alsa-project/alsa-lib issue #273 was opened from anthonio9:

My goal is to mix the output of two sound cards (RAVENNA from [bondagit](https://github.com/bondagit/aes67-linux-daemon.git) and hifiberry), then pass it to a DSP pcm plugin. As it's not possible with `dmix` (dmix only supports output to hw devices) the reasonable next step was `multi` plugin, but my tries always end up in a failure. Below is a quite standard `multi` configuration inspired by alsa docs that I'm using:

```sh pcm.quad { type multi slaves.a.pcm "hw:RAVENNA" slaves.a.channels 2 slaves.b.pcm "hw:sndrpihifiberry" slaves.b.channels 2

bindings.0.slave a bindings.0.channel 0 bindings.1.slave a bindings.1.channel 1 bindings.2.slave b bindings.2.channel 0 bindings.3.slave b bindings.3.channel 1 master 1 }

pcm.quad2 { type plug slave.pcm "quad" } ```

This is run with `alsaloop` to be input into an extplug plugin that easily accepts 4 channels of audio - `alsadsp`: ```sh $ alsaloop -C quad -P alsadsp -c 4 Rate 48000Hz not available for capture quad: Invalid argument Unable to set parameters for capture quad stream: Invalid argument Loopback start failure. ``` This results in a failure, moreover running `quad2` also results in the same type of error.

Next step was to try plug pcm:

```sh pcm.quad_plug { type multi slaves.a.pcm "plughw:RAVENNA" slaves.a.channels 2 slaves.b.pcm "plughw:sndrpihifiberry" slaves.b.channels 2

bindings.0.slave a bindings.0.channel 0 bindings.1.slave a bindings.1.channel 1 bindings.2.slave a bindings.2.channel 0 bindings.3.slave a bindings.3.channel 1 }

pcm.quad_plug2 { type plug slave.pcm "quad_plug" } ``` With `quad_plug` the same error occurs, with `quad_plug2` the error is as below:

```sh $ alsaloop -C quad_plug2 -P alsadsp -c 4 Broken configuration for capture quad_plug2 PCM: no configurations available: Invalid argument Unable to set parameters for capture quad_plug2 stream: Invalid argument Loopback start failure. ``` Then the last thing I tried was to force the 48kHz sampling rate directly on the hardware devices with the help of the following config:

```sh pcm.quad_48k { type multi slaves.a { pcm { type plug slave.pcm "hw:RAVENNA" slave.rate 48000 } channels 2 }

slaves.b { pcm { type plug slave.pcm "hw:sndrpihifiberry" slave.rate 48000 } channels 2 }

bindings.0.slave a bindings.0.channel 0 bindings.1.slave a bindings.1.channel 1 bindings.2.slave b bindings.2.channel 0 bindings.3.slave b bindings.3.channel 1 } ``` and again it ends up with a failure:

```sh $ alsaloop -C quad_48k -P alsadsp -c 4 Sample format not available for capture quad_48k: Invalid argument Unable to set parameters for capture quad_48k stream: Invalid argument Loopback start failure. ```

I know that both these cards are capable of running 48kHz, I'm doing that all the time. So what could be the cause of this error? `alsadsp` wants them to be 48kHz and if run separately it all works well, both cards set themselves according to `alsadsp` requirements. It works even if there's only one card in the multi plugin that occupies all 4 output ports - my conclusion is that it's not a problem of `alsadsp`. Are there any other steps that could help solving the issue?

Issue URL : https://github.com/alsa-project/alsa-lib/issues/273 Repository URL: https://github.com/alsa-project/alsa-lib