Canon Rebel T2i Quick Start Manual page 82

Audio Output Levels for Rode Microphone
• The Canon DSLR camera has an automatic level adjustment that adds a constant
hiss to any audio signal using the microphone input.
• An "acceptable" recording depends on the signal to noise ratio. Record speech at
the -10 dB output level and 0 dB input level. Only use the -20 dB level for loud
subjects.
• If the speaker under four feet (1.2 m) from the camera use the -10 dB level. If the
speaker is between 4 and 7 feet (2.1 m) from the camera use the 0 dB level. Don't
use this microphone if the person is much beyond that distance from the camera.
• These output level settings pertain to using this microphone with this model of
camera. Later Canon Rebel models may have improved the automatic level
adjustment. The Sony DSLRs in the CDA depot have better manual control
microphone inputs although they are still quite noisy.