... Player controller and control digital display 2), MP3. in: Accepts signal from SD/MMC/MS Card and USB jack, supports MP3 ... the line in channel 7), Line in: Accepts line level signal from external music source, such as Mixer 8), Volume: Controls ... ), Clip led: Lights up when system signal level approaches clipping. 13), Line out: Sends a mixed signal of the unit at line level ...