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[Dario Rubiano <dario.rubiano@xxxxxxx>]

Public bug reported:

Hello, I have a mono microphone which plugs to the rear stereo jack of my ASUS P5K motherboard (the left&right 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=0B2nNWg6orzuceVc4dVNuUjFsbWM&usp=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

Status in “linux” package in Ubuntu:
  Incomplete

Bug description:
  Hello, I have a mono microphone which plugs to the rear stereo jack of my ASUS P5K motherboard (the left&right 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=0B2nNWg6orzuceVc4dVNuUjFsbWM&usp=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

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