Preamps and Gain

The preamp lifts a microphone's tiny voltage to line level. Gain staging sets noise floor and headroom.

Related

PreampGainHeadroomNoise Floor

The problem

A microphone delivers only a few millivolts; plugged straight into a converter, it gives almost nothing. The preamp raises that signal to line level. How much gain you add, and where, sets the noise floor, the headroom and the tone, not just the loudness.

Signal chain

Microphone → preamp → converter → workstation. A preamp usually offers 40 to 60 dB, sometimes with a pad and an impedance switch. Leave headroom in the analogue stage, and aim for peaks between -12 and -6 dBFS in the digital stage. Keep the analogue stage clean before asking the converter for more level.

Placement and settings

For a loud source, engage the pad first, then 48 V, then raise gain slowly. Set the peak from the loudest passage, not the quietest, and do not fix it with a fader. If you want more low-end weight, try distance and polar pattern before changing the preamp.

What to listen for

Raise gain from low to high and listen for hiss and room sound rising together. As clipping approaches, the low end usually blurs first. Compare the attack of the same phrase at two gain settings and hear whether it survives.

Common misconceptions

• Gain and volume are the same → gain lives in the analogue stage, the fader in the digital stage, and they affect noise differently.
• The meter must reach 0 → 0 dBFS is a ceiling, not a target.
• Preamp colour always sounds better → colour is a choice, not a guarantee.

Sources

• Ballou, Handbook for Sound Engineers, 5th ed., console gain and noise chapters
• AES recommended practice for professional audio, level and interconnection terminology

Used for fact-checking only; all prose is original.