Home Recording Mixer Basics: Trim Control
The Trim control is a knob that’s used to adjust the level of the input signal as it enters the home recording sound mixer. You usually find the Trim control at the top of the front panel of your hardware unit.
On SIAB systems and analog and digital mixers, this control is generally located at the top of the mixer section for each channel, and on audio interfaces, it’s often found on the front panel.
The amount that you adjust the Trim control depends on the instrument that you have plugged into the channel strip. If the Trim control is set too high, you get distortion; if it’s set too low, you get a signal that’s too weak to record. So be sure to listen as you make your adjustments.
Most Trim controls have a switch or markings for Line or Mic(rophone) signals, with the Line level to the right and the Mic level to the left. Turn the knob all the way to the left for line sources — or slowly turn it to the right for microphone sources — until you get a nice, clean sound coming into the mixer.
For microphone sources, you use the Trim control to adjust the level for recording. Turning the control up (turning the knob clockwise) activates an internal preamp in the mixer, which boosts the level of the signal coming from the mic.
The internal preamp in pro mixers is usually fairly decent (it can sound pretty good). However, many professionals prefer to use an external preamp because it can often sound better or have a sound characteristic they want.
If you use an external preamp, check the owner’s manual of your mixer to see whether you can bypass the internal preamp. Most professional mixers enable you to do this. Sometimes just turning the Trim control all the way down (to the Line marking) disengages the preamp from the circuit.