<!--
{
  "availability" : [
    "iOS: 9.0.0 -",
    "iPadOS: 9.0.0 -",
    "macCatalyst: 13.1.0 -",
    "macOS: 10.11.0 -",
    "tvOS: 9.0.0 -",
    "visionOS: 1.0.0 -"
  ],
  "documentType" : "symbol",
  "framework" : "AudioToolbox",
  "identifier" : "/documentation/AudioToolbox/AUAudioUnit/scheduleParameterBlock",
  "metadataVersion" : "0.1.0",
  "role" : "Instance Property",
  "symbol" : {
    "kind" : "Instance Property",
    "modules" : [
      "Audio Toolbox"
    ],
    "preciseIdentifier" : "c:objc(cs)AUAudioUnit(py)scheduleParameterBlock"
  },
  "title" : "scheduleParameterBlock"
}
-->

# scheduleParameterBlock

The block that hosts use to schedule parameters.

```
var scheduleParameterBlock: AUScheduleParameterBlock { get }
```

## Discussion

As with the render block, a host should fetch this block before beginning to render, if it intends to schedule parameters.

The block is safe to call from any thread context, including realtime audio render threads. Subclasses should not override this; it is implemented in the base class and will schedule the events to be provided to the [`internalRenderBlock`](/documentation/AudioToolbox/AUAudioUnit/internalRenderBlock) implementation

This version 3 property is bridged to the version 2 [`AudioUnitScheduleParameters(_:_:_:)`](/documentation/AudioToolbox/AudioUnitScheduleParameters(_:_:_:)) API.

---

Copyright &copy; 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)