I just added this to the page for my piece Gates (No. 1).
Gates (No. 1) is a software instrument, programmed in Pure Data. Inspired by other instrument builders, particularly David Tudor’s electronic instruments, Gates (No. 1) provides the performer with high-level control of musical events, while the moment-to-moment details emerge from the patch itself.
The main interface for Gates (No. 1).
Central to the sound of the instrument is a set of three feedback networks. Implemented using recursive delay lines, each network emphasizes a particular frequency range: low, medium, and high. The frequency ranges are user-selectable, allowing for coarse control over the register of a particular musical event. Slight changes in delay time and filter cutoffs destabilize the feedback, producing glissandi and other effects.
Feedback network producing low frequency sounds.
The pitch register is selected through a combination of key-presses, which also determines other parameters of the sound. The first of those other parameters is a selection of one of 6 sound-processing algorithms which is applied to the selected feedback network. The 6 processing types are: amplitude modulation by line segments, ring modulation by filtered noise, ring modulation by a sine wave, recursive delay with delay time modulation, a chorus effect, and a set of bandpass filters in series (creating phase cancellations).
ASCII-based input module.
Inner workings of the patch. Above are the different processing modules, routed through an echo effect, and out to the DAC.
The second parameter is a selection of one of 50 different, hand-drawn wave shapes. The wave shapes provide control data for the modulation sources described above.
One set of wave shapes, used to control the sound processing modules.
The key-press combination also determines the duration and number of repeats of a sound, ranging from short, repetitive events to long drones. Finally, the performer can choose to route the output of the instrument through a secondary processing unit, which modifies its processing algorithms according to the rhythmic onsets of the generated sound.
The secondary effects module adds a layer of digital grit, contrasting with the cleaner sounds of the instrument.
The variety and diversity of sound generation, processing, and control algorithms ensure that the instrument is never fully under the control of the performer. Rather than a flaw, this is a feature, as it ensures an exciting challenge for the performer, and produces performances which can retain similar characteristics while varying widely in structure and duration.