Linux – Pipe/Mix Line In to Output in PulseAudio

audiolinuxpulseaudio

I work on two computers with one USB headset. I want to listen to both by piping the non-Linux computers' output into the Linux computer's line in (blue audio jack) and mixing the signal into the Linux computer's headset output using PulseAudio.

pavucontrol shows a "Built-in Audio Analog Stereo" Input Device which allows me to pick ports like "Line In" (selected), "Front Microphone", "Rear Microphone". I can see the device's volume meter reacting to audio playback on the non-Linux machine.

How do I make PulseAudio play that audio signal into my choice of Output Device?

Best Answer

1. Load the loopback module

pacmd load-module module-loopback latency_msec=5

creates a playback and a recording device.

2. Configure the devices in pavucontrol

In pavucontrol, in the Recording tab, set the "Loopback" device's from input device to the device which receives the line in signal.

In the Playback tab, set the "Loopback" device's on output device to the device through which you want to hear the line in signal.

3. Troubleshooting

If the audio signal has issues, remove the module with pacmd unload-module module-loopback and retry a higher latency_msec= value

This answer was made possible by this forum post. Thanks!

Related Solutions

Linux – How to load a module to PulseAudio server

To load a specific module to the PA server, you add it to /etc/pulse/default.pa:

load-module module-device-manager

Changes can also be made during runtime using pacmd.

Debian – How to enable both built-in audio output and HDMI audio output with PulseAudio

I just managed to configure exactly this thanks to the instructions in the ArchLinux wiki :

Set the one sink - HDMI - in pavucontrol/Configuration, and the other - analog output - you specify in default.pa :

load-module module-alsa-sink device=hw:0,0
load-module module-combine-sink sink_name=combined
set-default-sink combined

Maybe you were missing the last two lines?

Addendum: This is OK to add the analog output to HDMI, but what if you want it the other way around? (I want to keep analog input, Pulse calls that "duplex"...) Unfortunately, load-module module-alsa-sink device=hw:0,3 did not work to add HDMI output to Pulse's "Analog Stereo Duplex" configuration. Pulse would start, but no HDMI output.

I compared the output of pacmd list-sinks in the two situations. When I added device=hw:0,3, that one would show up without ports. When HDMI output was chosen in pavucontrol, there would be ports. Looking at the output details, I came up with device=hdmi:0.

Choose "Analog Stereo Duplex" as your pavucontrol configuration, and add to default.pa :

load-module module-alsa-sink device=hdmi:0
load-module module-combine-sink sink_name=combined
set-default-sink combined

Works like a charm. I keep my microphone input, and on pavucontrol/Output Devices I have all options for analog output and for HDMI.