Nikon D6 Reference Manual page 845

Attenuator
Select [Enable] to reduce microphone gain and prevent audio
distortion when recording movies in loud environments.
Frequency Response
Choose the frequency response of external microphones and
the built-in movie microphone.
Option
S [Wide range]
T [Vocal range] Choose for human voices.
G button U 1 movie shooting menu
G button U 1 movie shooting menu
Record a wide range of frequencies. Choose for
everything from music to the bustling hum of a
city street.
1 The Movie Shooting Menu: Movie Shooting Options
Description
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