Gain

Gain is a change in signal level and can be applied anywhere in the audio chain, not only at its input. Input gain raises a microphone's or instrument's small signal to a useful recording level. A track fader or output-volume knob also changes level, but later in the chain. The practical distinction is where the control acts: lowering an output fader cannot undo clipping that already happened at the input.

Clipping and headroom

Every recording stage has a usable level range. In fixed-point digital audio, 0 dBFS (decibels relative to full scale) is the maximum representable sample level. Overloading an analog input or converter can cut off the waveform's peaks, causing clipping. Lowering the level afterward cannot reliably restore the lost waveform. Floating-point audio can hold values above 0 dBFS inside software without necessarily clipping, but those values must be reduced before an output stage or fixed-point export that cannot handle them. Headroom is the margin between your peaks and a stage's usable ceiling.

Too little gain has the opposite problem: the signal sits close to the background noise of the equipment, and turning it up later raises the noise as well.

Setting input gain

1. Ask the performer to play or sing the loudest passage they will perform, not a gentle warm-up.
2. Raise the gain on the audio interface or preamp until the meter shows healthy peaks.
3. Leave plenty of headroom. When recording at 24-bit, the loudest peaks can sit well below 0 dBFS with no audible noise penalty (sample rate and bit depth).
4. If the clip indicator lights, turn the gain down and record again. Lowering the fader afterward doesn't help, because the fader comes after the clipping.

Gain staging

Gain staging means keeping a sensible level at every step of the chain: the input, each plug-in, each track, each bus and the final output. If a plug-in boosts the level, turn its output down to match; then each process can be judged fairly and nothing overloads further along. Healthy, moderate levels throughout make mixing easier than loud tracks with every fader pulled down.

Gain on guitar amplifiers

On a guitar amplifier, the gain knob also sets how hard the preamp is driven. Turned up, it pushes the amp into distortion on purpose, while the master volume sets the overall loudness. It is the same idea with a different musical goal.

Gain is measured in decibels and acts on the amplitude of the signal.