JBL AV1 - Manual (Page 95)

AV1
Audio Controls
4-3
BASS Parameter Settings TREBLE Parameter Settings
The BASS parameter controls the amount of low-frequency boost or cut applied
to the audio output connectors labeled Front L/R, Center and Subwoofer.
The TREBLE parameter controls the amount of boost or cut applied to the
audio output connectors labeled Front L/R and Center.