The high-resolution audio world was just getting started when a couple of students at the Tonmeisterinstitut, University of Music Detmold, Germany decided they would do a rigorous study on the sonic differences (if any) between the two physical formats that were available to audiophiles. This was in 2004. The title of their AES paper is “DVD-Audio versus SACD / Perceptual Discrimination of Digital Audio Coding Formats / Listening Comparison Test between DSD and High Resolution PCM (24-bit / 176.4 kHz)” and it was authored by Dominick Blech and Min-Chi Yang. I admit I hadn’t read it previously but I was impressed with the rigor of the study and the scholarship of the resulting study. It brings into question the very essence of the DSD vs. PCM debate. Here’s the abstract:
“To study perceptual discrimination between two digital audio coding formats, ‘Direct Stream Digital’ and high-resolution (24-bit, 176.4 kHz) PCM, subjective listening comparison tests were conducted with specially recorded sound stimuli in stereo and surround.
To guarantee their reliability, validity and objectivity, the double-blind ABX tests followed three main principles: The signal chain should be based on identical audio components as far as possible; these components should be able to convey very high audio frequencies; and the test population should consist of various groups of subjects with different listening expectations and perspectives.
The results showed that hardly any of the subjects could make a reproducible distinction between the two encoding systems. Hence it may be concluded that no significant differences are audible.”
They used ABX testing between a series of new recordings that they produced themselves in both DSD 64 and PCM at 176.4/24-bits. The entire signal chain between the DSD and PCM recordings was very carefully matched with regards to timing, level, processing (none was done to either signal), and reproduction with the exception of the analog to digital and digital to analog conversion. Obviously, in a test of this type the converters must be different. However, in this case they used a dCS 904 converter, which allows conversion in both formats by the same manufacturer. You can read the paper for yourself but they authors took great care to use the very best microphones, cabling, electronics, speakers. They signal path would quality for the JAS definition of high-resolution…which enhances the frequency response to 40 kHz.
The recordings were done with minimal microphone technique. New stereo and surround recordings were made with Schoeps MK 2s, MK4 and MK 41 capsules (with a frequency response to 50 kHz).
The listening/evaluation period took place over 28 days and resulted in 145 tests taken by 110 participants. There were 43 women and 67 men ranging in age from about 20 to over 75. The mean age of 32.9. The pool of listeners included professional recording engineer, music students, professional musicians, a piano tuner, music reviewer, and other non-music professions.
Here’s the summary of the research project:
“These listening tests indicate that as a rule, no significant differences could be heard between DSD and high-resolution PCM (24-bit / 176.4 kHz) even with the best equipment, under optimal listening conditions, and with test subjects who had varied listening experience and various ways of focusing on what they hear. Consequently it could be proposed that neither of these systems has a scientific basis for claiming audible superiority over the other. This reality should put a halt to the disputation being carried on by the various PR departments concerned.”
You can take what you will from this study. It was done over 14 years ago and many things have changed…improved…over that span of years, but the essential premise of this study has remained the same. When audiophiles, equipment manufacturers, reviewers, and publications say that they can tell the difference between DSD 64 and high-resolution PCM recordings, chances are it’s not the format that they’re hearing but the nature of the production process associated with each version.
Perhaps there is no sonic difference between DSD (at any multiple) and high-resolution PCM. If that’s true, then I believe that PCM deserves the spotlight because it doesn’t suffer from the lack of tools, the ultrasonic noise, and file size inflation. It might be time to relegate DSD to “also ran” status and get back to making better sounding records.