On each track, a "Loudspeaker" icon is displayed 
. This icon represents the "Mute" function.
To mute a track :
•Click on the "loudspeaker" icon available on the track you want to mute.
A red cross is shown on the loudspeaker. The track is muted.
•To unmute it, click again on the "Louspeaker" icon 
. The track is unmute (the red cross disappears).