# TweakKnob

Changes the value of a knob.

### Synopsis

`Err TweakKnob (Item KnobItem, int32 Value)`

### Description

This function sets the value of a knob that is attached to an instrument. The value is clipped to the allowable range. This has been optimized to allow rapid modulation of sound parameters.

This function differs from `TweakRawKnob()` in that the value passed to this function goes through knob-specific conversion. For example, typically frequency knobs are controlled with a frac16 Hz value with this function, and with a phase increment value with `TweakRawKnob()`. For many other knobs, the conversion is trivial: `TweakRawKnob()` and `TweakKnob()` yield the same results.

The current raw value of the Knob can be read by `GetAudioItemInfo()` using the AF_TAG_CURRENT_VALUE tag. There is no inverse conversion function, however, to convert back to the units supplied to `TweakKnob()`.

If this knob is connected to the output of another instrument via `ConnectInstruments()`, the tweaked value is ignored until that connection is broken.

### Arguments

KnobItem
  Item number of the knob to be tweaked.

Value
  The new value for that knob.

### Return Value

The function returns a non-negative value if successful or an error code (a negative value) if an error occurs.

### Implementation

SWI implemented in Audio folio V20.

### Associated Files

audio.h

### See Also

``TweakRawKnob`(), GrabKnob(), Knob`