8 independants mono channel on 7.1 sound card, but possibility to play sound on 8 channels simultaneously

Question

For a personal sound project with a raspberry PI 3 and an USB 7.1 channel sound card, I need to use the sound card as 8 independents mono channels, to play different mono sounds on specifics channel. And sometime 2 or more mono sounds car be played (mixed) in the same time on a given channel. I finally found the way to do that in my .asoundrc configuration file :

pcm_slave.usbsoundcard {
pcm "hw:1"
rate 44100
channels 8
periods 128
period_time 0
period_size 1024
buffer_time 0
buffer_size 4096
}

pcm.ch1 {
type dmix
slave usbsoundcard
ipc_key 1001
bindings [ 0 ]
}

pcm.ch2 {
type dmix
slave usbsoundcard
ipc_key 1001
bindings [ 1 ]
}

pcm.ch3 {
type dmix
slave usbsoundcard
ipc_key 1001
bindings [ 6 ]
}

pcm.ch4 {
type dmix
slave usbsoundcard
ipc_key 1001
bindings [ 7 ]
}

pcm.ch5 {
type dmix
slave usbsoundcard
ipc_key 1001
bindings [ 2 ]
}

pcm.ch6 {
type dmix
slave usbsoundcard
ipc_key 1001
bindings [ 3 ]
}

pcm.ch7 {
type dmix
slave usbsoundcard
ipc_key 1001
bindings [ 4 ]
}

pcm.ch8 {
type dmix
slave usbsoundcard
ipc_key 1001
bindings [ 5 ]
}

With this config file, I can play what I want on the channel I want, and I can play multiple sound in same time on each independent channel if needed with commands like this:

aplay -D plug:ch3 sound1_mono.wav &
aplay -D plug:ch3 sound2_mono.wav &  # sound 2 mixed with sound 1 on channel 3
aplay -D plug:ch7 sound3_mono.wav &
aplay -D plug:ch8 sound4_mono.wav &

etc...

But I want to add another possibility. I want to add a virtual channel named "all", which must route the played sound on ALL 8 mono channels. The final goal is to configure Asterisk pbx system configured as intercom to use this channel : when called, Asterisk will autoanswer, and I want voice routed (mixed) on all 8 channels of the sound card.

I naively tried that :

pcm.all {
type dmix
slave usbsoundcard
ipc_key 1001
bindings [ 0 1 2 3 4 5 6 7 ]
}

But it doesn't work. For testing I also play a mono sound on the 'all' virtual channel. If I do : aplay -D plug:all sound5_mono.wav The sound is correctly played on all channel ch1... ch8 where no other wav file is played. But on channel where a sound is already played, can't hear sound5_mono. wav but I have crackling noices

How can I write my. asoundrc file to have it working ? What I want to do is a kind of audio multiroom : play differents mono file on each channel ch1.... ch8 in differents room, and when I call the raspberry with a SIP phone, voice is played (mixed) in all rooms.

Answer 1

I'm not sure if you can use different dmix definitions with the same ipc_key; it might be a better idea to use a common dmix device.

To be able to play a stero file to all channels, you have to convert it to mono first.

pcm.dmix8 {
    type dmix
    slave {
        pcm "hw:1"
        rate 44100
        channels 8
        period_size 1024
        buffer_size 32768
    }
}

pcm.ch1 {
    type plug
    slave.pcm dmix8
    ttable.0.0 1
}
pcm.ch2 {
    type plug
    slave.pcm dmix8
    ttable.0.1 1
}
# and so on with "ttable.0.x 1"

pcm.all {
    type plug
    slave {
        pcm {
            type route
            slave.pcm dmix8
            ttable [ [ 1 1 1 1 1 1 1 1 ] ]
        }
        channels 1
    }
}

Answer 2

even if your last proposition doesn't work for virtual channel "all", it helped me a lot, and I tried something which works perfectly on my computer, with the same USB sound card.

Here is the config file :

pcm.dmix8 {
    type dmix
    ipc_key 1001
    slave {
        pcm "hw:2"
        rate 44100
        channels 8
        period_size 1024
        buffer_size 32768
    } }

pcm.ch1 {
    type plug
    slave.pcm dmix8
    ttable.0.0 1 }

pcm.ch2 {
    type plug
    slave.pcm dmix8
    ttable.0.1 1 }

pcm.ch3 {
    type plug
    slave.pcm dmix8
    ttable.0.6 1 }

pcm.ch4 {
    type plug
    slave.pcm dmix8
    ttable.0.7 1 }

pcm.ch5 {
    type plug
    slave.pcm dmix8
    ttable.0.4 1 }

pcm.ch6 {
    type plug
    slave.pcm dmix8
    ttable.0.5 1 }

pcm.ch7 {
    type plug
    slave.pcm dmix8
    ttable.0.6 1 }

pcm.ch8 {
    type plug
    slave.pcm dmix8
    ttable.0.7 1 }

pcm.all {
    type plug
    slave.pcm dmix8
    ttable.0.0 1
    ttable.0.1 1
    ttable.0.2 1
    ttable.0.3 1
    ttable.0.4 1
    ttable.0.5 1
    ttable.0.6 1
    ttable.0.7 1 }

With this config file, everything works as expected !! The channel "all" is used by Asterisk as a local softphone, and ch1...ch8 are used to play different mono sounds in 8 different rooms. And when I call Asterisk, it auto-answers and I can hear the voice in the 8 HP, mixed with existing sound of the room :)

Thank you very much for your help !

Next step, try on my raspberry PI 3 board, but no reason to have a different behavior.