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## Re: Questions for audio gurus

 Subject: Re: Questions for audio gurus "Julius Thyssen" <> Thu, 23 Feb 2006 00:06:34 -0000
 ```Dan Seven wrote: > A quick question or 2 ..If a recorder is capable > of a frequency range of 20 to 20kHz such as a new > Tascam HD P2 and it can utilize192 kHz sampling > frequency, can you actually hear the upper end > of the audible range better? As the Whittaker=96Nyquist=96Kotelnikov=96Shannon sampling theorem states; When sampling a band-limited signal (e.g., converting from an analogue signal to digital), the sampling frequency must be greater than twice the input signal bandwidth in order to be able to reconstruct the original perfectly from the sampled version. The thing really important is the low-pass filtering that takes place when you sample audio. If you sample with 192 kHz, you'll be including sound up to 96 kHz. Say you have a microphone that picks up audio up to 18 kHz (and is REALLY not picking up ANY audio higher than 20 kHz). If you would sample that microphone output using a 44.1 kHz sample frequency, you will need to be sure that the band-pass filter works perfectly within 44.1 / 2 =3D 22.05 - 20 kHz =3D 2050 Hz. Most modern day analogue low pass filters on 16 bit samplers are almost perfect when they can use a transition band of 2000 Hz. So the 2050 Hz needed in this example is good enough. In this case you will not need a higher samplerate than 44.1 kHz. Some cheaper low-pass filters still touch lower frequencies more than they should. This is why people use oversampling, like with the use of 88.2 or 96 kHz. It is *only* required if the low-pass filters (used for the transition band of the needed anti-aliasing) are doing necessary work, because the audio that is being picked up has a higher freq. range than that which is sampled. This is only rarely the case. Personally I would never have signed the OK for Red Book CDDA (audio CD) standard. 22050 Hz is simply too close to the edge of our hearing range (asking for trouble and wasting the world's time with an imperfect format). 48 kHz samplerate would be a very good safe choice for most analogue recording and pick-up equipment out there. And to think people used to record from FM-stereo radio to cassette and were happy with the quality. ;-) We're talking *already* low-passed audio at 15 kHz. To equal that range, a sample rate of 32 kHz is sufficient. For some strange reason absurd frequencies have been made into a standard for DVD-audio. I think it's much more "because we can" than "because we need it". The thing causing this increase is that new equipment (and its analogue to digital converters and digital to analogue converters) has gotten better, resolution-wise. 24 bit is no problem anymore. That this would require a bigger frequency range for anti-aliasing, is, strange enough NOT true: The more can be done in the digital domain, the more perfect anti-aliasing will be. So the question is: How good is the anti-aliasing filter in your Tascam recorder ? There have been too many listening tests that proof beyond any doubt that humans do NOT hear the difference between originals and their 48 kHz or 96 kHz sampled recordings, simply because we can not feel or hear frequencies higher than 22 kHz, and the source of the sampled audio is rarely producing higher frequencies than 22 kHz at all. Plus, if it's only there to cause harmonics and timbre related influences, one could question its value; Most anti- aliasing artifacts are harmonically fine, they might cause a different sound than the original, but what will be left after masking by other louder parts in the spectrum is hardly measurable anyway. There's interesting reading (although already somewhat expired) on this subject here: http://www.promastering.com/pages/techtalk_mac/tt-3_mac.html -- Julius ________________________________________________________________________ ________________________________________________________________________ ```
 Current Thread Questions for audio gurus, Dan Seven Re: Questions for audio gurus, Rich Peet Re: Questions for audio gurus, Roger Norwood Re: Questions for audio gurus, Marc Myers Re: Questions for audio gurus, Julius Thyssen <= RE: Questions for audio gurus, Allen Cobb RE: Questions for audio gurus, Don Lloyd Re: Questions for audio gurus, Raimund Specht Re: Questions for audio gurus, Raimund Specht Re: Questions for audio gurus, Julius Thyssen Re: Questions for audio gurus, Rich Peet RE: Questions for audio gurus, Tom Duff RE: RE: Questions for audio gurus, Don Lloyd Re: Questions for audio gurus, Julius Thyssen Re: Questions for audio gurus, Julius Thyssen