Your preamp may have a VU meter, too, which is helpful to get you in the right ballpark. So much for theory! In practice, it’s best to just rely on the level meter in your recording software (DAW). So there are three variables: the loudness of the sound source, the microphone distance, and the microphone sensitivity. Condenser microphones usually have a very healthy output level, whereas dynamic mics, including ribbons, typically require much more gain due to their low sensitivity. And of course the microphone sensitivity makes a difference as well.
Close miking requires less gain than a more distant mic position.
The recording distance makes a big difference, too. Obviously, you need less gain for screaming rock shouter than for a folk singer, and a snare drum will require less gain than a nylon string guitar. But how much gain is required? Well, it depends. In most home studio situations, the output level of your microphone is way below line level, so you’ll have to turn up the gain control. The most basic task of a microphone preamp is to convert the output of your microphone to line level.
Microphones have an extraordinary dynamic range, so, depending on the recording situation, they can produce a very low or a fairly high output level.
