[pulseaudio-discuss] need help with audio sync

golden magic.lixin at gmail.com
Wed May 6 01:51:36 PDT 2015

Dear Georg,

   thanks for the answers, I really like your 2nd solution.

   But the problem is, add a another module-loopback in front speaker 
path, which means I need a another
   pair of alsa drivers (as alsa-sink.0 and alsa-source.0 in the pic), 
that what I have written to the
   alsa device, then I can read the data back from the input alsa 
device. It`s not a valid solution with our
   current hardware.

   also another problem is that: we support dynamic switch the sink of 
the pa_stream (pa_sink_input_move_to)
   we have 3 way to playback current stream:

   1. front speaker path only
      pa_stream -> alsa-sink.1 -> front-speaker

   2. rear speaker path only
      pa_stream -> alsa-sink.0 -> alsa-source.0 -> alsa-sink.2 (within a 
module-loopback )

   3. front and rear speaker combine
      pa_stream -> combine-sink -> alsa-sink.1 -> front-speaker

                                -> alsa-sink.0 -> alsa-source.0 -> 
alsa-sink.2 (within a module-loopback )

   I`m not sure may be I can add a fake a module-loopback, just memory 
copy but wait for a while to simluate the lantency ?

   Thanks anyway!


在 2015年05月06日 14:05, Georg Chini 写道:
> On 06.05.2015 04:17, golden wrote:
>> Dear PulseAudio folks,
>>       We are using PulseAudio in our automotive project, the progress is pretty good so far.
>>       I need some help for solving the sync problems between two speakers.
>>      The pic below is the data flow of the two speakers:
>>     without any syncing method, what we hear from the front-speaker 
>> is ahead of the rear-speaker (real-spear is slower for sure), our 
>> goal is that make the rear-speaker almost sync with (or catch up) the 
>> front speaker.
> Hi,
> with your manipulation of the audio and with module-loopback you 
> introduce quite a lot of latency into the
> first path. Maybe you can simply set the latency of alsa-sink.1 larger 
> than that of alsa-sink.0, not sure if this works.
> Otherwise I would suggest to make the paths look more or less 
> equivalent, that would mean putting a
> module-loopback into the front speaker path.
> You could also try and use my (not yet reviewed) patches for 
> module-loopback at
> http://thread.gmane.org/gmane.comp.audio.pulseaudio.general/22956
> which allow a better control over the latency introduced by the module.
> If you use the patches and have a module-loopback in both paths you 
> should be able to fully synchronize
> them by adjusting the latencies of the two modules.
> Regards
>             Georg
> _______________________________________________
> pulseaudio-discuss mailing list
> pulseaudio-discuss at lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/pulseaudio-discuss

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