Wiisp Synth is a simple drone synthesizer built in Pure Data that is controlled by sliders. The idea is to use a very sparse set of audio components and controls that gets the most reactivity.
The design starts with two oscillators are sine waves with adjustable pitch. The second oscillator has a higher pitch range. Both are directed to a delay, with optional FM from oscillator A. LPF controls the frequency of a resonant lowpass filter that is bypassed whenever the slider is set to 0. The filter has FM input from each of the oscillators. Glide creates a smooth transition between changing any of the values.