---
title: kSpeechSyncCallBack
framework: applicationservices
role: symbol
role_heading: Global Variable
path: applicationservices/kspeechsynccallback
---

# kSpeechSyncCallBack

Set the callback function to be called when the Speech Synthesis Manager encounters a synchronization command within an embedded speech command in text being processed on the speech channel.

## Declaration

```swift
let kSpeechSyncCallBack: CFString
```

## Discussion

Discussion The value associated with this property is CFNumber object whose value is a pointer to an application-defined synchronization callback function, whose syntax is described in SpeechSyncProcPtr. Passing a CFNumber object that contains the value NULL for the value of this property disables the synchronization callback function. This property works with the SetSpeechProperty(_:_:_:) function.