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Date:      Mon, 22 Dec 1997 17:41:25 +0100 (MET)
From:      Luigi Rizzo <luigi@labinfo.iet.unipi.it>
To:        hasty@rah.star-gate.com (Amancio Hasty)
Cc:        steve@visint.co.uk, multimedia@freebsd.org
Subject:   Re: precise soundcard tuning ?
Message-ID:  <199712221641.RAA02728@labinfo.iet.unipi.it>
In-Reply-To: <199712221733.JAA01209@rah.star-gate.com> from "Amancio Hasty" at Dec 22, 97 09:33:31 am

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> The sound blaster cards are known not to be very precise sound cards.

the data sheets of the OPTi931 also show the deviation between nominal
and actual sample rate and it turns out to be within 0.1% in many
cases. Not big deal but it is noticeable.

While i was developing a delay compensation mechanism for my
telephone app, I was printing the difference between the expected
arrival time of data packets (based on the RTP timestamp which in
turn is based on the card sample clock) and the actual arrival time
(computed using the cpu clock).

It took some minutes to realize that the drift of about 8 samples/s
was not a bug in my code but rather the clock drift!

	Cheers
	Luigi
-----------------------------+--------------------------------------
Luigi Rizzo                  |  Dip. di Ingegneria dell'Informazione
email: luigi@iet.unipi.it    |  Universita' di Pisa
tel: +39-50-568533           |  via Diotisalvi 2, 56126 PISA (Italy)
fax: +39-50-568522           |  http://www.iet.unipi.it/~luigi/
_____________________________|______________________________________



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