Modular synthesizer

VCV Rack in about 90 lines: examples/audio/modular.py.

python examples/audio/modular.py            # a starter patch
python examples/audio/modular.py patch.json # a saved one

It opens with an acid bass line: a sequencer plays an oscillator through a filter, an envelope, an amplifier and a delay, with a scope and the output. Then:

• Add modules from the browser on the left (search or pick a category).
• Drag from one jack to another to plug a cable; outputs are on the dark plates.
• Right-click a jack to unplug it; drag a plugged input to move its cable.
• Drag a module by its title to move it; the × removes it.
• Ctrl+S saves the patch, Ctrl+O opens it again.

How it is built

The whole window is one Rack component on top of the engine:

engine = audio.Engine()
starter_patch(engine)                       # engine.add(...) and engine.connect(...)

class Modular(pz.App):
    layout = {}

    def view(self):
        return ui.rack.Rack(engine=self.engine, layout=self.layout, rows=2)

The rack reads the modules and cables from the engine, draws a panel for each module from its description in the catalog, and writes back every change you make. ui.rack.save() stores the patch and the position of each module in one JSON file. See Cables for how the cables are drawn and animated.