[pulseaudio-discuss] pacmd shows wrong sample spec for USB mic? (high-pitched, sped-up input)

Georg Chini georg at chini.tk
Fri Mar 1 19:24:54 UTC 2019

Hi Ryan,

On 01.03.19 18:03, Ryan Lue wrote:
>> I’ve got a USB webcam mic that’s not playing well with PulseAudio:
>> recordings are high-pitched and sped up (like an Alvin and the Chipmunks album).
>> If I manually set PulseAudio’s default sample rate to 16000Hz
>> (via `/etc/pulse/daemon.conf`), then it sounds _perfect,_
>> but then the sound out of my bluetooth headset (44100kHz) is severely degraded.
>> I really don’t know much about how PulseAudio works,
>> but it appears that pacmd is reporting the wrong sample spec on the mic,
>> and I imagine that’s why it’s not working right:
>>      $ pacmd list-sources
>>      3 source(s) available.
>>        * index: 0
>>              ...
>>              sample spec: s16le 1ch 48000Hz
>>              ...
>> At first, I was looking for a way to manually set different sample rates
>> on different sinks/sources, but after a lot of failed Googling,
>> I’m beginning to suspect it doesn’t work that way?
>> So, is it possible to override the sample spec for a given sink/source?

No, this is not possible. PA uses either default-sample-rate or
alternate-sample-rate if the device supports one of the rates.
In your case I suspect that this is rather an ALSA bug and not
PA's fault. It looks as if ALSA falsely reports that your web cam
supports 48000 Hz, therefore PA will try to use that rate.

You could try setting default-sample-rate to 44100 and
alternate-sampling-rate to 16000 to work around the issue
and/or you can report a bug to ALSA.

> If this is the wrong place to ask about this, could anyone suggest a
> better one?

The mailing list is still the right place to ask questions. Alternatively
you can open an issue on gitlab:


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