Zoom F6 Operation Manual page 112

NOTE
In situations where the sound being recorded can be heard at the head-
phone monitoring position, sound waves traveling through the air can inter-
fere with the sound heard from the headphones, altering the monitored
sound. The more the sound heard through the headphones is delayed and
the lower its volume, the greater the impact of the sound waves.
Digital Boost adds a set boost volume to the adjusted headphone volume
level, reducing the impact of the sound waves that travel through the air.
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