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Date:      Tue, 23 Dec 1997 05:23:35 +0100 (MET)
From:      Luigi Rizzo <luigi@labinfo.iet.unipi.it>
To:        hasty@rah.star-gate.com (Amancio Hasty)
Cc:        hasty@rah.star-gate.com, steve@visint.co.uk, multimedia@freebsd.org
Subject:   Re: precise soundcard tuning ?
Message-ID:  <199712230423.FAA03728@labinfo.iet.unipi.it>
In-Reply-To: <199712222115.NAA02470@rah.star-gate.com> from "Amancio Hasty" at Dec 22, 97 01:15:21 pm

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> Strange, according to Jim's test program my guspnp is about
> .002 accurate.
> 520000 64.9858 8001.75
> 528000 65.9856 8001.75
> 536000 66.9854 8001.74

quite reasonable result (I assume that you have run the test for a
much longer time,  or the 200us differences that you see are not that
significant).

But the problem is that some sampling rates might not be so precise
(due to the sample rate not being an exact divisor of the XTAL
frequency) and these differences accumulate over time. The problem is
often worse at high sampling rates (where you need a smaller divisor).
Even in your case, you have a drift of roughly 1 second/hour.

	Cheers
	Luigi



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