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# FFTInitializeUnityTable

> FFTInitializeUnityTable

Initializes a unity roots lookup table used by Fast Fourier Transform functions.

## Syntax

```cpp theme={null}
void DSP::FFTInitializeUnityTable(  
         XMVECTOR* __restrict pUnityTable,  
         size_t uLength  
)  
```

### Parameters

*pUnityTable*   \_Out\_writes\_(uLength)\
Type: XMVECTOR\* \_\_restrict

Caller-provided array of XMVECTOR elements that will be populated with the unity table values. The array passed to *pUnityTable* must be at least *uLength* elements long.

*uLength*   \_In\_\
Type: size\_t

FFT length in frames (sample count / channel count). *uLength* must be a power of two and greater than 16.

### Return value

Type: void

None.

## Remarks

Once it is initialized, the table does not need to be initialized again unless you require a different FFT length.

Unity tables for FFT lengths of 16 and below are hard-coded into the respective FFT functions: [FFT16](https://docs.xbox.com/reference/audio/xdsp/functions/fft16.md), [FFT8](https://docs.xbox.com/reference/audio/xdsp/functions/fft8.md), and [FFT4](https://docs.xbox.com/reference/audio/xdsp/functions/fft4.md). They do not need to be initialized.

All buffer parameters must be 16-byte aligned. Audio data must be FLOAT32 mono.

## Requirements

**Header:** xdsp.h

**Supported platforms:** XBOX One family consoles and XBOX Series consoles

## See also

[xdsp](https://docs.xbox.com/reference/audio/xdsp/xdsp_members.md)

[FFTInterleaved](https://docs.xbox.com/reference/audio/xdsp/functions/fftinterleaved.md)


## Related topics

- [ButterflyDIT4_4](https://docs.xbox.com/reference/audio/xdsp/functions/butterflydit4_4.md)
- [IFFTDeinterleaved](https://docs.xbox.com/reference/audio/xdsp/functions/ifftdeinterleaved.md)
- [FFTInterleaved](https://docs.xbox.com/reference/audio/xdsp/functions/fftinterleaved.md)
- [FFT](https://docs.xbox.com/reference/audio/xdsp/functions/fft.md)
- [XDSP](https://docs.xbox.com/reference/audio/xdsp/xdsp_members.md)