---
title: "token(byAddingParameterRecordingObserver:)"
framework: audiotoolbox
role: symbol
role_heading: Instance Method
path: "audiotoolbox/auparameternode/token(byaddingparameterrecordingobserver:)"
---

# token(byAddingParameterRecordingObserver:)

Adds a recording observer for a single parameter or all parameters in a group.

## Declaration

```swift
func token(byAddingParameterRecordingObserver observer: @escaping AUParameterRecordingObserver) -> AUParameterObserverToken
```

## Parameters

- `observer`: A block called to record parameter changes.

## Return Value

Return Value A token which can be passed to the removeParameterObserver(_:) or setValue(_:originator:) methods.

## Discussion

Discussion A host can use a recording observer to capture a series of changes to a parameter value as generated by a UI gesture. Unlike a non-recording observer, these callbacks are not throttled. This block is called in an arbitrary thread context and it is responsible for thread-safety. It must not make any calls to add or remove other observers, including itself, as this will deadlock. An audio unit should interact with the parameter node via the implementorValueObserver and implementorValueProvider properties.

## See Also

### Observers

- [token(byAddingParameterObserver:)](audiotoolbox/auparameternode/token(byaddingparameterobserver:).md)
- [token(byAddingParameterAutomationObserver:)](audiotoolbox/auparameternode/token(byaddingparameterautomationobserver:).md)
- [removeParameterObserver(_:)](audiotoolbox/auparameternode/removeparameterobserver(_:).md)