# Multichannel audio

> Audio bundles carry from 1 to 32 channels. Widths are inferred and checked.

Source: https://docs.tune.toys/concepts/multichannel/

An audio cable carries a bundle of between 1 and 32 channels. Stereo is a bundle of two.

## What it does

Ports declare a fixed channel count or an automatic one. Automatic ports adopt the width of what is connected, and sources default to mono unless a count is declared. Strict is the default input policy: widths must match. The Channels section of a node's Properties can adapt narrower inputs with broadcast, pad or repeat; none of these policies reduces a wider input.

Reduction and routing are done explicitly: [Select channels](https://docs.tune.toys/nodes/std.select/) keeps a range, [Channel matrix](https://docs.tune.toys/nodes/std.matrix/) routes and mixes lanes, [Combine channels](https://docs.tune.toys/nodes/std.combine/) joins bundles and [Mixer](https://docs.tune.toys/nodes/std.mixer/) adds them.

Two inputs follow their own rule. A sidechain input named `key`, on the [Compressor](https://docs.tune.toys/nodes/std.compressor/) and [Gate](https://docs.tune.toys/nodes/std.gate/), never changes the node's width: it carries one channel, which then drives every channel, or exactly as many as the node. A [Crossover](https://docs.tune.toys/nodes/std.crossover/) outputs one copy of its input per band, band by band, so three bands of stereo is a six-channel bundle; its band count is set on the node because it decides that width.

## Tips

- A mono output is sent to both monitor channels.
- Monitoring choices are host settings and are not saved in the Toy.

## See also

[Cables](https://docs.tune.toys/concepts/cables/).