Canon EOS 80D - Manual (Page 173)

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3 Setting Noise ReductionN
 With [Auto] and [Enable], the noise reduction process after the picture is
taken may take the same amount of time as that for the exposure. You
cannot take another picture until the noise reduction process is
completed.
 Images taken at ISO 1600 or higher may look grainier with the [Enable]
setting than with the [Disable] or [Auto] setting.
 With [Enable], if a long exposure is shot with the Live View image
displayed, “BUSY” will be displayed during the noise reduction process.
The Live View display will not appear until the noise reduction is
completed. (You cannot take another picture.)