Tutorials and Topics - Peabody Computer Music

Tutorial 19MIDI Control:SynthesizerThe pack and line~ objects are used to make the frequency factor change gradually over 20milliseconds, to avoid creating the effect of discrete stepwise changes in frequency.Mod wheelThe mod wheel is used here to change the modulation index of our FM synthesis patch.The mapping is linear; we simply divide the MIDI controller values by 16 to map theminto a range from 0 to (nearly) 8. The precise way this range is used will be seen when welook at the synthesis instrument itself.Controller values mapped into the range 0 to 7.9375The FM synthesizer• Double-click on one of the synthFMvoice~ subpatch objects to open its Patcherwindow.The basis for this FM synthesis subpatch is the simpleFM~ subpatch introduced (andexplained) in Tutorial 11. A typed-in argument is used to set the harmonicity ratio at 1,yielding a harmonic spectrum. The MIDI messages will affect the frequency and themodulation index of this FM sound. Let’s look first at the way MIDI note and pitch bendinformation is used to determine the frequency.MIDI-to-frequency conversionThe object mtof is not a signal object, but it is very handy for use in MSP. It converts aMIDI key number into its equivalent frequency.Calculate the frequency of a given pitch156