Roland SP-404MK2 Reference Manual page 67

8. Press the [SUB PAD] button.
Sampling begins when the selected pattern chain starts playing back.
If you decide to cancel sampling, press the [EXIT] button.
When pattern chain repeat is set to "REPEAT Off", sampling ends at the same time as pattern chain playback ends.
9. To exit sampling, press the [REC] button.
The sample is saved to the pad.
Combining Samples to Create a Pattern (PATTERN SEQUENCER)
67