Roland SP-404MK Reference Manual page 32

Playing Back Samples (SAMPLE MODE)
Playing Back Samples in Detailed Steps (ROLL)
You can use the roll function to repeatedly play back samples at a set interval.
1
Hold down the [ROLL] button and press pads [1]‒[16].
The sample plays back as a roll.
You can play back up to four samples at the same time as a roll.
Using a roll during sample playback
You can make a sample roll while it is playing back.
1
Press pads [1]‒[16].
The sample plays back.
2
Press the [ROLL] button to turn the roll on (the button lights up).
The sample plays back rolled.
3
Press the [ROLL] button again to stop the roll while it is playing back.
The roll starts once you take your finger off the [ROLL] button after pressing it.
To play rolls with the correct timing, press the [ROLL] button just before the roll should begin, and take your finger off
the button at the desired timing.