From owner-freebsd-multimedia Mon Dec 22 10:44:38 1997 Return-Path: Received: (from root@localhost) by hub.freebsd.org (8.8.7/8.8.7) id KAA14951 for multimedia-outgoing; Mon, 22 Dec 1997 10:44:38 -0800 (PST) (envelope-from owner-freebsd-multimedia) Received: from labinfo.iet.unipi.it (labinfo.iet.unipi.it [131.114.9.5]) by hub.freebsd.org (8.8.7/8.8.7) with SMTP id KAA14822 for ; Mon, 22 Dec 1997 10:42:35 -0800 (PST) (envelope-from luigi@labinfo.iet.unipi.it) Received: from localhost (luigi@localhost) by labinfo.iet.unipi.it (8.6.5/8.6.5) id RAA02728; Mon, 22 Dec 1997 17:41:25 +0100 From: Luigi Rizzo Message-Id: <199712221641.RAA02728@labinfo.iet.unipi.it> Subject: Re: precise soundcard tuning ? To: hasty@rah.star-gate.com (Amancio Hasty) Date: Mon, 22 Dec 1997 17:41:25 +0100 (MET) Cc: steve@visint.co.uk, multimedia@freebsd.org In-Reply-To: <199712221733.JAA01209@rah.star-gate.com> from "Amancio Hasty" at Dec 22, 97 09:33:31 am X-Mailer: ELM [version 2.4 PL23] Content-Type: text Sender: owner-freebsd-multimedia@freebsd.org X-Loop: FreeBSD.org Precedence: bulk > 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/ _____________________________|______________________________________