[Bug 416190] Re: Pulseaudio produces overdriven audio on mono downmix (e g to Plantronics DA40 adapter)

[David Henningsson]

** Description changed:

- In Intrepid and Jaunty, audio sent through the Plantronics DA40 is
- distorted if the per-application volume is above around 80%.
- Unfortunately, all applications default to 100%.  Audio sent directly to
- the ALSA device is not distorted, so this is something happening in
- pulseaudio.  I attempted to test this under Karmic, but the volume
- sliders behave very differently, with the pavucontrol sliders adjusting
- the ALSA "Speaker" mixer, and I was unable to remove the distortion at
- all.
+ [SRU Justification]
+ Impact: See below. But in short, distorted sound when on an analog-mono profile. Most soundcards support analog-stereo only, but for some hardware, this is a problem.
+ 
+ Testcase: Using hardware that supports analog-mono profile, play back audio, source
+ material at sufficient volume. If this bug is fixed, there is no distortion.
+ 
+ Regression potential: Can't think of any, and if so, it should only
+ affect downmixing to mono, which is unusual anyway.
+ 
+ 
+ In Intrepid and Jaunty, audio sent through the Plantronics DA40 is distorted if the per-application volume is above around 80%.  Unfortunately, all applications default to 100%.  Audio sent directly to the ALSA device is not distorted, so this is something happening in pulseaudio.  I attempted to test this under Karmic, but the volume sliders behave very differently, with the pavucontrol sliders adjusting the ALSA "Speaker" mixer, and I was unable to remove the distortion at all.
  
  The DA40 is a mono device, so perhaps it's a problem with pulse
  downmixing stereo audio to mono without reducing the per-channel level,
  resulting in clipping.  but I tested with a DA45, which is a similar
  mono adapter, and the problem didn't exist.

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https://bugs.launchpad.net/bugs/416190

Title:
  Pulseaudio produces overdriven audio on mono downmix (e g to
  Plantronics DA40 adapter)

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