TC Helicon Critical MassCRITICAL MASS Studio Quality Vocal Stompbox for Large Group Sound Effects A simple to use vocal stompbox lets you easily create stunning group sound vocal effects Powerful melodic and gang styles give you large group vocals using your voice alone No key or scale to set just sing Simple three knob control gets you up and running in seconds High quality, low noise mic preamp for pristine vocals On off foot switch for quick performance control Rugged,