Re: [ecasound] ecsound recording time

Am 15.04.2009 19:48, Kai Vehmanen schrieb:
> Hi,
>
> 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?
I start recording with cron at e.g. 00:04 for exactly 116,5 minutes, so
it should just catch the 2 o'clock news

>
> What's the file size (in bytes) of "x.wav" after recording? It should
Filesize matches nearly exact.
> 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).

Recording comes from a Sat-Receiver ( a nightly classical concert by
german ARD-stations )

maybe the error results from transcoding to 44,100 , if I correct the
minute to 65,2 secs the recording time is as expected.

Thanks a lot for Your answer,

K. Müller

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Received on Fri Apr 17 00:15:01 2009