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Trim: Problems on the Front End


Do you hear distortion but none of your gain/volume controls is really high?


The problem could be gain on the input channel.

These controls are usually knobs at the top of the mixing board, one per channel labelled 'trim' or 'gain.'

So, how do you tell this is the problem?

The easiest way is to use the Pre-Fader Level monitor (PFL) button on the channel.

This button routes the signal before the fader (slider) to the output meters usually located above the master gain control.

This button is usually located either just above the fader (slider) or just below it on each channel (some mixers have additional PFL monitor points later in the signal chain, like submixes, monitor sends, and even master faders).

Many mixers have an LED light near the PFL button that blinks or lights when the PFL button is pressed.  Some mixers have another LED light near the master meters and master faders (sliders) that either lights or blinks when any individual channel's PFL button is pressed to let the operator know that the meter is not displaying its default value (the default value is usually to display the output of the mixer after the master fader [AFL] - this what the mixer is putting out to the power amplifiers).

Roll over a circled area to see details.




When the PFL button is pressed on the channel, adjust the trim/gain knob so that the signal never goes above the 0-db mark on the meter.  On multi-color master level meters, this is usually the highest green LED light (the next segment is usually yellow).


If you have headphones and can use them in the headphone jack on the board, the PFL button will also route the selected channel's audio signal to the headphones.  There is usually a knob to adjust headphone volume near the headphone jack.

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