In note modulation, a track's note is altered by one or more tracks. A note modulator track is interpreted as an array of signed offsets (in semitones), which are added to the target track's default note. For example, suppose the target track has a default note of C. If the corresponding step in the note modulator track contains zero, C is output as usual, but if the modulator step contains 3, the target track outputs Eb instead, because C + 3 semitones = Eb.
If a target track has multiple note modulators, they're summed. This means that a pair of note modulations can potentially cancel each other out, for example if one modulator produces 3 and the other produces −3, the net offset is zero, and the target note remains unchanged.
It's often useful to know what notes a given set of note modulators will produce, and whether those notes form a subset of any common scales. For details, see the Table of Addends and Their Associated Pitch Sets.
When many note modulators are summed, the resulting pitch can potentially vary over a large range. This can be addressed by limiting the output to an octave. For more on this, see range and range modulation.
Note modulation usually targets note tracks, but it can also target scale modulators and chord modulators.