Roland SP-404MKII Creative Sampler and Effector - Manual (Page 34)

Using the Effects
34
Turning Effects On/Off at the Desired Timing
You can make effects apply only while you hold down the effect buttons (EFFECT GRAB).
This lets you quickly turn an effect on/off in time with what you play.
1. Play back a sample.
2. While holding down the [VALUE] knob, press an effect button (such as the [FILTER+DRIVE] button).
The effect turns on only while you’re pressing the effect button.