See also:

MUTE button (if equipped)
Press this button if you wish to immediately cut the volume to zero. The audio display will show “MUTE”. If you press the button again, the original sound volume will return and “MUTE” turns off. ...

Dimensions
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Other settings (type A, B and C audio)
Each brief press of the “MENU” button changes the control modes in the following sequence. Type A audio: Type B audio: Type C audio: Choose the preferred settings for each mode by tu ...