[pulseaudio-discuss] Channel Mapping

Another Sillyname anothersname at googlemail.com
Mon Jun 9 11:42:59 PDT 2008

Hi and thanks for the quick response.....

Yep I am using ALSA but I don't understand your answer (because I'm thick!).

Are you saying that each time ALSA plays a different AC3 source the
mapping can be different or that it's always consistently wrong the
same way?

If it's consistently wrong the same way I should be able to identify
which channel is mapping to which channel (I've got an AC3 test avi
that shows where the source should be coming from while it's playing

In effect my system takes all the source material (including wavs and
MP3's) and runs it through an A52encode before pumping it out to an
external amp via spdif.  I've set it up this way to minimise the
amount of interaction I need to do that source material dependent.  If
I could get the AC3 material working properly then that would make my

Thanks and regards


2008/6/9 Lennart Poettering <lennart at poettering.net>:
> On Mon, 09.06.08 19:28, Another Sillyname (anothersname at googlemail.com) wrote:
>> Hi
>> I've read from assorted sources that accurate channel mapping of a AC3
>> stream through a A52encode to then produce output just doesn't work
>> correctly?
>> Is this still the case or is there a method to be able to work out
>> which channel in the original stream should map to which channel on
>> the output then be able to configure pulseaudio to output correctly?
>> At the moment the front left/right appear to be coming out the rear
>> and the centre seems to be coming from the left/right front
>> speakers........rear and woofer sounds don't appear at all!!
> I am not sure about your specific setup. But PA allows you to specify
> an explicit channel map for an alsa sink. Also, PA takes negotiates
> the channel map with its clients.
> So, which client are you using? If you access PA through ALSA, then I
> guess I can only say I am sorry: ALSA does not support negotiating
> channel maps. For ALSA you need to *know* the channel map of a
> device.
> Lennart
> --
> Lennart Poettering                        Red Hat, Inc.
> lennart [at] poettering [dot] net         ICQ# 11060553
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