The proper setting for a recorder's input controls depends as well on the sensitivity of your microphones. Many professional condenser microphones put out about 10 mV at 1 Pascal (ca. 94 dB SPL), but some very good microphones put out only 1/10 as much (i.e. 20 dB lower), while others (e.g. Neumann M 149) put out nearly 5 times that much (i.e. 14 dB higher).
The factors that you always need to consider are the sensitivity of the microphones, the maximum SPL where the microphones are placed, and the sensitivity (and overload point) of the recorder's inputs.
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