On 02/19/2018 06:46 PM, Andreas Hartmetz wrote:
> Hello!
>
> I am currently developing an audio system for an automotive customer,
> based on PulseAudio where PulseAudio is applicable. It is part of the
> requirements that the volume of every input channel (sink input) to
> every output channel (sink) can be configured separately. There are
> good reasons for this, for example there can be two backseat info-
> tainment "terminals" which could send their audio to a headphone for
> each, or to the speakers in the whole car. The user-exposed volume
> controls will of course present a simplified vew, but for factory
> configuration, the described control is needed, and volume levels are
> expected to change at runtime in response to some external events.
>
> The problem is that PulseAudio does not support that. It could almost
> be "hacked" by using one module-combine-sink for every sink input,
> which at least allows sending a stream to an arbitrary collection of
> sinks. But it does not support volume control at all.
>
> So:
> - Is there a way that I didn't think of to piece together the
> desired volume control using existing modules and/or other
> configuration? I don't want to resort to anything really weird
> like creating lots of "loopback" devices using local sockets or
> something like that (also for latency reasons), and running
> multiple server instances also won't do it due to PA requiring to
> open devices exclusively. Also, any hacky solution is not allowed
> to significantly increase (or worse, hide from PA so it can't be
> compensated) latency.
> - If not, what do you think would be the best way to do it? I'm
> thinking of a potential "module-crossbar" that I would need to
> write, which allows matrix-style (n, m) volume control, i.e.
> set_volume(sink_input_index, sink_index, volume).
>
Volume for each sink-input can configured separately:
$ pactl list sink-inputs
Sink Input #0
Driver: module-loopback.c
Owner Module: 4
Client: n/a
Sink: 0
Sample Specification: s16le 2ch 96000Hz
Channel Map: front-left,front-right
Format: pcm, format.sample_format = "\"s16le\"" format.rate = "96000" format.channels = "2" format.channel_map = "\"front-left,front-right\""
Corked: no
Mute: no
Volume: front-left: 65536 / 100% / 0.00 dB, front-right: 65536 / 100% / 0.00 dB
balance 0.00
Buffer Latency: 133657 usec
Sink Latency: 56936 usec
Resample method: trivial
Properties:
media.role = "abstract"
media.name = "Loopback from Null Input"
media.icon_name = "audio-input-microphone"
$ pactl set-sink-input-volume 0 32768
$ pactl list sink-inputs
Sink Input #0
Driver: module-loopback.c
Owner Module: 4
Client: n/a
Sink: 0
Sample Specification: s16le 2ch 96000Hz
Channel Map: front-left,front-right
Format: pcm, format.sample_format = "\"s16le\"" format.rate = "96000" format.channels = "2" format.channel_map = "\"front-left,front-right\""
Corked: no
Mute: no
Volume: front-left: 32768 / 50% / -18.06 dB, front-right: 32768 / 50% / -18.06 dB
balance 0.00
Buffer Latency: 133593 usec
Sink Latency: 20936 usec
Resample method: trivial
Properties:
media.role = "abstract"
media.name = "Loopback from Null Input"
media.icon_name = "audio-input-microphone"
> Thanks in advance!
>
> Andreas Hartmetz
>
>
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>
--
Raman
