Post by Paul Post by Dirk T. Verbeek
Had been using external mics and such with 16.04. All controlled
with Pulseaudio. Lately, I'm noticing a LOT of distortion when
trying to use my external mic. Didn't have this before the upgrade.
To describe the sound, I would say it sounds like if you were to
record audio at a very low sampling rate, play it back, and hear the
distortion. I tried switching out mics and get the same distortion.
No good for Zoom and others if that is present. Pulseaudio seemed
to upgrade to the current version, 11.1. Perhaps I need to
uninstall and reinstall a prior version, but not sure how. Any
thoughts would be welcome.
Have you tried adjusting the volume through pavucontrol?
Yes, I can adjust it there. I seem to have found a solution, or at
Particularly step 1B there where it says to reboot. Just killing
pulseaudio did not solve the distortion.
Of course, if I have to reboot each time to get rid of the distortion,
this is no good so still seeking a better solution.
You can use two computers, and have one send a sine wave to the other
The purpose of sending known-patterns, is to better understand the
type of distortion. Whether it's clipping, echo or reverb and so on.
I find a common occurrence in modern times, is the notion of
"monitor mode" and "echo suppression". Monitor mode is where some
recording input is played through the speakers. In the case of
a microphone, this would result in a feedback loop and you'd get
a squeal. But the audio subsystem can also be using an echo
suppressor. And this can do things like "hollow out" the sound.
These processing steps also tend to make a mess of Zoom or
Skype or whatever.
Sine waves are good for checking signal quality. 440Hz would do.
Trapezoidal pulse signals, "drawn" in Audacity, can be used
to check for echo or reverb or "processing" type filters. The
idea is, you want to see if the distortion you hear is some
"effect" that should not be there.
A typical example is a sound driver, where the control panel
says "effects = None", and yet, by driving pulses through the
sound system, you can see this. A situation like this can
"muddy" classical music, but for rock doesn't seem so bad.
+----+ Called "concert hall" effect
| | +----+
----+ +----- ~~ ------+ +-------
0 msec 30msec
Now, I tried to set up a demo here with Audacity, and I'm
embarrassed to report, I "couldn't find the signal" :-/
No amount of Poettering with my setup could find the
signal so I could record it. Am I an idiot or what ?
There were only about a dozen things in the menu, and
none of them had a signal on it the audacity monitor could find.
if you can get the notion to work, it would be fine I guess...
I know what happens to the audio when I hear it. I was initially using
Audacity to record the mic and then play back so I could hear what was
happening, then I found this command:
pactl load-module module-loopback
This will show up in the recording tab of pavucontrol. As I speak, I
can then hear myself and as long as the audio is low, I don't get
It seems to be, judging from what I am hearing, that my audio is being
resampled somehow to a much lower rate. It would be like playing an
audio file originally recorded at at a native 44.1 Khz back at say 4
Khz. The amount of ringing and distortion would be terrible.
For now, I have reset the "avoid-resampling = false" in the daemon.conf
file to "true" so that hopefully nothing is automatically resampled for
now on. I understand that there was/is a bug that ignores the change,
however, so I'm just hoping that the bug has been fixed by now.
Another thing I found was highest sampling rate of my sound card did not
match the default sampling rate of PulseAudio. The sound card is 48000
Hz and PulseAudio was set to 44100 Hz. I have since changed the
daemon.conf "default-sample-rate" to 48000.
If I still find failure, will try additional steps. I had no such
issues before the upgrade from 16.04.