From owner-freebsd-multimedia Mon Dec 22 10:24:28 1997 Return-Path: Received: (from root@localhost) by hub.freebsd.org (8.8.7/8.8.7) id KAA13087 for multimedia-outgoing; Mon, 22 Dec 1997 10:24:28 -0800 (PST) (envelope-from owner-freebsd-multimedia) Received: from rah.star-gate.com (rah.star-gate.com [204.188.121.18]) by hub.freebsd.org (8.8.7/8.8.7) with ESMTP id KAA13080 for ; Mon, 22 Dec 1997 10:24:26 -0800 (PST) (envelope-from hasty@rah.star-gate.com) Received: from rah.star-gate.com (localhost.star-gate.com [127.0.0.1]) by rah.star-gate.com (8.8.8/8.8.8) with ESMTP id KAA01505; Mon, 22 Dec 1997 10:23:28 -0800 (PST) (envelope-from hasty@rah.star-gate.com) Message-Id: <199712221823.KAA01505@rah.star-gate.com> X-Mailer: exmh version 2.0gamma 1/27/96 To: Luigi Rizzo cc: steve@visint.co.uk, multimedia@freebsd.org, Jim Lowe Subject: Re: precise soundcard tuning ? In-reply-to: Your message of "Mon, 22 Dec 1997 17:41:25 +0100." <199712221641.RAA02728@labinfo.iet.unipi.it> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Date: Mon, 22 Dec 1997 10:23:28 -0800 From: Amancio Hasty Sender: owner-freebsd-multimedia@freebsd.org X-Loop: FreeBSD.org Precedence: bulk Just talk to Jim he is the real pro on all these issues and yes the PC clock depending upon your motherboard can also affect you provided of course that you are using it to derive your clock info. ASUS motherboards generally provide a good RTC -- I think they use a Dallas Semiconductor RTC part. ---- Hi Jim, The clock accuracy issue is surfing up again . Any info on new hardware or method which provides accurate clock rates from sound cards also any known good motherboards with a decent RTC or cheap external clocks which can provide a resonable accurate clock? Tnks, Amancio > > 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/ > _____________________________|______________________________________