Add perceptual volume adjustment

The perceived loudness change of a change in volume depends
on the listening volume: at high volumes a 1 dB increment is
noticeable, but at low volumes a larger increment is needed
to get a comparable change in loudness.

Perceptual volume adjustment accounts for this fact, and
divides the hardware volume range into a number of steps.
Each step changes the dB volume by a variable amount, with
most of the steps concentrated at higher volumes. This
makes it possible to sweep over the entire hardware volume
range quickly, without losing the ability to finely adjust
the volume at normal listening levels.

Use "Volume Adjustment Mode" in the system settings menu
to select perceptual volume mode. The number of steps used
is controlled by "Number of Volume Steps". (Number of steps
has no effect in direct adjustment mode.)

It's still possible to set a specific dB volume level from
the sound settings menu when perceptual volume is enabled,
and perceptual volume does not affect the volume displayed
by themes.

Change-Id: I6f91fd3f7c5e2d323a914e47b5653033e92b4b3b

1 files changed, 2 insertions, 0 deletions

diff --git a/apps/plugins/sdl/SDL_mixer/timidity/playmidi.c b/apps/plugins/sdl/SDL_mixer/timidity/playmidi.c
index 1638732dc5..38f7109b13 100644
--- a/apps/plugins/sdl/SDL_mixer/timidity/playmidi.c
+++ b/apps/plugins/sdl/SDL_mixer/timidity/playmidi.c
@@ -21,6 +21,8 @@
 
 #include "tables.h"
 
+/* ROCKBOX HACK: avoid a conflict with adjust_volume() in misc.h */
+#define adjust_volume adjust_midi_volume
 
 static int opt_expression_curve = 2;
 static int opt_volume_curve = 2;