# AudioUnitAddRenderNotify(_:_:_:) Registers a callback to receive audio unit render notifications. ``` func AudioUnitAddRenderNotify(_ inUnit: AudioUnit, _ inProc: AURenderCallback, _ inProcUserData: UnsafeMutableRawPointer?) -> OSStatus ``` ## Parameters `inUnit` The audio unit that you want to receive render notifications from. `inProc` The callback that you are registering. `inProcUserData` Custom data that you want to be sent to your callback. Use this, for example, to identify the render listener. ## Return Value A result code. ## Discussion The registered callback function is called both before the audio unit performs its render operations (when the render flag’s pre-render bit is set) and after the audio unit has completed its render operation (the render flag’s post-render bit is set). The `inProc` and `inProcUserData` parameters are treated as a two-part identifier. To remove a render listener, you must pass both these values to the [`AudioUnitRemoveRenderNotify(_:_:_:)`](/documentation/AudioToolbox/AudioUnitRemoveRenderNotify(_:_:_:)) function. --- Copyright © 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)