How to add an audio delay for video conferencing on Linux/Pulseaudio

After recently switching to work under Linux, I needed a way to replicate my existing solution for delaying audio under Windows under Linux/Pulseaudio.

To once again explain my situation, I use OBS also for video conferencing, through the virtual camera¹. OBS does not offer a built-in way to provide a virtual microphone with all the filters and such applied as well (in my case noise reduction and a limiter), so I need to solve this in a separate way. Additionally, my camera setup has a small delay of around 350ms that I also need to compensate by delaying my audio.

OBS offers a monitoring port that you can push your audio devices on, and that will get the filters applied, but none of the configured offsets. On Windows, I solved this by using a combination of two Virtual Cable devices and RadioDelay between the two.

Today I rebuild basically the same setup on Linux via a bunch of virtual Pulseaudio devices. I have this in ~/.local/bin/obs-virtual-mic:

#!/bin/bash

# create virtual speaker
pactl load-module module-null-sink sink_name=Virtual-Speaker sink_properties=device.description=Virtual-Speaker

# create delayed virtual speaker & associated mic
pactl load-module module-null-sink sink_name=Virtual-Speaker-Delayed sink_properties=device.description=Virtual-Speaker-Delayed
pactl load-module module-remap-source source_name=Remap-Source master=Virtual-Speaker-Delayed.monitor

# copy from virtual to delayed virtual with 350ms delay
pactl load-module module-loopback latency_msec=350 source=Virtual-Speaker.monitor sink=Virtual-Speaker-Delayed

Let’s take a closer look at what this does:

• create two virtual sinks Virtual-Speaker and Virtual-Speaker-Delayed with pactl load-module module-null-sink ...
• create a virtual source for the delayed sink via pactl load-module module-remap-source ...
• finally mirror the sound from Virtual-Speaker.monitor to Virtual-Speaker-Delayed while adding a latency of 350ms

I run this. Then OBS gets set to use Virtual-Speaker as monitor. In my video conferencing software I then use Virtual-Speaker-Delayed as my input to get my video and audio synced up.