[pulseaudio-discuss] xine 5.1 channel downmix

[Nikolaus Filus]

Nikolaus Filus wrote:
> Hi,
> 
> Lennart Poettering wrote:
>> On Fri, 11.05.07 18:06, Nikolaus Filus (nfilus at gmx.net) wrote:
>>
>>> Ok, so now I confirmed the channel maps are different. But where can I downmix
>>> 5.1 to 2? Where can I read more about possible setups?
>>> - configure sink for 5.1 (my notebook can't do that, but this would be nice-to-know)
>>> - downmix channels
>>> - select n channels and pass to sink
> 
>> PA will not downmix channels. It will only copy or drop
>> channels. Channels are mapped by names. I.e. if a sink has
>> fron-left,front-right,lfe and a stream just has
>> front-left,front-right, then the lfe will get silence. The only
>> special rule is that we mix front-left+front-right into mono, and copy
>> mono to front-left and front-riught.
>>
>> In essence: the rules are vey basic. We don't do any dolby surround
>> coding. No lowpass filtering for LFE. (Which btw, is another item on my todo list)
> 
> So I figured out, it is possible to downmix (and upmix) channels in ALSA by
> using the following definition in asound.conf
> 
> pcm.51to20 {
>      type route
>      slave.pcm default
>      slave.channels 6
>      ttable.0.0 1      # front left -> left
>      ttable.1.1 1      # front right -> right
>      ttable.2.0 0.707  # hinten left -> left, gain 3dB
>      ttable.3.1 0.707  # hinten right -> right, gain 3dB
>      ttable.4.0 0.5    # center -> left, gain 6dB
>      ttable.4.1 0.5    # center -> right, gain 6dB
>      ttable.5.0 0.5    # LFE -> left, gain 6dB
>      ttable.5.1 0.5    # LFE -> right, gain 6dB
> }
> ctl.51to20 {
>   type hw
>   card 0
> }
> 
> xine [pulse, 5.1] -> pulseaudio [sink:51to20] -> alsa [pcm.51to20]
> -> alsa [default] -> alsa [hw:0,0 aka intel8x0]
> 
> This kinda works, so that I can change the volume of each stream channel
> independantly in pavucontrol and hear the effect on my speakers. BUT now
> pulseaudio has a much higher load and the sound isn't clear so I hear cracking
> noises. My only guess is, that pulseaudio shows the sink as
> "ALSA PCM on 51to20 (dmix:0)" and I don't know why it identifies it as dmix.
> 
> Any hints or tweaks?

One week passed and no answers yet. Is there anyone having an idea?


Nikolaus