I definitively confirm that the UA5, which is impressive on analog inputs,
does resampling on digital inputs.
By using a true digital I/O card (I'm using the excellent SEKD 96PRO) it is
easy to check: create a .wav file with a sine-wave at exactly the Nyquist
frequency of the device you want to test (I did it with CoolEdit Pro). Play
the file on the digital output of the board you're sure it doesnot resample
(the SEKD in my case) and record - on the same PC - with the board (the UA5
in my case) you want to test. Also, by using two concurrent sessions of
CoolEdit you can record the reference digital signal by using the digital
inputs of the same board you use for playing it.
The signal recorded with the SEKD board (outputs directly connected to
inputs) is identical to the reference signal, while the signal recorded
through a resampling digital input may be very different: with the UA5 I
got a signal of lower amplitude because of the attenuation digital filters
have close to Nyquist and amplitude modulated because of the small
difference among the reference sampling rate (exactly 96000) and the
resampling rate of the UA5 which is slightly different (few Hertz). The
difference among the two rates produces beats in the resampled signal when
the signal frequency is close to Nyquist.
I hope this method could help in determining which audio devices resample
digital inputs and which not.
Gianni
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Gianni Pavan
Email
Centro Interdisciplinare di Bioacustica e Ricerche Ambientali
Universita' degli Studi di Pavia
Via Taramelli 24, 27100 PAVIA, ITALIA
Tel/Fax +39-0382-525234 Laboratori
Tel/Fax +39-0382-526208 Segreteria
Web http://www.unipv.it/cibra
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