Sound consoles are designed to sound best at Unity Gain (Unity means ‘Zero’, or the number of dBs difference from where the console was designed to sound best) However, it is rare that input signals come in at the level needed for unity gain. In order to set the gain properly, we need to recognize what happens when the gain is too high or too low.
When the gain is turned up too high, we suffer from clipping, or distortion. There are two main problems with clipping. When a signal is clipped, we get an inaccurate reproduction of the sound wave (distortion). Also, the movement of the loudspeaker stops when the wave clips, which causes the speaker to expend energy as heat rather than movement, which will overheat the loudspeakers eventually.
When we have too little gain, we suffer from a lower signal to noise ratio. Every system has some noise (static/hiss/buzz). When the signal is large enough, (a.k.a when we have enough gain) the ratio is such that the noise is not noticeable. With a large signal, we won’t hear the background noise. This allows you to use your faders more effectively.
If the gain is turned up too high, we run into the problem of clipping. If the gain is too low, we have a lot of noise in the signal. Finding the sweet spot in the middle is the art of mixing sound.
So how do we go about doing this? There is often a button labeled Pad, Line, or Attenuator, which reduces the amplitude by 30dB. There is also often a knob or pot labeled gain, trim, level, input level, input, or input Attenuator. This adjustor allows one to adjust the amplitude of the audio coming into the console.
By pressing the PFL or Solo button, one can see the level of the signal coming into the mixer on the meters. PFL stands for “Pre Fade Listen” or “Pre Fade Level”. If the sound is to loud at Unity Gain, it is best practice to turn down the volume, or gain
at the last item in the signal chain, usually the power amplifiers.
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