Set the speaker's treble.

def treble(self, treble):
        """Set the speaker's treble."""
        treble = int(treble)
        treble = max(-10, min(treble, 10))  # Coerce in range
        self.renderingControl.SetTreble([
            ('InstanceID', 0),
            ('DesiredTreble', treble)
        ])