[pulseaudio-discuss] PulseAudio null sink monitor gives distorted audio randomly

Alexander E. Patrakov patrakov at gmail.com
Thu Nov 8 09:56:23 UTC 2018

Mikael Nousiainen <mikaelnousiainen at fastmail.com>:

> I've got a very weird issue with PulseAudio when trying to route audio
> from one application (Firefox 64.0b7 (64-bit)) to another one (WSJT-X v1.9.1).
> I'm experiencing the same issue with different browsers (Chrome and Chromium too).
> The browser is receiving audio from a radio transceiver through a WebRTC
> connection and I'm feeding it to WSJT-X to decode the data in the audio signal.
> I'm using two module-null-sink modules to transfer the audio between
> the browser and WSJT-X. I use pavucontrol to make the browser play audio to
> null sink called "radio-output" and then let WSJT-X listen to the audio
> via "radio-output.monitor". The kind of setup exists for transmitted audio
> where WSJT-X feeds audio to the browser through a null sink called "radio-input".
> However, the issue her is that WSJT-X is mostly not able to decode the data
> when it's using "radio-output.monitor" as audio input. Sometimes it works
> and sometimes it does not. As a technical detail, I'm trying to decode FT8
> digital mode traffic and I've confirmed that the reason is not related to
> bad time sync (which FT8 requires), because I can even play the browser
> audio through laptop speakers and let WSJT-X use the laptop microphone as
> audio input and it decodes the data just fine -- the audio sounds clean
> and strong with no audible artifacts.

We need to figure out whether this is due to a monitor or due to a
null sink. Could you please let the browser play to your speakers, and
WSJT-X record from the monitor of the sound card that the browser is
playing to? Does it work?

Is the webrtc feed public? I.e., can I run WSJT-X locally in order to
reproduce the issue?

Alexander E. Patrakov

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