[alsa-devel] Alsa Crackling Noise

[Dinesh Ravindran]

anyone else?? some clue about how to approach this problem?


best regards
Dinesh

On Mon, Nov 9, 2015 at 4:29 PM, Caleb Crome <caleb at crome.org> wrote:

> On Fri, Nov 6, 2015 at 9:27 AM, Dinesh Ravindran <rite2dinesh at gmail.com>
> wrote:
> > The USB soundcard natively supports the sampling rate of 8kHz. We tried
> with
> > all three options of the kernel preemption model, and it doesn't make any
> > difference. The CPU utilization is almost zero, and interestingly when
> the
> > CPU consumption is high the audio sounds better(we notice when we copy a
> > file via ssh, cpu consumption goes upto 33%).
> >
> > The default premption model is set to none, however we tried with both
> > voluntary and Low-Latency Desktop, it doesn't make any difference.
> >
> > One thing we noticed was that even though from our application(or aplay)
> we
> > set the access to SND_PCM_ACCESS_RW_INTERLEAVED,
> > /proc/asound/card0/pcm0p/sub0/hw_params shows it as MMAP_INTERLEAVED,
> we're
> > not sure why it is so and what the impact could be.
> >
> > Does it has to do with the low level USB transfer, where it it waiting
> for
> > more data to transfer it in one shot,  because, at higher sampling rate
> we
> > have more data to transfer. But it still doesn't explain why printing
> some
> > debug statements or having a larger alsa buffer works.
> >
> >
>
> That is certainly strange.  Sorry I don't know how to help.  Perhaps
> somebody else can shed some light.
>
> -Caleb
>
>
>
> >
> >
> > best regards
> > Dinesh
> >
> > On Fri, Nov 6, 2015 at 5:37 PM, Caleb Crome <caleb at crome.org> wrote:
> >>
> >> On Fri, Nov 6, 2015 at 1:59 AM, Dinesh Ravindran <rite2dinesh at gmail.com
> >
> >> wrote:
> >> > We have been facing a weird issue with Alsa recently. Sometimes the
> >> > audio
> >> > plays out with out any noise and sometimes it has lot of cracking
> noise,
> >> > really a lot. The weird situation is when another application is
> >> > printing
> >> > out some debug statements to a console it sounds good. The behavior is
> >> > same
> >> > with a custom developed alsa application and also with aplay. Any
> >> > thoughts?
> >> > If we have a really big buffer size of around 2sec it works somehow,
> but
> >> > we
> >> > really want to analyze why alsa exhibits this strange behavior. Is it
> >> > the
> >> > alsa itself or is it just a symptom of a bigger issue at system level?
> >> >
> >> > All the test we are carrying out it at 8KHz, at higher sampling
> >> > rate(48k)
> >> > we do not see this behaviour.
> >> >
> >> >
> >> > These are the scenarios in which it sounds good:
> >> > 1. If any application is printing to the console while audio is being
> >> > played out or even just holding the return button on the console
> helps.
> >> > 2. If we enable xrun debug with echo 29 >
> >> > /proc/asound/card0/pcm0p/xrun_debug it sounds good.
> >> > 3. If we have really big buffer size around 2 seconds.
> >> > 4. Or sometimes on fresh start of the machine until it enters xrun
> state
> >> > once.
> >> >
> >> >
> >> >
> >> > We have the following setup:
> >> >
> >> > Processor: ARM926EJ-S
> >>
> >> What's your CPU utilization when playing 8kHz?  It's interesting that
> >> 48kHz has no problem, but 8kHz does.  My first guess would be that
> >> alsa is forced to resample in software, causing the cpu load to go up.
> >>    Do you know what rates your actual codec can run at?
> >>
> >> Others on this list are infinitely more likely to know the true answer
> :-)
> >>
> >> Another question: what's the preemption model in your kernel config?
> >> under kernel features->Preemption model?  You can also check your
> >> .config for CONFIG_PREEMPT=y
> >>
> >> -Caleb
> >>
> >> > Kernel: 3.14.53
> >> > Alsa-lib: 1.0.29
> >> > Alsa-Util: 1.0.29
> >> > Audio Chip: CONEXANT USB AUDIO
> >> >
> >> >> aplay -Dplughw:0,0 8kz_8000.wav  #to play file
> >> >
> >> >
> >> > cat /proc/asound/card0/stream0
> >> > ----------------------------------------
> >> >
> >> > Playback:
> >> >   Status: Stop
> >> >   Interface 2
> >> >     Altset 1
> >> >     Format: S16_LE
> >> >     Channels: 2
> >> >     Endpoint: 1 OUT (ADAPTIVE)
> >> >     Rates: 8000, 16000, 24000, 32000, 44100, 48000
> >> >
> >> > Hw params:
> >> > --------------
> >> >
> >> > access: MMAP_INTERLEAVED
> >> > format: S16_LE
> >> > subformat: STD
> >> > channels: 2
> >> > rate: 8000 (8000/1)
> >> > period_size: 1000
> >> > buffer_size: 4000
> >> >
> >> > sw params:
> >> > -------------
> >> >
> >> > tstamp_mode: NONE
> >> > period_step: 1
> >> > avail_min: 1000
> >> > start_threshold: 4000
> >> > stop_threshold: 4000
> >> > silence_threshold: 0
> >> > silence_size: 0
> >> > boundary: 2097152000
> >> >
> >> > status:
> >> > --------
> >> >
> >> > state: RUNNING
> >> > owner_pid   : 1852
> >> > trigger_time: 3667.436640852
> >> > tstamp      : 3756.680343977
> >> > delay       : 3296
> >> > avail       : 720
> >> > avail_max   : 1000
> >> > -----
> >> > hw_ptr      : 712720
> >> > appl_ptr    : 716000
> >> > _______________________________________________
> >> > Alsa-devel mailing list
> >> > Alsa-devel at alsa-project.org
> >> > http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
> >
> >
>