[pulseaudio-discuss] No audio output; same setup worked before

[Sean Greenslade]

On Fri, Feb 12, 2021 at 12:14:00PM -0800, Rich Shepard wrote:
> Before getting the USB headsets working (thank you very much!) I used my
> AudioTechnica AT2500USB condenser microphone to record the audio portion of
> videos. Today I decided to again use it for recording and leave the headsets
> for online, virtual meetings. So I set up the AT again.
> 
> The AT mic is connected via XLR to a Focusrite Scarlett Solo pre-amp. The
> Focusrite is connected via USB to a front panel port on the desktop's case.

I'm a little confused by this description. As far as I know, the
ATR2500-USB only supports USB connection, not XLR. I'll assume you meant
you have a different XLR microphone plugged in to your Focusrite
interface.

> I configured pavucontrol so it sees the webcam and the AT mic as inputs; the
> audio device is seen as Scarlett Solo USB (rather than AudioTechnica
> AT2500USB) and the Input Devices tab shows that same device name with the vu
> meter responding to microphone input. A test file created with arecord shows
> the audio stream:
> $ ffprobe -hide_banner test-mic.wav Input #0, wav, from 'test-mic.wav':
>    Duration: 00:00:16.00, bitrate: 64 kb/s
>      Stream #0:0: Audio: pcm_u8 ([1][0][0][0] / 0x0001), 8000 Hz, 1 channels, u8, 64 kb/s
> 
> The Output Devices tab has only one device: HD Audio Generic Analog Stereo
> with the Port Line Out (Plugged In). The external speakers are turned on and
> I hear clicks when I adjust the volume on pavucontrol, but no sound when I
> play 'test-mic.wav' with aplay.
> 
> I've looked at pavucontrol tabs and don't see why I'm not hearing that audio
> stream.
> 
> What have I missed? Wrong arecord parameters?

I see you referencing "arecord" and "aplay", both of which are ALSA
utilities. While those should work (assuming you have the
pulseaudio-alsa package installed), they are a little harder to to make
behave nicely in Pulseaudio due to the limitations of the ALSA APIs that
Pulse has to emulate. I would suggest using the "parecord" and "paplay"
utilities, which are meant to directly interact with Pulse.

These utilities let you specify a recording or playback device directly,
or you can leave it unspecified and they should default to the fallback
device (as selected by the check marks in the Output Devices and Input
Devices tabs of Pavucontrol).

Note that you can check the recording source of a currently-recording
app in Pavucontrol just the same way you can check the playback sink of
a currently-playing app. So I would recommend checking the "Recording"
tab of Pavucontrol while recording to make sure that your app is indeed
recording from the source you want, and that the VU meter is showing
appropriate response.

You can also visually check the produced WAV file with an editor like
Audacity to be sure that the audio is making its way into the file.

--Sean