Garmin GTN XI Series Manual page 51

Setup controls allow you to access:
Communication modes between pilot, co-pilot, and passenger
Distribution and mute options for two music interfaces
Distribution and volume of phone calls
Passengers cannot transmit over the active COM radio, even if equipped with a
PTT key.
Volume and squelch may be set separately for the pilot, co-pilot, and passenger
intercoms.
To set volume and squelch levels, tap Pilot VOL/SQ, Co-Pilot VOL/SQ, or
Passenger VOL/SQ.
Directional keys increase or decrease volume and squelch.
Tapping Auto Squelch allows the unit to set squelch level automatically.
The GMA 35 provides two music interfaces. Select Music 1 or Music 2 to set:
Who hears music
When to mute music
Music volume