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Audio Underflow's effect on latency

JM
John M
Thu, Jun 15, 2017 7:19 PM

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 frame

17:59:27.446    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.

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 frame 17:59:27.446 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.
BG
Bill Gardner
Thu, Jun 15, 2017 7:55 PM

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 frame

17:59:27.446 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.

Visit our blog: http://blog.pjsip.org

pjsip mailing list
pjsip@lists.pjsip.org
http://lists.pjsip.org/mailman/listinfo/pjsip_lists.pjsip.org

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 frame > > 17:59:27.446 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. > > > > _______________________________________________ > Visit our blog: http://blog.pjsip.org > > pjsip mailing list > pjsip@lists.pjsip.org > http://lists.pjsip.org/mailman/listinfo/pjsip_lists.pjsip.org
JM
John M
Thu, Jun 15, 2017 8:42 PM

Thanks for the quick response.

Our input and output are both powered by the same master clock. They
communicate to the system over USB Audio though. Could it be possible
timing issues in USB transmission can cause a similar issue?

On Jun 15, 2017 3:56 PM, "Bill Gardner" billg@wavearts.com wrote:

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 frame

17:59:27.446    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.

Visit our blog: http://blog.pjsip.org

pjsip mailing listpjsip@lists.pjsip.orghttp://lists.pjsip.org/mailman/listinfo/pjsip_lists.pjsip.org

Visit our blog: http://blog.pjsip.org

pjsip mailing list
pjsip@lists.pjsip.org
http://lists.pjsip.org/mailman/listinfo/pjsip_lists.pjsip.org

Thanks for the quick response. Our input and output are both powered by the same master clock. They communicate to the system over USB Audio though. Could it be possible timing issues in USB transmission can cause a similar issue? On Jun 15, 2017 3:56 PM, "Bill Gardner" <billg@wavearts.com> wrote: > 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 frame > > 17:59:27.446 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. > > > _______________________________________________ > Visit our blog: http://blog.pjsip.org > > pjsip mailing listpjsip@lists.pjsip.orghttp://lists.pjsip.org/mailman/listinfo/pjsip_lists.pjsip.org > > > > _______________________________________________ > Visit our blog: http://blog.pjsip.org > > pjsip mailing list > pjsip@lists.pjsip.org > http://lists.pjsip.org/mailman/listinfo/pjsip_lists.pjsip.org > >
BG
Bill Gardner
Thu, Jun 15, 2017 8:55 PM

USB can't alter the audio sampling rate, but if the audio buffers don't
keep up then a missing record buffer would also trigger wsola
reconstruction. If you increase the audio buffer sizes does the latency
become more stable? Ideally the record and playback buffer callbacks
should alternate, but often you will get repeats (bursts), depending on
platform and audio device. Perhaps you are getting a repeat playback
every 5 seconds causing the record buffer to underflow.

On 6/15/2017 4:42 PM, John M wrote:

Thanks for the quick response.

Our input and output are both powered by the same master clock. They
communicate to the system over USB Audio though. Could it be possible
timing issues in USB transmission can cause a similar issue?

On Jun 15, 2017 3:56 PM, "Bill Gardner" <billg@wavearts.com
mailto:billg@wavearts.com> wrote:

 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 frame

 17:59:27.446 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.



 _______________________________________________
 Visit our blog:http://blog.pjsip.org

 pjsip mailing list
 pjsip@lists.pjsip.org <mailto:pjsip@lists.pjsip.org>
 http://lists.pjsip.org/mailman/listinfo/pjsip_lists.pjsip.org
 <http://lists.pjsip.org/mailman/listinfo/pjsip_lists.pjsip.org>

 _______________________________________________
 Visit our blog: http://blog.pjsip.org

 pjsip mailing list
 pjsip@lists.pjsip.org <mailto:pjsip@lists.pjsip.org>
 http://lists.pjsip.org/mailman/listinfo/pjsip_lists.pjsip.org
 <http://lists.pjsip.org/mailman/listinfo/pjsip_lists.pjsip.org>

Visit our blog: http://blog.pjsip.org

pjsip mailing list
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USB can't alter the audio sampling rate, but if the audio buffers don't keep up then a missing record buffer would also trigger wsola reconstruction. If you increase the audio buffer sizes does the latency become more stable? Ideally the record and playback buffer callbacks should alternate, but often you will get repeats (bursts), depending on platform and audio device. Perhaps you are getting a repeat playback every 5 seconds causing the record buffer to underflow. On 6/15/2017 4:42 PM, John M wrote: > Thanks for the quick response. > > Our input and output are both powered by the same master clock. They > communicate to the system over USB Audio though. Could it be possible > timing issues in USB transmission can cause a similar issue? > > On Jun 15, 2017 3:56 PM, "Bill Gardner" <billg@wavearts.com > <mailto:billg@wavearts.com>> wrote: > > 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 frame >> >> 17:59:27.446 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. >> >> >> >> _______________________________________________ >> Visit our blog:http://blog.pjsip.org >> >> pjsip mailing list >> pjsip@lists.pjsip.org <mailto:pjsip@lists.pjsip.org> >> http://lists.pjsip.org/mailman/listinfo/pjsip_lists.pjsip.org >> <http://lists.pjsip.org/mailman/listinfo/pjsip_lists.pjsip.org> > > > _______________________________________________ > Visit our blog: http://blog.pjsip.org > > pjsip mailing list > pjsip@lists.pjsip.org <mailto:pjsip@lists.pjsip.org> > http://lists.pjsip.org/mailman/listinfo/pjsip_lists.pjsip.org > <http://lists.pjsip.org/mailman/listinfo/pjsip_lists.pjsip.org> > > > > _______________________________________________ > Visit our blog: http://blog.pjsip.org > > pjsip mailing list > pjsip@lists.pjsip.org > http://lists.pjsip.org/mailman/listinfo/pjsip_lists.pjsip.org
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