---
title: "AudioOutputUnitStart(_:)"
framework: audiotoolbox
role: symbol
role_heading: Function
path: "audiotoolbox/audiooutputunitstart(_:)"
---

# AudioOutputUnitStart(_:)

Starts an I/O audio unit, which in turn starts the audio unit processing graph that it is connected to.

## Declaration

```swift
func AudioOutputUnitStart(_ ci: AudioUnit) -> OSStatus
```

## Parameters

- `ci`: The I/O audio unit to start.

## Return Value

Return Value A result code.

## See Also

### Starting and Stopping Output

- [AudioOutputUnitStop(_:)](audiotoolbox/audiooutputunitstop(_:).md)
- [AudioOutputUnitStartProc](audiotoolbox/audiooutputunitstartproc.md)
- [AudioOutputUnitStopProc](audiotoolbox/audiooutputunitstopproc.md)