this knob sets how much of the source signal is sent to the rest of the mixer.too high and the signal will distort as it overloads the channel (shown by illumination of the peak led),and causes clipping.too low,and the level of any background hiss will be more noticeable and you may not be able to get enough signal level to the output of the mixer.set the knob fully anticlockwise as a preliminary position for line level sources.an individual channel meter monitors the input level at the lnsert point,making it easy to spot input overload.