Fill Patterns are the key to creating expressive drum parts. However, Fill is a sophisticated
feature that requires some explanation.
Remember that Fills are always the same length, and use the same Drum Set, as the associated Main Pattern. This lets you "drop in" a Fill at any time. As soon as you press the FILL button, the Fill takes over from the Main Pattern and starts playing until the end of the Fill.
Generally, Fills are transitional Patterns. Example: Suppose an 8-beat A Main Pattern is playing and you press the FILL button on beat 4. The A Fill Pattern will play the last 4 beats and then automatically transition into the B Main Pattern. Conversely, if B Main is playing and you press Fill, after B Fill has played, the SR-16 will transition to the A Main Pattern. You can select the Fill at any time the Main Pattern is playing.
However, Fills do not have to be transitional Patterns. If you press the FILL button (or footswitch) before the Fill has finished playing and hold it down until after the Fill has played (i.e., past the downbeat of the next Pattern), the SR-16 will return to the original Main Pattern.
Example: Suppose an 8-beat A Main Pattern is playing and you press the FILL button on beat 4 but hold it down past beat 8. The A Fill Pattern will play the last 4 beats, then the SR-16 will return to the A Main Pattern.
Fills cannot start on the downbeat since a Fill, by definition, starts at some point into the Main Pattern. However, anything you record on the Fill downbeat will play on the first downbeat following the Fill (i.e., the downbeat of the next Pattern). To show why this is a useful feature, consider that when coming out of a fill, you'll often want to hit something like a cymbal crash on the downbeat of the next Pattern yet not have that crash repeat every time the Pattern plays. This way of handling Fills lets the downbeat cymbal crash be part of the Fill instead of the Pattern.
A footswitch plugged into the Count/A/B/Fill jack duplicates the FILL button function when playing Patterns in Perform mode.