Extraido del manual de la Soundcraft LX7:
4 - GAIN
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. 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.
See `Setting Up & Troubleshooting’ on page 20 to learn how to set GAIN correctly.
En esa sección leemos:
Set up individual input channel as follows:
Connect your sources (microphone, keyboard etc.) to the required inputs and release the MUTE switches. Note: Phantom
powered mics should be connected before the 48V is switched on.
Set Master faders at 0, input faders at 0, route the channels to MIX and set power amplifier level to suit the application.
Provide a typical performance level signal and press the PFL button on the first channel, monitoring the level on the
bargraph meters.
Adjust the input gain until the meter display is in the amber section, with occasional peaks to the first red LED at a typical
maximum source level. This allows sufficient headroom to accommodate peaks and establishes the maximum level for
normal operation (but see note below).
Repeat this procedure on other channels as required
Según el manual de la Allen & Healt GL2400
Important note on setting channel levels: Use PFL to set the GAIN
controls for correct signal level through each channel. The main LR
meters provide a high resolution display of the channel signal level.
Use the faders to balance each signal in the mix. To ensure optimum
gain structure we
do not recommend the practice of setting the faders
to ‘0’ and mixing using the GAIN controls (el subrayado en "we do not" no es mío. Está en el manual(página 16)
http://www.glseries.com/Downloads/gl2400ug_ap5597_2.pdf
Y se pueden ver los manuales de otras mesas. Suelen decir lo mismo.
Las razones no son académicas. Son técnicas.
El motivo siempre es el mismo: evitar distorsión y/o ruido. Hacer trabajar los circuitos en los márgenes de tensiones y corrientes para los cuales fueron calculados.
Ahora bien. Si te compras una mesa y la pagas, puedes (¡faltaría mas!) mezclar como te apetezca. Pero la mejor calidad de sonido la conseguiras de esa manera. Dejando entre el ajuste y el 0 dB solo el margen necesario (headroom) para prevenir picos inesperados.