---
title: AUMessageChannel
framework: audiotoolbox
role: symbol
role_heading: Protocol
path: audiotoolbox/aumessagechannel
---

# AUMessageChannel

A specification for a bidirectional communication message channel.

## Declaration

```swift
protocol AUMessageChannel
```

## Overview

Overview Audio units and their hosts have unique communication needs. For example, for better audio processing they can exchange musical context. An audio unit implements a class that conforms to AUMessageChannel and returns an instance from messageChannel(for:). A host queries the instance through the channel name. This protocol offers a method to send messages to an audio unit and a block to send messages to the host.

## Topics

### Sending a Message to an Audio Unit

- [callAudioUnit(_:)](audiotoolbox/aumessagechannel/callaudiounit(_:).md)

### Sending a Message to a Host

- [callHostBlock](audiotoolbox/aumessagechannel/callhostblock.md)

## See Also

### Messaging Channels

- [messageChannel(for:)](audiotoolbox/auaudiounit/messagechannel(for:).md)