Kathrein UFD 574/S - Manual (Page 25)

Sound Settings
25
Mute Function
Press

on the remote control. The sound is then muted. The same
icon is then displayed on the screen.
Press this key again. The sound is now unmuted again. To indicate
this, the volume bar is displayed for a few seconds.
You can change channel while the mute function is active, however,
this function is retained until the sound is either unmuted again or until
you re-adjust the volume with the corresponding keys on the remote
control.