# Modular synthesizer

> A modular synthesizer in Python like VCV Rack — modules on rails, cables you drag between jacks, a module browser, and patches saved to JSON.

Source: https://albakore.github.io/pyzed/audio/demos/modular/

(Image: A modular rack: a cable dragged from the delay to the scope, then the filter's cutoff knob turned)

VCV Rack in about 90 lines: [`examples/audio/modular.py`](https://github.com/albakore/pyzed/blob/main/examples/audio/modular.py).

```bash
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.
- <kbd>Ctrl</kbd>+<kbd>S</kbd> saves the patch, <kbd>Ctrl</kbd>+<kbd>O</kbd> opens it again.

## How it is built

The whole window is one [`Rack`](https://albakore.github.io/pyzed/audio/rack/rack/) component on top of the engine:

```python
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](https://albakore.github.io/pyzed/audio/rack/cables/)
for how the cables are drawn and animated.