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Re: audio-video asynchrony with a USB soundcard
you didn't tell what kind of audio driver you are using. I assume that
all of your tests are done on a windows platform (correct me if I'm
One important parameter is the kind of audio driver you use. To
increase accuracy of latency, you should use the ASIO Driver on which
you'll be able to set the buffers size which determine the audio
latency : a buffer size of 128 samples with a sampling rate of 44.1kHz
leads to a 2.9 ms latency. The results should be consistent with asio
driver, the only uncertainty being the time between you display &
soundplay function calls.
The standard windows driver (WME) is quite unaccurate in terms of
Hope this helps
Le 5 déc. 08 à 14:03, Massimo Grassi a écrit :
Dear list members,
I measured yesterday the audio-video asynchrony with an USB sound
card (M-AUDIO Fast Track Pro).
In practice, I was running a visual display and, in correspondence of
one particular video-target-frame, I was switching on a 1-cycle sine
wave (1000 Hz). I checked whether the video-frame and the audio
signal were synchronous.
In general, the video preceded always the audio (although, if any, I
had to expect the opposite result because in the program the
soundplay command preceded the play the video-target-frame command).
The average video-anticipation was of 6.3-ms (SD=3.0, maximal video
anticipation 12-ms, min=2-ms). I forgot: the video was running at
100-Hz refresh rate.
1) audio and video signals are often asynchronous;
2) the asynchrony (unfortunately) does not have a fixed value but
changes within a certain range.
It is not as bad as I was expecting but with a PCI sound card (a
very cheap one) and identical set-up I observed an average
asynchrony of 2-ms (SD<4-ms).
All the best,
JE 2497 "Neuropsychologie et Cognition Auditive"
Université de Lille 3,UFR de Psychologie
59653 Villeneuve d’Ascq Cedex
Phone: +33 3 20 41 64 42
Fax: +33 3 20 41 63 24