Hi John,
It's likely a mismatch in the sampling rates of the record and playback devices. Unless they are using the same hardware clock there will be drift and hence the wsola delay buf is necessary to prevent discontinuities.
Regards,
Bill
On 6/15/2017 3:19 PM, John M wrote:
Hello all,
I am developing a Voip product with a max latency requirement of 150ms mouth to ear. Our current tests show latency moving in a saw-tooth like pattern between 180ms and 140ms.
The latency will begin at ~180ms, and then drop over time to around 160 to 140ms. Then, it jumps back up to ~180 and the process repeats.
This is all measured using oscilloscopes and similar instruments. Running the pjsua application with a call to sip:localhost shows no sawtooth pattern, and a call between two COTS Voip phones do not show the sawtooth pattern.
What I recognized was that the latency would jump back up after a buffer underflow on a split combo port:
17:59:27.446 scombdb-dn !Underflow, buf_cnt=1, will generate 1 frame17:59:27.446 scombdb-dn Underflow, buf_cnt=126, will generate 1 frame
17:59:33.246 scombdb-dn Underflow, buf_cnt=1, will generate 1 frame
17:59:33.246 scombdb-dn Underflow, buf_cnt=126, will generate 1 frame
17:59:38.365 scombdb-dn Underflow, buf_cnt=1, will generate 1 frame
17:59:38.366 scombdb-dn Underflow, buf_cnt=126, will generate 1 frame
17:59:44.486 scombdb-dn Underflow, buf_cnt=1, will generate 1 frame
17:59:44.486 scombdb-dn Underflow, buf_cnt=126, will generate 1 frame
17:59:49.626 scombdb-dn Underflow, buf_cnt=1, will generate 1 frame
17:59:49.626 scombdb-dn Underflow, buf_cnt=126, will generate 1 frame
17:59:55.426 scombdb-dn Underflow, buf_cnt=1, will generate 1 frame
17:59:55.426 scombdb-dn Underflow, buf_cnt=126, will generate 1 frame
18:00:06.686 scombdb-dn Underflow, buf_cnt=1, will generate 1 frame
18:00:06.687 scombdb-dn Underflow, buf_cnt=126, will generate 1 frame
18:00:12.486 scombdb-dn Underflow, buf_cnt=1, will generate 1 frame
18:00:12.487 scombdb-dn Underflow, buf_cnt=126, will generate 1 frame
18:00:17.926 scombdb-dn Underflow, buf_cnt=1, will generate 1 frame
18:00:17.926 scombdb-dn Underflow, buf_cnt=126, will generate 1 frame
… some time later …
18:03:39.166 scombdb-dn Underflow, buf_cnt=121, will generate 1 frame
18:03:39.166 scombdb-dn Underflow, buf_cnt=21, will generate 1 frame
18:03:44.646 scombdb-dn Underflow, buf_cnt=121, will generate 1 frame
18:03:44.646 scombdb-dn Underflow, buf_cnt=21, will generate 1 frame
18:03:49.766 scombdb-dn Underflow, buf_cnt=121, will generate 1 frame
18:03:49.766 scombdb-dn Underflow, buf_cnt=21, will generate 1 frame
This reliably happens every 5 to 6 seconds.
What could be causing this underflow? We are looking for minimum latency, so the jitter buffer is at a max of 60ms and the sound device has a play and record latency of 40ms.
Any guidance would be appreciated.
Thanks,
John.
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