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In Reply to: Re: The Nyquist/Shannon theorum is one of the most mis-quoted and misunderstood concepts in audio! posted by JRB on April 15, 2001 at 23:08:05:
I agree with all your points, and I think you agree with mine. Our emphasis is different. My emphasis is on the fact that trying to reconstruct aperiodic signals varying many tens of dB wihin a couple of cycles of a Nyquist-specified period with four samples doesn't work. I agree, for example, that if you know, at the outset, that you are dealing with monochromatic sine waves, you can sort it all out fairly quickly (by looking at the beat frequency) if the samples are at slightly greater than twice the frequency of the signal. But in that case, you had very little to sort out to begin with. Its like saying that all you need to know about amplifiers is total harmonic distortion, which is also based on monochromatic sine waves. (I know that is not what you are saying; what you said was correct, and well put.) If you are dealing with cymbal clashes (that create nasty little pulses that look like hair on an oscilloscope trace and are about as aperiodic as it gets) or even violins, which have very little in common with sine waves, you can't get it done anywhere near the Nyquist limit with a simple roll-off filter. Yet every day, some genius with a BS in EE (who has forgotten how to integrate dx from zero to unity) with spout off that "if *you* would just remember Nyquist or Shannon, you'd know that all the information is there for the taking, right up to 22.05 Khz." It took about 15 years to beat the THD idea out of that class of engineering genius, and a few of them still proclaim THD as the only needed MOM every now and then!Sorry, I'm tired and irritable. I'm sure they're really nice people, who, most of the time are neither arrogant nor condescending to the great unwashed masses that the seek to "educate."
I agree that the guys who do this every day may have a grip, but I wouldn't bet the farm on it. I work with the biggest name aerospace firms in the world, and I'm constantly amazed at the lack of grip that I find, so why should all of the grip-holders have ended up in audio? (Long day.)
I also agree that there is no "magic" in this business, and I find it particularly tiring when people claim that there is. (It's particularly off-putting when they proclaim it with a lecturing tone.) If it were magic, we'd either develop our equipment by casting spells or by pure trial and error. In reality, we do our designs based on the best that we understand about engineering, and then do some trial-and-error "voicing" at the end to tweak-in some fine tuning. We might trade off some macro design options based on sonics, but we do understand the principles of those designs, even if we're not absolutely sure why one sounds better than another. That's about all the "magic" we can practically inject into the process. (Yes, I've dabbled in audio electronics design myself, so I appreciate the process. While I don't claim to be an industry-experienced expert, I can recognize BS fairly consistently.)
I wish you, JRB, would go to the MSB website and record your reaction to what they are saying. BTW, I have an MSB product that I'm very happy with, so I certainly tend to cut them slack. I just find all this differentiation between interpolation, oversampling, and upsampling to be puzzling.
Tim
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- Re: The Nyquist/Shannon theorum is one of the most mis-quoted and misunderstood concepts in audio! - TimNaff 23:37:55 04/16/01 (0)
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