/Crockett (ECM New Series 1861, cat. no. 476 1155, SACD)
Bach Concertos: Perahia et al; Sony SACD
Mozart Piano Concertos: Perahia, Sony SACD
Kimber Kable: Purity, an Inspirational Collection SACD T Minus 5 Vocal Band, no cat. #
Tony Overwater: Op SACD (Turtle Records TRSA 0008)
McCoy Tyner Illuminati SACD (Telarc 63599)
Pink Floyd, Dark Side of the Moon SACD (Capitol/EMI 82136)
Steely Dan, Gaucho, Geffen SACD
Alan Parsons, I, Robot DVD-A (Chesky CHDD 2003)
BSO, Saint-Saens, Organ Symphony SACD (RCA 82876-61387-2 RE1)
Carlos Heredia, Gypsy Flamenco SACD (Chesky SACD266)
Shakespeare in Song, Phoenix Bach Choir, Bruffy, SACD (Chandos CHSA 5031)
Livingston Taylor, Ink SACD (Chesky SACD253)
The Persuasions, The Persuasions Sing the Beatles, SACD (Chesky SACD244)
Steely Dan, Two Against Nature, DVD-A (24,96) Giant Records 9 24719-9
McCoy Tyner with Stanley Clark and Al Foster, Telarc SACD 3488

So here’s the problem…16 out of the 19 listed above are SA-CDs. And as has been pointed out on this site and others, the amount of noise in frequency range higher than 20 kHz on any disc made with DSD 64 requires a LPF (Low Pass Filter) be applied to get rid of it. So in fact, none of the SA-CD discs should have sounded any different than the sources that they were made from. The whole idea of SA-CD and DSD at the time was to improve on compact discs…not to establish the world of high-resolution audio. DVD-Audio and PCM didn’t limit the ultrasonics. If the music contained 45 kHz partials, then the DVD-Audio discs played them back. Not so for SA-CD.

Two of the DVD-Audio discs on the list were originally recorded on analog tape. Analog tape has very limited dynamic range and compromised ultrasonics. Once again, the results were assured from the outset of the test…if the sources didn’t have anything requiring 24-bits of dynamic range or extended frequency response, then why would anyone think that the DVD-Audio would? Switching between things that are essentially identical would nullify the results.

I can’t say for certain that my recordings would have produced different results, but there would at least be a fighting chance that they would. I record projects without any dynamics compression or mastering. I use high definition PCM at 96 kHz/24-bits, which does capture ultrasonics and deliver them during playback. With a critical system and the right listening environment, the results might have been different.

If you design and execute a poor test then the results are meaningless. The article and xiph.org’s reference to it only contribute to the misinformation about HD-Audio.

I strongly believe that we should expand the standards of audio recording to HD standards using high sample rate and longer word length PCM. Then, and only then, will engineers and producers know that the delivery formats will deliver their music in the way they envisioned it.