[alsa-devel] Bug in alsa-lib or alsamixer and amixer
gmane at colin.guthr.ie
Wed Jun 16 01:07:52 CEST 2010
'Twas brillig, and Raymond Yau at 15/06/10 23:29 did gyre and gimble:
> 2010/6/16 Colin Guthrie <gmane at colin.guthr.ie>
>> 'Twas brillig, and Raymond Yau at 15/06/10 00:43 did gyre and gimble:
>>> +12dB(400%) is even larger than the software gain 150% of PA
>> Software gain of PA 150% = ~+11dB, so not as different as you imply.
>> I've explained the cubic mapping already, so please don't use arbitrary,
>> differently calculated percentages when comparing things. It's like
>> comparing apples to oranges.
> When I changed the volume slider of the gnome sound applet ( select
> perference ) in Fedora 13 to maximum (i.e. PA 150% )
> Seem to be bug in amixer and alsamixer
> alsamixer also change to 150% but press any key change back to 100%
The fact that any key changes it back to 100% is kinda expected. It's
not designed to handle values >100% so it makes sense that it clamps it.
Annoying, but it makes sense.
> The volume range is only from 0 to 65536
> why did alsa-lib allow alsa-pulse plugin to set it outside the range ,
> alsamixer and amixer also display 150% ?
> amixer -D pulse
> Simple mixer control 'Master',0
> Capabilities: pvolume pswitch pswitch-joined
> Playback channels: Front Left - Front Right
> Limits: Playback 0 - 65536
> Front Left: Playback 98304 [150%] [on]
> Front Right: Playback 98304 [150%] [on]
While I agree this could be thought of as a bug, it's actually the
nicest possible display for a system that has no concept of volumes > 100%.
That said, the correct fix would be a nice mechanism for marking the
100% mark. e.g. specifying the limits as a triplet, lower, normal (aka
100%) and max.
AFAIK, no such system is currently in place.
An alternative would be to scale the alsa volume control to the full
range, e.g. make 0 - 98304 the range it accepts. But this sucks as
the percentage shown in alsa is not the same as the percentage shown in
In a practical sense, the current setup is probably less problematic
than the latter suggestion.
 FWIW, this precice value will likely change. I've not yet actioned
it but it's likely to be fixed at +11dB which IIRC is slightly above
150%. 11dB is just a figure that we felt was "sensible" with regards to
GUI consistency and I'll try and push this out ot all the UIs I can.
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