Public bug reported:
Hello, I have a mono microphone which plugs to the rear stereo jack of my ASUS
P5K motherboard (the leftright poles of the microphone are in short circuit).
It works perfectly on Windows (the waveform baseline is not shifted) and even
on different computers.
Whenever I change the microphone volume while I'm recording on audacity the
waveform amplifies and that's ok, but also the baseline of the waveform shifts.
If I raise the microphone volume:
- the left channel waveform shifts down (towards negative dB);
- the right channel waveform shifts up (towards positive dB);
- the amplitude of both waveforms enlarges.
Raising too much the microphone volume will eventually make both channels peak,
therefore recording only silence.
Changing the input channels of audacity to 1 (mono) doesn't shift the
waveform, but it peaks the same way as it would on stereo resulting in
silence at 100% of microphone volume.
In this page there are a couple of tests I've made if my words weren't clear
enough:
https://drive.google.com/folderview?id=0B2nNWg6orzuceVc4dVNuUjFsbWMusp=sharing
The alsamixer.mp4 video shows how the DC offset of the single channels changes
together with the input's volume.
The pavucontrol-*.mp4 shows the same thing but changing the volume from
pavucontrol.
The pavucontrol-mono.mp4 shows how recording on mono makes the input peak
anyways after some threshold of volume.
In the videos I play music and record at the same time, the microphone gets the
sound from my speakers, audio file .wav of the record is provided as well.
Two screenshots of the sound preference windows are provided.
My OS is Linux Mint 16 (MATE edition) - amd64.
(Yes, it's Linux Mint 16, but it's based on Ubuntu Saucy Salamander 13.10)
I installed the
oem-audio-hda-daily-dkms_0.201405282018~ubuntu13.10.1_all.deb, released 18
hours ago, and the problem remains.
Dario Rubiano
** Affects: linux (Ubuntu)
Importance: Undecided
Status: Incomplete
** Tags: alsa dc input microphone offset saucy shifted volume waveform
** Attachment added: alsa-info before of the installation of
oem-audio-hda-daily-dkms_0.201405282018~ubuntu13.10.1_all.deb
https://bugs.launchpad.net/bugs/1324588/+attachment/4122307/+files/alsa-info.txt.wnKI3h6S6f
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https://bugs.launchpad.net/bugs/1324588
Title:
Microphone input DC offset of stereo channels proportional to volume
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