There is small but noticeable buzz circulating among audiophile sites, FB pages of prominent audio experts, and even mainstream websites stating without reservation that high-resolution audio has been proved to be perceptible. I’ve read no fewer than 6 headlines pronouncing things like, “Hi-Res Passes Key Test” (CEOUTLOOK.COM), “It’s Official: People Can Hear High-Res” (Audiostream), and “HD audio is perceptibley [sic] better than CDs”. Robert Stuart, the man behind MQA and a staunch supporter of high-resolution audio posted “This is a landmark day for audio”, on his FB page yesterday.
These posts and articles spring from a peer reviewed AES (Audio Engineering Society) paper by Dr. Josh Reiss of Queen Mary University of London titled, “A Meta-Analysis of High Resolution Audio Perceptual Evaluation”. He wrote to a number of parties — including me — yesterday with the article attached. Dr. Reiss didn’t do a study to arrive at his conclusion that his study found “high resolution audio has a small but important advantage in its quality of reproduction over standard audio content”. He did a meta study of previous high-resolution audio studies. Here’s the abstract from his paper.
“There is considerable debate over the benefits of recording and rendering high resolution audio, i.e., systems and formats that are capable of rendering beyond CD quality audio. We undertook a systematic review and meta-analysis to assess the ability of test subjects to perceive a difference between high resolution and standard, 16 bit, 44.1 or 48 kHz audio. All 18 published experiments for which sufficient data could be obtained were included, providing a meta-analysis involving over 400 participants in over 12,500 trials. Results showed a small but statistically significant ability of test subjects to discriminate high resolution content, and this effect increased dramatically when test subjects received extensive training. This result was verified by a sensitivity analysis exploring different choices for the chosen studies and different analysis approaches. Potential biases in studies, effect of test methodology, experimental design, and choice of stimuli were also investigated. The overall conclusion is that the perceived fidelity of an audio recording and playback chain can be affected by operating beyond conventional levels.”
As a strong advocate for high-resolution audio/music, I’m encouraged by his meta analysis of the existing literature (at least the 18 studies that he included in the paper…including the infamous Meyer and Moran AES paper). But as we all know, the devil is in the details. I found the paper lacking for a number of reasons…starting with the definition of high-resolution audio.
The opening sentence gets straight to the most important issue associated with high-resolution audio/music. The paper states, “High resolution audio may be loosely defined as those systems and formats that are capable of rendering beyond standard quality audio, i.e., more than 16 bits, and/or more than 44.1 or 48 kHz sample rate, as used in Compact Disc (CD) or ‘ordinary’ Digital Video Disc (DVD) quality audio.”
Reading carefully, Dr. Reiss establishes “standard quality audio” as PCM digital audio with specifications of more than 48/44.1 kHz sampling rates and 16-bits. Already, we have a disconnect. The CTA/CEA Audio Board, major record labels, DEG, and NARAS organizations don’t endorse this definition. I fought long and hard to get the CEA board to move their definition above CD specifications as the baseline for high-resolution audio. The result was I got kicked off the board. Dr. Reiss’ definition does nothing to help solidify the “looseness”. I would suspect that a paper of this magnitude would have to have a rigorous definition in order to report any valid results. Did the studies that he examined use 48 kHz/20-bit PCM audio or something higher? 48/20 is high-resolution audio in the minds of the previously mentioned organizations.
One of my biggest complaints is the focus on the “rendering” or delivery side of the audio production chain. This completely ignores the “provenance” of the recording itself. This is the trap that Meyer and Moran fell into and is what makes their AES paper so utterly useless (but it has been used by those opposing HRA for almost ten years!). The content — the recordings used in any of the studies — has to actually contain ultrasonic frequencies and possess dynamic range higher than a standard CD. Although the paper specifically states that it didn’t analyze the papers for perceptible differences associated with greater bit depths, I believe the move to greater dynamics is more likely to be perceptible than ultrasonic frequencies.
I am familiar with many of the 18 studies that Dr. Reiss analyzed and know that with the exception of the Meyer and Moran paper, most of the recordings used were not commercial high-resolution audio recordings. Some of the best studies made their own recordings using high-resolution equipment and took great care to ensure that ultrasonic frequencies were present. It was necessary to make new recordings because there aren’t very many commercially available.
The paper acknowledges that “jazz and classical” music was generally used…not rock, folk, pop, or country music. Dr. Reiss said, “The studies that most showed an effect mainly used jazz and classical music, but this wasn’t exclusive”. So we have another disconnect. The headlines are cheering in support of the paper and “proof” of high-resolution audio’s perceptibility for a very narrow category of music while the industry (both hardware and software) continues to promote and sell recordings that no one would be able to distinguish from their standard-resolution CD versions and a high-resolution transfer into 96 kHz/24-bits.
Sometimes it’s the stuff that isn’t featured that is the stuff that matters most. The provenance of the “chosen stimuli” (the recordings that were actually played for the subjects) is the most important thing…and it doesn’t get much play in the AES paper.
I applaud Dr. Reiss for his important work. He rightly describes the kinds of things that need to done during another study into the merits of high-resolution audio. I would love to be involved in a rigorous study, but the media and many supporters have already proclaimed the myth of high-res audio, as it currently exists, as fact.
You can download the paper from the AES Journal site: Journal of the AES.