Most samplers allow the patch programmer to choose to define a loop segment within a sample, which is repeated as long as the envelope generator remains within the sustain phase, so that a sampled sound can be made to sustain indefinitely, or repeat a phrase indefinitely. The loop mode tells the sampler how to repeat the loop portion. A few common loop modes:
- Foward: The sampler plays the loop to its end loop point, and then jumps back to the starting loop point.
- Reverse: The sampler plays the loop from its end loop point backwards to the start loop point, and then jumps back to the end loop point.
- Alternating or forward-reverse: The sampler players the loop from its start loop point to its end loop point. It then reverses direction and plays from the end back to the start loop point, where it changes direction and plays forward again, etc.
There are often combination modes available. For example, "forward + 1" mode on a Roland S770 plays the loop in the forward mode until the performer lets the key up and the envelope generator enters the release phase. Then, at the end of the next loop, it continued playing past the end loop point to the end of the sample, or to a defined stop point.
The means by which loop points have to be chosen to obtain a clean transition at the start/end of the loop can vary depending on the chosen loop mode. A common issue in designing sample-based patches is that the programmer chooses loop points that work well in one mode, but then decides to change the loop mode, and in the new mode the sample clicks or pops at the repeats; new loop points have to be chosen for the new mode.