Canon EOS-1D X Mark III DSLR Camera (Body Only) - Manual (Page 286)

Attenuator
Automatically suppresses sound distortion caused by loud noises. Even if [ Sound rec. ] is
set to [ Auto ] or [ Manual ] for recording, sound distortion may still result if there is a very loud
sound. In this case, setting it to [ Enable ] is recommended.
Microphone
Normally, monaural sound is recorded with the built-in movie microphone.
Stereo sound can be recorded by connecting an external microphone with a 3.5 mm
mini-jack to the camera's external microphone IN terminal (
), which the camera will
use instead. Using an external microphone such as Directional Stereo Microphone
DM-E1 (sold separately) is recommended.
Line input
Direct input is supported for line-out stereo sound from mixers or other devices. Audio
from a 3.5 mm mini-jack connected to the camera's line input terminal (
) is combined
with video to record movies with stereo sound. The standard input level is –8 dBV.
Adjust the audio recording level to suit the line-out level.
Headphones
By connecting commercially available headphones with a 3.5 mm mini-jack to the
headphone terminal (
), you can listen to the sound as movies are recorded. You can
listen in stereo to audio from an external stereo microphone. To adjust headphone
volume, press the <
> button, select < >, then turn the < > dial for adjustment
( ).
You can also use headphones during movie playback.
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