Tutorials and Topics - Peabody Computer Music

Tutorial 18MIDI Control:Mapping MIDI to MSPequal powers of 2. (See the discussions of pitch-to-frequency conversion in Tutorial 17and Tutorial 19.)• Type the number 1 (or choose “Octave Pitch Bend” from the umenu) to direct thecontroller values to affect the carrier frequency. Move the mod wheel to bend thepitch upward as much as one octave, and back down to the original frequency.In order for the mod wheel to perform a pitch bend of one octave, we map its range ontothe range 0 to 1. This number is then used as the exponent in a power of 2 function andmultiplied times the fundamental frequency in expr.Octave bend factor ranges from 20 to 212 0 = 1, and 2 1 = 2, so as the control value goes from 0 to 1 the carrier frequency increasesfrom 220 to 440, which is to say up an octave. The increase in frequency from 220 to 440follows an exponential curve, which produces a linear increase in perceived pitch from Ato A.Mapping MIDI to modulation indexMapping the MIDI controller to the modulation index of the FM instrument is muchsimpler, because a linear control is what’s called for. Once the controller values areconverted by the map subpatch, no further modification is needed. The mod wheel variesthe modulation index from 0 (no modulation) to 24 (extreme modulation).• Type the number 4 (or choose “Modulation Index” from the umenu) to direct thecontroller values to affect the modulation index. Move the mod wheel to change thetimbre of the tone.152