class GainControl

Enables control and monitoring of audio gain. This interface is typically a

tear-off of other interfaces.

## Knobs

This interface exposes two orthogonal knobs:

* The *gain* knob controls a single value in "relative decibels". A value of

0 applies no gain, positive values increase gain, and negative values

decrease gain. Depending on context, gain may be applied relative to an

input stream or relative to some absolute reference point, such as the

maximum loudness of a speaker.

This knob has no defined maximum or minimum value. Individual

implementations may clamp to an implementation-defined maximum value or

treat all values below an implementation-defined minimum value equivalent

to "muted", but this behavior is not required.

* The *mute* knob controls a single boolean value. When `true`, the

GainControl is muted and the effective gain is negative infinity. When

`false`, gain is controlled by the *gain* knob.

## Scheduling

Changes to the *gain* and *mute* knobs can be scheduled for a time in the

future. Scheduling happens on timestamps relative to a reference clock which

must be established when this protocol is created.