Golden Earring wrote: > Morning Arny! > > I wondered if you had any direct comments on the research paper that I > referenced (which may or may not prove to be good science depending on > whether the claimed results are confirmed independently). The test > results were intriguing if valid. >
On the plus side Bill Waslo is one of the good guys and knows audio technology reasonably well. On the minus, I see the need, but also am highly critical of the analysis of difference signals. If you are dealing with irrational audiophiles, then tools like the Diffmaker make some sense because at the very lowest levels, difference-taking can be used to enhance the sensitivity of *REAL* audio analysis hardware and software which is typically FFT-based. *The problem with differences is that they are inherently non-discriminatory.* The real-world situation is that signals where the errors are reliably perceptible by humans, everything is clear and readily measurable. Remember, the threshold of audibility for all audible artifacts is on the order of 60 or 70 _or_less__ dB down if you get your gains set right. At those levels one can measure things to the point of exhaustion with low cost readily available gear and software. Any artifact that is say 100 or less dB down is not that hard or expensive to analyze to death. A lot of people don't know this but almost all modern audio test gear first digitizes the signal, often with an off-the-shelf analog-to-digital converter. Almost all modern pro audio signal processing gear with analog inputs works in a similar fashion, converting the signal to the digital domain, and then using processing in the digital domain to obtain the desired audible effects. Currently, pro audio gear costing $200 and up can be front ended by an ADC that has about -113 dB artifacts of its own. For testing purposes, you don't need anything better. So the question becomes do we need any better measurements than these to do technical tests with. In almost every case in the rational world the answer is *no*. So then, differencing becomes a solution that is looking for a problem because all of the realistic problems are already solved by other, highly conventional means that give more precise and more detailed answers. With differencing and other add-ons, measurements in the -140 to 160 dB range are possible. In this range, even ordinary copper wire and resistors have measureable distortion. But pinch yourself, we are talking twice the normal regular threshold of hearing *on a logarithmic scale*. Fun, but mostly to impress people who don't know any better. Correct me if I'm wrong here but I believe Shannon's sampling theory proof based on Nyquist's earlier conjecture (which only concerned Morse code, a digital source) if the sampling frequency is not completely regular is dependent upon the noise components mixed with the signal being "i.i.d." (independent & identically distributed) & that if that is *-not-* the case there may be theoretical problems in the interpolation process necessary for the reconstruction of the original analogue signal (I think that the Cheung-Marks Theorem covers an extreme aspect of this, where they show the addition of an arbitrarily small amount of *-non--*i.i.d. noise, such as that arising from quantisation errors, may make the reconstruction process "ill-posed" which is maths jargon for saying it no longer has a unique solution), IOW -the precise job that the DAC is attempting-, and in particular that suggestions made by Shannon in attempting to generalise his results to irregular sampling intervals are not correct. Even small instabilities might have some effect following this line of thought. This is all rather heavy stuff, & I'm guessing that any audible differences would tend to arise in the quiet passages of source material with a high dynamic range where the difference between the signal amplitude & the noise floor is reduced. Just perhaps some people may be attuned to "digital jitter" in this wider sense of including clock drifting inaccuracies, in an analogous way to the fact that you found early CD's (which did have some problems of their own in terms of engineering quality of recording) preferable to analogue, whereas at that stage I definitely preferred my (mature technology) analogue set-up. It's just a thought. Obviously we don't capture the full concert hall dynamic range of an orchestra even with our digital recordings, & if we did either the quiet parts would be smothered by ambient noise or the loud parts would make our ears bleed in the context of domestic listening. It's a question of producing a subjectively satisfying illusion of the underlying musical performance ultimately which may leave -some- "wriggle-room" for individual preferences yet. Still staying open minded atm this side of the pond. Dave :) ------------------------------------------------------------------------ arnyk's Profile: http://forums.slimdevices.com/member.php?userid=64365 View this thread: http://forums.slimdevices.com/showthread.php?t=106519 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/mailman/listinfo/audiophiles
