[pulseaudio-discuss] Why I can't find multichannel-input and multichannel-output paths in path folder

[Tanu Kaskinen]

On Wed, 2020-10-28 at 09:59 +0800, Chengyi Zhao wrote:
> Hi guys,
> 
> I have a computer with using Realtek ALC662 rev3,  it can adapt the 
> multichannel profile below,
> 
> but I can't find multichannel-input and multichannel-output paths in 
> path folder
> 
> (/usr/share/pulseaudio/alsa-mixer/paths), please tell me the working 
> logic of
> 
> multi-channel profile, and how it differs from other profiles, thanks!
> 
> ------------------------------------------------
> 
> [Mapping multichannel-output]
> device-strings = hw:%f
> channel-map = left,right,rear-left,rear-right
> exact-channels = false
> fallback = yes
> priority = 1
> direction = output
> paths-output = multichannel-output
> 
> [Mapping multichannel-input]
> device-strings = hw:%f
> channel-map = left,right,rear-left,rear-right
> exact-channels = false
> fallback = yes
> priority = 1
> direction = input
> paths-input = multichannel-input
> 
> ------------------------------------------------

The profile-set configuration indeed references non-existent paths. The
"paths-output" and "paths-input" options should be removed from these
mappings.

The multichannel mappings are tried when nothing else works (hence
"fallback = yes"), and the purpose of these mappings is to have some
kind of support for sound cards that can only be opened with 4 channels
or more, and don't define the standard "surround" alsa device names.
The "exact-channels = false" option means that if the sound card
requires using more than 4 channels, PulseAudio will open the device
with as many channels as necessary, but will only use the first 4
channels as defined with the "channel-map" option. The rest of the
channels get assigned "aux" positions, which are not routed to unless
an application uses the aux channels its own channel map (which
virtually no application does).

-- 
Tanu

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