The output from different microphones can vary greatly depending on their sensitivity and the sound pressure level they’re picking up.
That’s why it’s important to properly set the gain (or attenuation, if necessary) on the input to a microphone preamp, whether built into an audio console or a standalone unit.
On an audio console this control is often at the top of a channel strip, typically labeled “gain”, or something similar. Some consoles may provide a small LED meter or a peak indicator light.
For each microphone, set the input gain so that, for a typical input sound pressure level to the mic, you obtain your operating level. A pre-fader meter, if available, can be helpful in setting the correct level.
If you have too much gain for your microphone, you run the risk of overloading the input to the mic preamp, and causing distortion. The signal may be so hot that you’ll actually need to attenuate it before feeding it to the mic preamp. If your console doesn’t provide enough attenuation, use a mic attenuator inserted between the mic and the console input.
If your console or mic preamp has an overload indicator, keep an eye on it. If it lights infrequently and momentarily, you’re probably ok. But if it’s on fairly constantly, then back off on the gain setting. And of course, if you hear any distortion, check the input gain setting as part of your diagnostic routine.
If you have too little gain, you’ll end up adding noise to that mic channel as you try to bring up the channel, group, or master faders in an attempt to compensate for the low level.
If you have a mic with a particularly low sensitivity and a quiet talker, you will need to make sure that your audio console or mic preamp can provide enough gain to obtain operating level with low noise.
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