Specifies how long the pattern should mute for, measured in 16th notes (irrespective of a pattern's BPM division setting!). If 'Mu.Ln' + 'UM.Ln' does not the equal pattern length (Pt.Ln), interesting polymeters can eventuate. Muting starts when the pattern starts playing, but this position can be offset by the 'Mu.Of' (mute offset parameter) to be later or earlier.