Rapid permutation of a given number of tones (between 2 - 6) within the indicated register(s). The sequence of these sounds must be completely irregular so that no patterns or "motivs" are occuring. The speed of the trill is generally fast, with three different types of processes: accelerando, ritardando, or constant (also with "rubato"). Each TRILL starts soft, increases in loudness, and fades out in the end.