• Button-type digital adjustable Volume (0dB/-3Db/-5 dB/-10 dB/-15 dB/OFF ); Base(+6dB/+2 dB/0dB/-2dB-6dB); Treble(+6 dB/+2 dB/0 dB/-2dB/-6dB). • Four conference modes: FIFO (first-in first-out mode); NORMAL (normal mode); FREE (free mode);APPLY (apply speaking). * Function to limit the number of spokesman: adjustable speech unitsnumber: 1, 2, 4, 6; chairman unit is not restricted by it.