Subject: RE: [linux-audio-dev] RFC: API for audio across network - inter-host audio routing
From: Bob Colwell (bob.colwell_AT_attbi.com)
Date: Sat Jun 15 2002 - 02:39:23 EEST
Nyquist says that if you sample a repeating waveform, ANY repeating
waveform, at a sampling rate greater than or equal to the highest
frequency partial present in the waveform, you can exactly duplicate
that waveform. Yes, exactly duplicate the original.
Lamar's comments are correct, but then, what difference is there
between amplitude modulation at the sampling frequency and a partial
at that frequency? Both contain information that cannot be captured
by the stated sampling frequency. Why would you amplitude modulate
anything that fast?
-BobC
-----Original Message-----
From: linux-audio-dev-admin_AT_music.columbia.edu
[mailto:linux-audio-dev-admin_AT_music.columbia.edu]On Behalf Of STEFFL,
ERIK *Internet* (SBCSI)
Sent: Friday, June 14, 2002 12:01 PM
To: 'linux-audio-dev_AT_music.columbia.edu'
Subject: RE: [linux-audio-dev] RFC: API for audio across network -
inter-host audio routing
> -----Original Message-----
> From: Lamar Owen [mailto:lamar.owen_AT_wgcr.org]
...
> The idea is that you get the integrated value of the
> amplitude of the sine
> wave, since a sine wave always has the same shape. But the
> amplitude, at the
> Nyquist frequency, cannot change. Yes, I really said that.
> If the amplitude
> of the sine wave changes, you get an upper sideband above the
> Nyquist rate
> that you cannot sample -- of course you also get a lower
> sideband that you
> can sample, but then the recovered envelope is distorted.
> Amplitude changes
> at the Nyquist frequency violate Nyquist's theorem. Thus the Nyquist
> frequency itself is an asymptote and cannot be accurately
> reproduced except
> in the steady state.
nyquist theorem doesn't say that you can get EXACT same signal if your
sampling frequency is twice the highest frequencey of signal. It says
(roughly) that you wouldn't miss any bumps (of frequency half of your
sampling frequency), you can't be sure about the shape of those bump
(amplitude).
which is basically what you say, it's just that there is no violation of
nyquist theorem there...
erik
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