[pulseaudio-discuss] Recording from USB devices without channel mixing

[Klaus Jaensch]

Hi Tanu,

Am 29.02.2016 um 15:13 schrieb Tanu Kaskinen:
> On Mon, 2016-02-29 at 14:23 +0100, Klaus Jaensch wrote:
>> Hello,
>>
>> we use USB audio devices (e.g. M-Audio Fast Track and Focusrite Scarlett
>> 2i2) to record mono speech on Ubuntu.
>> We face the problem that for mono recordings both input channels of the
>> devices are mixed together. But we want to record only the left channel,
>> not the mix. The left channel gets only half of the dynamic range; the
>> signal amplitude does not exceed -6dB.
>>
>> Is there a way to configure PulseAudio accordingly?
> If the recording program allows, you can specify its channel map to be
> "left" instead of "mono". For example, parecord supports the --channel-
> map option.
>
> If the recording program forces you to use "mono" channel map, you can
> use module-remap-source:
>
> pactl load-module module-remap-source sink_name=mono_source master=... channel_map=mono master_channel_map=left remix=no
>
> The "master" argument is the source name of the usb sound card. You can
> find the name with "pactl list sources". Once the remap source is
> loaded, you can point the recording program to "mono_source".

thanks, that works fine!
I need it system-wide for all users, therefore I put these lines:

load-module module-remap-source source_name=mono_source 
master=alsa_input.usb-M-Audio_Fast_Track-00-Track.iec958-stereo 
channel_map=mono master_channel_map=left remix=no
set-default-source mono_source

to /etc/pulse/default.pa

I'm wondering why it is the default to mix the channels.  I think mixing 
should be done by the applications, not by the audio system.

Klaus

> -- 
> Tanu

-- 
------------------------------------------
Klaus Jaensch
Muenchen
Germany

Institut fuer Phonetik und Sprachverarbeitung
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EMail: klausj at phonetik.uni-muenchen.de