[pulseaudio-discuss] {PATCH][RFC] AC3 passthrough support

Michael Rans mcarans at yahoo.co.uk
Tue Jul 13 14:28:04 PDT 2010

Strange - $CARD really won't work on my setup - it fails to create an a52 
device. Can anyone else get it working? On Lucid?

I tried it in ~/.asoundrc, /etc/asound.conf and /usr/share/alsa/alsa.conf and no 


From: pl bossart <bossart.nospam at gmail.com>
To: General PulseAudio Discussion <pulseaudio-discuss at mail.0pointer.de>
Sent: Tue, 13 July, 2010 21:21:50
Subject: Re: [pulseaudio-discuss] {PATCH][RFC] AC3 passthrough support

Adding this in /etc/asound.rc (more exactly
/etc/alsa/pulse-default.conf on my Fedora box) work fine:

pcm.a52 {
   @args [CARD]
   @args.CARD {
       type string
   type rate
   slave {
       pcm {
           type a52
           bitrate 448
           channels 6
           card $CARD
       rate 48000 #required somehow, otherwise nothing happens in PulseAudio

a52:0 is detected by PulseAudio and the encoded output shows as
'Digital Surround 5.1 (IEC958/AC3) in pavucontrol.

I just finished testing all the changes I posted yesterday. Works
flawlessly, I can switch from 2ch PCM over SPDIF to 5.1 still over
SPDIF but re-encoded with a52, and unlike the passthrough case I can
mix the multichannel content with alerts or system tones.
The only bug I found is that if I change the individual volume on one
of the channels, there's a ringing noise introduced, and it does not
go away unless I kill the stream.

Will prepare a set of patches, Colin it'd be great if you can merge
them in git master.
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