AES Journal Forum

My compliments to the authors for performing this study. The result that immediately struck me as odd was the fact that female subjects scored 37.5% correct... well below chance. I wonder, was the variability greater for this subject pool?
Also, were the results analyzed only in terms of correct/incorrect? Or were the results also analyzed for false positives and false negatives?
For example, it would be interesting if the female subjects, or anyone else, tended to be biased toward answering either A or B, thus skewing the results. (This would be a great opportunity to apply Signal Detection Theory.)

I read this paper with great interest when first published almost 1 year ago. Considering recent efforts promoting the supposed superiority of high resolution digital audio formats (24 bit, 96 kHz PCM as well as DSD) the authors' conclusion of no detectable audio quality difference between these formats compared to ordinary CD resolution (16 bit, 44.1 kHz PCM) would indeed be expected to create controversy. While I'm sympathetic to the authors' findings, it would have been a much stronger paper if the authors had revealed exactly what "well regarded CD recorder with real-time monitoring" was used to reduce the resolution of the audio signal to the CD standard. The authors claim their mystery CD recorder performed an A/D conversion using only 16-bit resolution and a 44.1 kHz sampling rate, followed by an immediate conversion back to the analog domain using a 16-bit, 44.1 kHz DAC (see Figure 1). But readers have no way to verify this claim without knowing the exact equipment the authors used in their tests and that they verified by correspondence with the manufacturer of this mystery CD recorder that the A/D/A conversion block shown in Figure 1 of their paper was actually being implemented. In other words, the authors need to leave no doubt that this block is really an A/D/A function at 16-bit resolution and not, for example, a purely analog monitor function or, one made at a higher bit resolution or sample rate.

[Recently an article on audio quality by Meyer and Moran (J. Audio Eng. Soc. vol. 55, pp. 775-779, [2007 Sep.]) has given rise to a number of letters sent to the Journal. There is a lot of intense debate and opinion on this topic that probably would be interesting to many AES members, and this might actually help to bring out the key aspects of the issue. Accordingly, we feel that an AES online forum that allows members to give their opinions and experiences will be valuable.]—JAES e-mail to members.

That debate about this issue is intense there is no doubt. Can such debate be borne entirely of electroacoustical differences which might actually be impossible to explain, demonstrate and reproduce in a statistically significant way, or is it perhaps possible that financial interests could be at risk if some ultimate determination of audibility suggested that a large number of digital audio products were overbuilt, overpriced, or even entirely unnecessary?

This author deplores fear-mongering and considers its use as a marketing tool on people with insecurities about their technical knowledge, a crime of fraud. The audio marketplace, its many commercially oriented magazines, and the manufacturers who advertise in these magazines, now rarely if ever, supply graphical engineering data or even detailed and accurate print information that might be used to make purchasing decisions. The vast majority of equipment manuals are a list of sales points and usually not helpful. More and more, manufacturers rely on convincing potential customers of the superiority of their products by subjective means and anecdotal comments from celebrities. This is marketeering—not engineering--and it harms consumers everywhere. Those who are forced to purchase manufactured products to remain competitive in their services to clients, products which can not be tested in personal labs before purchases are made, should speak up about what has become an excessively greedy and cynical marketplace where increasingly, we are victims of marketeers rather than beneficiaries of good engineering.

Drew Daniels

I also applaude the initiative, although I also agree with Douglas Rife's arguments. I personally don't believe that the extended frequency respons offered by higher sample rates is of any consequence. Many people that claim to hear differences (including myself), are at an age where even 15 kHz might be of little interest. And let's not forget that 10kHz to 20 kHz is only one of the ten octaves of the DIN 45.500 hifi standard (20 to 20,000Hz). Let's look beyond the obvious. Some listeners might be wrong in claiming they can hear the difference between 44.1/16 and 192/24, but can they all be wrong?

I have experienced a comparable judgement when in the eighties I claimed to hear differences between two S/PDIF cables between a CD-player and DAC. I was put down like now is done with those who claim to hear higher fs. It was even 'proven' that I was wrong: a file was copied via two different S/PDIF cables and then compared at bit level on a Sonic Solutions system. Both files were identical, so I was wrong. We now know that incorrect digital cables cause jitter that can be corrected by buffering (storing in the case of the Sonic system) but can't be corrected when feeding a DAC.

Regarding the high sample rates: research done by Bob Stuart and Peter Craven might go in the right direction. They found literature that indicate our auditory system has a time resolution  of 7 µs, which would need a sample rate of 141 kHz or better. They also work on a codec that reduces the time smearing (caused by anti-aliasing and reconstruction filters) in the total record-reproduce chain. Both seem credible to me and would make the research on whether we directly or indirectly) hear content above 20 kHz less relevant.

Regardless the above I thank the researchers and members of the BAC for persuiing the thruth by putting large amounts of time in this project.   

Do you know of efforts to replicate this result while using contemporary high-resolution sources, and also moninors with upper bandwidth limit around 40 KHz (e.g. Adam, Focal) ? To the best of my knowledge, such monitors only started to appear around 2010.

In my personal experience, I only started noticing significant advantages of SACD when I switched to Adam. To me, it mostly manifests itself as a strong "presense effect", especially on classical recordings. I've never experienced it to such degree with any CD recordings.

It is not about the frequency range, naturally - can't hear much above 13 KHz - but about the perception of simultaneous presense of non-interfering sound sources of wildly differing intensities in different spacial locations, including more realistic delayed reflections. I can see - mathematically - how longer words and higher rates may contribute to that.