Tutorials and Topics - Peabody Computer Music

Tutorial 7Synthesis:Additive synthesisA variety of complex tonesEven with only six partials, one can make a variety of timbres ranging from “realistic”instrument- like tones to clearly artificial combinations of frequencies. The settings for afew different tones have been stored in a preset object, for you to try them out. A briefexplanation of each tone is provided below.• Click on the ezdac~ speaker icon to turn audio on. Click on the button to play a tone.Click on one of the stored presets in the preset object to change the settings, then clickthe button again to hear the new tone.Preset 1. This tone is not really meant to emulate a real instrument. It’s just a set ofharmonically related partials, each one of which has a different amplitude envelope.Notice how the timbre of the tone changes slightly over the course of its duration asdifferent partials come to the foreground. (If you can’t really notice that change of timbre,try changing the note’s duration to something longer, such as 8000 milliseconds, to hearthe note evolve more slowly.)Preset 2. This tone sounds rather like a church organ. The partials are all octaves of thefundamental, the attack is moderately fast but not percussive, and the amplitude of thetone does not diminish much over the course of the note. You can see and hear that theupper partials die away more quickly than the lower ones.Preset 3. This tone consists of slightly mistuned harmonic partials. The attack isimmediate and the amplitude decays rather rapidly after the initial attack, giving the notea percussive or plucked effect.Preset 4. The amplitude envelopes for the partials in this tone are derived from ananalysis of a trumpet note in the lower register. Of course, these are only six of the manypartials present in a real trumpet sound.Preset 5. The amplitude envelopes for the partials of this tone are derived from the sametrumpet analysis. However, in this case, only the odd-numbered harmonics are used. Thiscreates a tone more like a clarinet, because the cylindrical bore of a clarinet resonates theodd harmonics. Also, the longer duration of this note slows down the entire envelope,giving it a more characteristically clarinet-like attack.Preset 6. This is a completely artificial tone. The lowest partial enters first, followed by thesixth partial a semitone higher. Eventually the remaining partials enter, with frequenciesthat lie between the first and sixth partial, creating a microtonal cluster. The beating effectis due to the interference between these waves of slightly different frequency.101