A sample, unlike the cycles of an oscillator for example, is a finite quantity. There is a sample start and end. To get samples to play for as long as you press down the keys on your keyboard, they need to be looped.
For this to work properly, you have to first set up two loop points which determine the part of the sample that will be looped, and make this a part of the audio file. You cannot set loop points in the NN-19, this has to be done in a sample editor.
All included samples already have set loop points (if needed).
For each sample (or key zone), you can select the following Loop modes by using the Loop knob below the keyboard display:
No looping is applied to the sample.
The part between the loop points plays from start to end, then the cycle is repeated. This is the most common loop mode.
The part between the loop points plays from start to end, then from end to start (backwards), and then repeats the cycle.
For samples without any loop points, the whole sample will be looped.