Decibels and gain
On a fader, 0 dB leaves the level unchanged. Gain is the knob before the compressor and EQ. The fader is the level after them.
On a fader or a device output, 0 dB leaves the incoming level unchanged. Positive values boost it. Negative values turn it down. Channel gain goes as far as −∞, which is silence.
Gain is the first knob on a mixer channel, before the filter, compressor, and EQ. It runs from silence to +18 dB. Use it to set how hard the signal hits that processing. The fader at the bottom is the level after it. Leave the master fader at 0 dB and balance the song with the channel faders.
A drop of 6 dB is the same reduction at any point on the scale. From 0 to −6 matches −6 to −12. A knob marked in percent is a different scale: it sets dry/wet, the balance between a sound and an effect.