Tutorials and Topics - Peabody Computer Music

Tutorial 19MIDI Control:SynthesizerThus, the combination of velocity and mod wheel position can affect the modulationindex substantially.Envelope and mod wheel control modulation index• Listening only to MSP (with the volume turned down on your keyboard synth), play asingle- line melody on the MIDI keyboard. As you play, notice the effect that velocityhas on the amplitude, timbre, and rate of attack. Move the mod wheel upward toincrease the over-all brightness of the timbre. You can also use the mod wheel tomodulate the timbre during the sustain portion of the note. Try out the pitch bendwheel to confirm that it has the intended effect on the frequency.SummaryMIDI data can be used to control an MSP synthesis patch much like any othersynthesizer. In normal instrument design, MIDI key number and pitch bend wheelposition are both used to determine the pitch of a played note. The key number must beconverted into frequency information with the mtof object. The pitch bend value must beconverted into the proper frequency bend factor, based on the twelfth-root-of-two persemitone used in equal temperament. Since the designated “no-bend” value of 64 is not inthe precise center of the 0 to 127 range, upward bend must be calculated slightlydifferently from downward bend.Note-on velocity is generally used to determine the amplitude of the note, and triggers theattack portion of the amplitude envelope. The note-off message triggers the releaseportion of the envelope. The velocity value can be used to alter the range of the envelope(or to provide a factor for scaling the amplitude). It is usually best to map velocity toamplitude exponentially rather than linearly. Velocity can also be used to alter the rate ofthe envelope, and/or other parameters such as modulation index.An MSP object can only make one sound at a time, so if you want to play more than onesimultaneous note via MIDI you will need to assign each note a voice number with poly,and route each voice to a different MSP object. In the next tutorial, we’ll use the polyobject to make polyphonic voice assignments for the simple case required for this tutorial.160