Hi Rich,
yes, you're right. Even if you don't need to record
frequencies above 20 kHz, if your source is rich of ultrasonic
frequencies around the Nyquist frequency you may incur in some
artifacts at the edge of audible range. You can avoid them by moving
the Nyquist frequency well beyond the range of frequencies you
capture. In this case you can add some soft low-pass filtering in the
analog domain (maybe the mic frequency response is enough...), but as
you are not interested in the ultrasonic range at all, you can also
also do digital filtering before downsampling back to your desired rate.
Gianni
At 19.48 27/02/2006, you wrote:
>Thank you.
>What I read into this as a lay person is that the filters are not
>strong enough. And so, when I record a sound that includes a lot of
>high freq content (bug season during August, here) I need to record at
>24/96 just to have the ability of doing a low pass filter first before
>the anti-ali filter because the filters do not support the full range
>of the audio supported by the resolution at 24 bit.
>
>What I am changing in my recording style is to record at 24/96 and
>then do a low pass separate and before the anti-ali filter. This
>appears to be needed to be done before converting back to human
>audible 44.1. Note this is for me because what I produce will only be
>heard by man and I want that part to be accurate.
>
>I hope this makes sense and follows the result of your graphs.
>Rich
>
>--- In Gianni Pavan <> wrote:
> >
> > Hi all,
> > as promised I set up a webpage with the results of the measures I do
> > on the equipment I use in the lab.
> > I hope you'll find them interesting. All your comments are welcome.
> >
> > http://www.unipv.it/cibra/res_techtest_uk.html
> >
> > Gianni
> >
>
>
>
>
>
>"Microphones are not ears,
>Loudspeakers are not birds,
>A listening room is not nature."
>Klas Strandberg
>Yahoo! Groups Links
>
>
>
>
>
>
>
>
>
>
>--
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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 +39-0382-987874
Fax +39-02-700-32921
Web http://www.unipv.it/cibra
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