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audio-video asynchrony with a USB soundcard



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.

To summarise:
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,
m