[pulseaudio-discuss] a question about audio synchronization between local sink and tunnel sink

Sun, Xiaodong xisun at qca.qualcomm.com
Mon Oct 15 10:55:56 PDT 2012

Hi, Daniel,

Do you ever get synchronized playback on your system? 
My concern is, pulseaudio module-combine-sink may not designed for synchronized playback at all. That is why sometimes people see synchronized playback and some doesn't. It really depends on latency of different device.


-----Original Message-----
From: pulseaudio-discuss-bounces+xisun=qca.qualcomm.com at lists.freedesktop.org [mailto:pulseaudio-discuss-bounces+xisun=qca.qualcomm.com at lists.freedesktop.org] On Behalf Of Daniël Sonck
Sent: Sunday, October 14, 2012 1:13 PM
To: General PulseAudio Discussion
Subject: Re: [pulseaudio-discuss] a question about audio synchronization between local sink and tunnel sink

I'll add some of my findings. I have some special system that connects several tunnels to computers. When I start some music, the local sound card actually is the one behind the network sink. I do remember that sometimes the network sink stops to get in sync with the local soundcard.

But you'll always have some noticeable delay, simply because you'll probably have two different sound cards.

On a side note, when I had a bug in my system which allowed two tunnels from my server to the same client it actually caused a flange effect. 
That indicates that it always has a different delay and apparently it doesn't wait for the exact moment to play it back. I think this is the most significant indication that you won't be able to have an exactly synchronized playback. I currently use this to have music in different rooms where you can close a door, or you don't hear the music from other rooms.


On Sun 14 Oct 2012 07:19:41 PM CEST, Tanu Kaskinen wrote:
> On Wed, 2012-10-10 at 20:45 +0000, Sun, Xiaodong wrote:
>> Hi,
>> I have a pulseaudio daemon running on one PC (with my music songs 
>> stored and played on this PC, let's call it PC-1). And then I setup 
>> another PC (let's call it PC-2) running pulseaudio daemon on it and 
>> enabled native TCP protocol. Then I configured (by using pacmd) PC-1 
>> pulseaudio to load a tunnel sink pointing to PC-2, and then loaded a 
>> combine sink which combines PC-2 tunnel sink and PC-1 local analog 
>> audio sink. Now I can hear audio from both PC-1 and PC-2 at the same 
>> time. But the audio playing are not synchronized between PC-1 and 
>> PC-2. There is a delay on PC-2 comparing with PC-1.
>> Now my question is, is pulseaudio designed for synchronized playback 
>> between local sink and tunnel sink? If yes, what kinds of parameters 
>> should I tune?
> I had a look, and it seems like module-tunnel is tries to report 
> pretty accurate latency, and module-combine-sink in turn is supposed 
> to synchronize the outputs if they provide valid latency information. 
> So it looks like this should work, without any parameter tuning.
> Unfortunately, if it doesn't work, I don't have much ideas for making 
> it work. How big is the delay between the two outputs? If you let it 
> play for a while, does it get better?

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