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Audibility of a CD-Standard A/DA/A Loop Inserted into High-Resolution Audio Playback

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[Engineering Report] Claims both published and anecdotal are regularly made for audibly superior sound quality for two-channel audio encoded with longer word lengths and/or at higher sampling rates than the 16-bit/44.1-kHz CD standard. The authors report on a series of double-blind tests comparing the analog output of high-resolution players playing high-resolution recordings with the same signal passed through a 16-bit/44.1-kHz “bottleneck.” The tests were conducted for over a year using different systems and a variety of subjects. The systems included expensive professional monitors and one high-end system with electrostatic loudspeakers and expensive components and cables. The subjects included professional recording engineers, students in a university recording program, and dedicated audiophiles. The test results show that the CD-quality A/D/A loop was undetectable at normal-to-loud listening levels, by any of the subjects, on any of the playback systems. The noise of the CD-quality loop was audible only at very elevated levels.

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JAES Volume 55 Issue 9 pp. 775-779; September 2007
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Jonathan D. Boley
Comment posted August 27, 2008 @ 11:23:47 UTC (Comment permalink)

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.)


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Douglas Rife
Comment posted August 31, 2008 @ 00:40:34 UTC (Comment permalink)

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.


Drew Daniels
Drew Daniels
Comment posted September 14, 2008 @ 00:16:48 UTC (Comment permalink)

[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


Mark Jay
Mark Jay
Comment posted December 8, 2014 @ 18:09:58 UTC (Comment permalink)

I wholly applaud and agree with the reply posted by Drew Daniels. It is both eloquent and succinct; I also believe it to be in the proper spirit of the debate and solidly framed by reality. I would be remiss were I not to thank Messrs Meyer and Moran for having published this paper in the first place.

 
While I think there may be debate as to the 'precision' of the various approaches taken, the only thing of import is whether or not one method results in noticeably improved sound, and if said method can consistently be identified. If it cannot, then the rest is moot.
 
Again, Thank You Mr. (Dr.?) Daniels for your post.
 
Regards,
 
Mark A. Jay

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