Videolan is a really popular Open Source multimedia player. In it’s most recent versions, the interface has been redesigned with the Qt Toolkit and introduces a new audio volume control.
This control now provides the ability of amplifying sound, which is more than just setting up output levels. It ranges from 0% up to 200% (+3dB). While this might be really useful for some DVD or bad audio tracks, this initial design brings many problems.
VLC volume control with built-in amplification
Users can’t set precisely the volume to 100% without applying amplification.
The 100% level is not materialized in any way in the control and the user has the only option to slide volume approximately until it reaches 100%. Aiming at the right level is difficult and going too far triggers amplification.
Volume control’s shape doesn’t provide efficient visual feedback.
The triangle shape gives wrong feedback at extreme values, especially because the control ranges up to 200%. For example, a 50% level which should appear like a quarter of the shape seems really less because of the covered surface difference.
Volume level use colors depending on arbitrary values
As commonly seen on many mixers controls,the increasing audio level goes from green to red. This is inspired from Vu-Meters and in most of the cases wrong.
Vu Meter
Traditionals Vu-Meters have a red zone working in combination with a gain button which works in addition to the regular volume level. The reason is that not every soundtrack have the same peak and average audio signal levels. Gain is used to “align” to the upper bound and so “maximizing” the amplitude of those signals. When post-processed it is called “normalizing”. A sound signal using the maximum allowed amplitude gets optimal dynamics.
Audio level graph. Audio signal does not use full amplitude
Normalized audio, max peaks reaches the upper level
On recent hardware mixer tables those Vu-Meters are usually replaced with Led Vu-Meters, adding some yellow zone around -3dBa amplification and green for eveything under. This seems the inspiration of this widget.
But you can notice that colors are static and then: 0% is green, volume at 100% is orange and amplified volume is red. While you might not see the problem, this is obviously wrong. Red on Vu-Meters means that the sound peaks are too high: it’s saturated. Those feedback colors can’t be set statically as each audio track has it’s own signal.
+8db amplified audio. Here most of the peaks are "cut"
+20db saturated audio. The whole signal saturates and results in the worst audio quality.
A short and expressive example: Take an audio track with just silence, play it at 200% output (with 2x amplification), you can guess that a 0 will still result in a 0 and won’t get any more amplitude. While this widget would show a “red” saturating level.
Muting audio hides values
When audio is muted, the level switchs to 0%. Unmuting will result in restoring an unknown value. Hope that you don’t mute to take a long phone call in the evening and restore it late at night in the middle of gunfight scene 
Duplicate level feedback from icon’s waves and slider shape.
The speaker icon next to the volume shape has waves dynamically drawn according to the current level. This is duplicate audio level.
Widget redesign clues
sample sliders
First sketches aims at drawing a control providing volume level reference and dynamic amplification feedback.
Refining those ones, the next step is to get rid of the triangle shape to a rectangular one and relocating the amplification ability as an option.
The last sketches is a thought about a two axis control with dynamic signal visualization.
