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ANerd

Member

Registered: 2012-03-05

Posts: 1

Pulseaudio digital input drift

Hi

I have an USB sound card with IEC958 (optical) input. I then use module-loopback to loop the sound back to the analog output on the same card. Works great to begin with, but after a while the latency increases. After ~10h the latency is ~30s. I tried the "latency_msec" option, but it only affects the latency to begin with, it still drifts. In "pactl list" the "Buffer Latency" under module-looback's Sink Input is consistent with the latency I hear. If I unload and load the loopback module, the latency disappears, but after a while gradually returns. After searching the web I found that a probable cause of the problem is that the IEC958 input uses the clock of the device in the other end of the cable (in my case a tv), so even if both run at 48kHz, there is drift between the two clocks (30s/10h=0.08% drift). I have found that I probably need to resample the signal, but have not found a way to force that.

So my question is, how do I force module-loopback/IEC958source to resample? Eventually, force module-loopback to drop samples when delay becomes too large?

Anders