The probability feature on the RD-8 allows to to add some humanization to your pattern, allowing you to adjust how likely a voice is to be played. The higher the number, the more likely it is to sound. To adjust this:

1. Press SETTINGS.
2. Press PROB (STEP BUTTON 9).
3. Select the voice you wish to give probability to.
4. Use the step keys and length navigation arrows to enable probability on the steps (up to 64 steps) you require.
5. Use the DATA knob to adjust the probability rating
6. Press SETTINGS twice to confirm