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Gain control

A post by David Mellor
Friday May 23, 2003
A description of the technology and function of the gain control as found in mixing consoles.
Gain control

The mic preamp (preamplifer) is where the input signal is conditioned so that it is suitable for further processing in the console.

Each channel of the console has two input sockets; mic input and line input.

The mic input can accept the output of a microphone (naturally) or a DI (direct inject) box. Nothing else should be connected to a mic input.

Anything else will be connected to the line input.

A microphone has a low output level. A typical figure would be 10 mV (one hundredth of a volt). The console likes to work on a signal level of around one volt to keep well above the inevitable noise signals that will be present.

This means that the signal has to be boosted by 100 times, or 40 dB (40 decibels).

Of course, the level that comes from the microphone depends on the level of the sound source, and its distance. In practice a mic preamp needs a range of gain of 20 dB up to 60 dB. Some preamps go beyond this range, from 0 dB to 80 dB. 0 dB means x1 or unity gain - in other words no gain at all. 80 dB means x10,000. This would cover all situations from a mic being placed 10 mm from the point where the kick drum pedal hits, to a watch ticking at twenty paces.

There would be no advantage in providing more than 80 dB of gain because the noise produced by the mic would be amplified above the console's noise level.

A post by David Mellor
Friday May 23, 2003 ARCHIVE
David Mellor has been creating music and recording in professional and home studios for more than 30 years. This website is all about learning how to improve and have more fun with music and recording. If you enjoy creating music and recording it, then you're definitely in the right place :-)
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