At 18.01 19/10/2005, you wrote:
>Can you describe what you mean by this file? How do you make it? Sorry
>if it is a dumb question...
>
><L>
I create a 16 bit stereo .wav file and I fill it
with integer samples with values
-32000,+32000,-32000,+32000 ... with a program
written in Visual Basic. Such a sequence of
samples corresponds to a perfect sinusoid at the
Nyquist frequency (half of the sampling rate)
that can't be recorded from an analog source.
If you feed a non-resampling digital input the
values are just kept and stored in a new file.
But if the digital input device resamples the
data stream all those value are processed with a
resampling algorithm that produces a new series
of samples that don't match with the original
ones. A resampler keeps the original stream,
upsamples to a much higher frequency, performs a
digital filtering to cut frequencies higher than
the new sampling rate (that could be the same of
the input or a different one) and also attenuates
frequencies close to the Nyquist frequency, then
downsamples to the final rate. If your original
stream is 48k and the output of the resampler is
exactly 48k again, frequencies higher than
22-23kHz will be attenuated and the "Nyquist
signal" will be greatly attenuated.
In some cases the input stream has not exactly
the rate of the sound board clock and in this
case the "Nyquist signal" will appear at a
frequency that is not the Nyquist frequency of the new file.
A "no resampling" digital input is able to lock
on the incoming rate and to transfer samples
without any further processing. If you open with
Audition the file created by the digital input
device you see very clearly the difference among
resampled and not-resampled "Nyquist signal"
I hope I was clear enough,
Gianni
>Lou Judson =95 Intuitive Audio
>415-883-2689
>
>On Oct 19, 2005, at 12:37 AM, Gianni Pavan wrote:
>
> > Create an "impossible" file with samples alternating among -max and
> > +max (-32700,+32700,-32700,+32700,....)
> > Play the file through a digital output
--------------------------------------------------------------
Gianni Pavan
Email
Centro Interdisciplinare di Bioacustica e Ricerche Ambientali
Universita' degli Studi di Pavia
Via Taramelli 24, 27100 PAVIA, ITALIA
Tel +39-0382-987874
Fax +39-02-700-32921
Web http://www.unipv.it/cibra
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