D9726: Change device "master volume" to be the max of all channels instead of the avg

[Chris Holland]

Zren added a comment.


  > one channel is 0%, second is 100% and merged volume now shows 100%
  
  If you lower the volume on a speaker, you care more about what the volume of the louder speaker is. It's weird if the OSD shows 50% when the right speaker is blaring at 100% and annoying my neighbours. You'd need to do mental math that the right speaker is +50% (or whatever it is).
  
  -----
  
  Most OSes usually have a master channel slider, and a second slider for the left/right balance.
  
  1. KMix apperently used avg in the OSD I believe (I should probably install it and confirm). When the channels were split, it would have 2 sliders (and hide the "master") I think.
    - Source
      - https://github.com/KDE/kmix/blob/29ff33adc9a714dad29351e3dbbc3d4f474d4364/gui/osdwidget.cpp#L107
      - https://github.com/KDE/kmix/blob/29ff33adc9a714dad29351e3dbbc3d4f474d4364/core/volume.cpp#L314
    - KMix also had a feature request for turning it into a "Left <-> Right" channel balance slider. https://bugs.kde.org/show_bug.cgi?id=263105
  
  2. Windows 10 uses the max (https://www.youtube.com/watch?v=_9Zx4QMucx4#t=1m03)
    - Window's Realtek driver controller uses a "Left <-> Right" channel balance slider (https://www.google.ca/search?q=realtek+audio&tbm=isch).
  3. Can't find an OS X example. I think it uses a "Left <-> Right" channel balance slider (https://www.youtube.com/watch?v=UZxhBio-_18), but you can also edit the individual sliders too I think somehow.
  4. Mate (Gnome 2?) uses master volume slider + a "Left <-> Right" channel balance slider. F5630840: 2018-01-08___20-33-19.png <https://phabricator.kde.org/F5630840>
  5. Gnome 3 ?
  6. Unity?
  
  -----
  
  Correct me if I'm wrong, but I believe a "Left <-> Right" channel balance slider means at least 1 channel is always at a 100% ratio of the master volume. Since the center means both speakers are at 100%.
  
  F5630834: 2018-01-08___19-29-09-edit.png <https://phabricator.kde.org/F5630834>
  
  - `=========O=========` LeftRatio = 100% / RightRatio = 100%
  - `O==================` LeftRatio = 100% / RightRatio = 0%
  - `==================O` LeftRatio = 0% / RightRatio = 100%
  - `==============O====` LeftRatio = 50% / RightRatio = 100%
  - `====O==============` LeftRatio = 100% / RightRatio = 50%
  
  This means the "master volume" represents the "max" of all the channels.

REPOSITORY
  R115 Plasma Audio Volume Applet

REVISION DETAIL
  https://phabricator.kde.org/D9726

To: Zren, #plasma
Cc: drosca, plasma-devel, ZrenBot, progwolff, lesliezhai, ali-mohamed, jensreuterberg, abetts, sebas, apol, mart
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