Re: [ecasound] ecsound recording time

From: Kai Vehmanen <kvehmanen@email-addr-hidden>
Date: Wed Apr 15 2009 - 20:48:55 EEST


On Tue, 14 Apr 2009, kjm wrote:

> when I record a 2 hour session with
> /usr/bin/ecasound -D -t:7200 -f:32,2,48000 -i alsa,ice_spdif -o "x.wav"
> the recorded file shows 120 min. length in audacity,
> but it is about 6 minutes shorter then the requested 120 minutes.

if both ecasound and audacity show the length to be 120min, how do you
know it's exactly 6min shorter than it should be?

What's the file size (in bytes) of "x.wav" after recording? It should
be 2764800044 (4*2*48000*7200 plus a 44byte RIFF header).

A small error is certainly possible, because both ecasound and audacity
measure time in terms of audio samples (48000 samples = 1 sec), and this
can be slightly different than actual wall-clock time due to clock skew
introduced by the ADC/DAC sample clock. This also means if you play the
same audio file with two different soundcards, the playback time may be
slightly different.

But 6min in two hours is a _huge_ difference, and it seems very unlikely
that this is caused by clock skew.

> I use a M-Audio 2496 with spdif-in, which has 48000 fixed.

Hmm, where are you recording from? As this comes digitally over spdif, the
possibly clock skew is created at the source (i.e. M-Audio 2496 is not to
blame here).

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Received on Thu Apr 16 00:15:01 2009

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