Tutorials and Topics - Peabody Computer Music

Tutorial 19MIDI Control:SynthesizerThe expr object on the left maps velocity to an exponential curve to determine theamplitude.1.0amplitude00velocity127Velocity mapped to amplitude with an exponent of 4If we used a straight linear mapping, MIDI velocities from 127 to 64 (the range in whichmost notes are played) would cover only about a 6 dB amplitude range. The exponentialmapping increases this to about 24 dB, so that change in the upper range of velocitiesproduces a greater change in amplitude.MIDI control of timbreIt’s often the case that acoustic instruments sound brighter (contain more highfrequencies) when they’re played more loudly. It therefore makes sense to have note-onvelocity affect the timbre of the sound as well as its loudness. In the case of brassinstruments, the timbre changes very much in correlation with amplitude, so in this patchwe use the same envelope to control both the amplitude and the modulation index of theFM instrument. The envelope is sent to a *~ object to scale it into the proper range. The+~ 8 object ensures that the modulation index affected by velocity ranges from 0 to 8(when the note is played with maximum velocity). As we saw earlier, in the main patchthe modulation wheel can be used to increase the modulation index still further (addingup to 8 more to the modulation index range).159