During live pattern playback, it is possible to use the Auto Fill feature to insert fill rhythms during the pattern. The RD-8 will continue playing the selected pattern before Auto Fill was enabled, unless the pattern was changed during the fill.

Autofill patterns are created in the same way as a normal pattern and there is up to 64 steps available on each patterns autofill. 

Once you have programmed the Auto Fill patterns use them by pressing the AUTO FILL button and selecting one of the 4 flashing Auto Fill step keys.