## gstffts16 gstffts16 — FFT functions for signed 16 bit integer samples |

## Synopsis

    #include <gst/fft/gstffts16.h>

    struct              GstFFTS16;
    struct              GstFFTS16Complex;
    GstFFTS16 *         gst_fft_s16_new                     (gint len,
                                                             gboolean inverse);
    void                gst_fft_s16_fft                     (GstFFTS16 *self,
                                                             const gint16 *timedata,
                                                             GstFFTS16Complex *freqdata);
    void                gst_fft_s16_inverse_fft             (GstFFTS16 *self,
                                                             const GstFFTS16Complex *freqdata,
                                                             gint16 *timedata);
    void                gst_fft_s16_window                  (GstFFTS16 *self,
                                                             gint16 *timedata,
                                                             GstFFTWindow window);
    void                gst_fft_s16_free                    (GstFFTS16 *self);

## Description

GstFFTS16 provides a FFT implementation and related functions for signed 16 bit integer samples. To use this call `gst_fft_s16_new()` for allocating a GstFFTS16 instance with the appropriate parameters and then call `gst_fft_s16_fft()` or `gst_fft_s16_inverse_fft()` to perform the FFT or inverse FFT on a buffer of samples.

After use free the GstFFTS16 instance with `gst_fft_s16_free()`.

For the best performance use `gst_fft_next_fast_length()` to get a number that is entirely a product of 2, 3 and 5 and use this as the `len` parameter for `gst_fft_s16_new()`.

The `len` parameter specifies the number of samples in the time domain that will be processed or generated. The number of samples in the frequency domain is `len`/2 + 1. To get n samples in the frequency domain use 2*n - 2 as `len`.

Before performing the FFT on time domain data it usually makes sense to apply a window function to it. For this `gst_fft_s16_window()` can comfortably be used.

Be aware, that you can't simply run `gst_fft_s16_inverse_fft()` on the resulting frequency data of `gst_fft_s16_fft()` to get the original data back. The relation between them is iFFT (FFT (x)) = x / nfft where nfft is the length of the FFT. This also has to be taken into account when calculation the magnitude of the frequency data.

## Details

### struct GstFFTS16

    struct GstFFTS16 {
    };

Instance structure for GstFFTS16.

### struct GstFFTS16Complex

    struct GstFFTS16Complex {
      gint16 r;
      gint16 i;
    };

Data type for complex numbers composed of signed 16 bit integers.

gint16 `r`; | Real part
gint16 `i`; | Imaginary part

### gst_fft_s16_new ()

    GstFFTS16 *         gst_fft_s16_new                     (gint len,
                                                             gboolean inverse);

This returns a new GstFFTS16 instance with the given parameters. It makes sense to keep one instance for several calls for speed reasons.

`len` must be even and to get the best performance a product of 2, 3 and 5. To get the next number with this characteristics use `gst_fft_next_fast_length()`.

`len` : | Length of the FFT in the time domain
`inverse` : | `TRUE` if the GstFFTS16 instance should be used for the inverse FFT
Returns : | a new GstFFTS16 instance.

### gst_fft_s16_fft ()

    void                gst_fft_s16_fft                     (GstFFTS16 *self,
                                                             const gint16 *timedata,
                                                             GstFFTS16Complex *freqdata);

This performs the FFT on `timedata` and puts the result in `freqdata`.

`timedata` must have as many samples as specified with the `len` parameter while allocating the GstFFTS16 instance with `gst_fft_s16_new()`.

`freqdata` must be large enough to hold `len`/2 + 1 GstFFTS16Complex frequency domain samples.

`self` : | GstFFTS16 instance for this call
`timedata` : | Buffer of the samples in the time domain
`freqdata` : | Target buffer for the samples in the frequency domain

### gst_fft_s16_inverse_fft ()

    void                gst_fft_s16_inverse_fft             (GstFFTS16 *self,
                                                             const GstFFTS16Complex *freqdata,
                                                             gint16 *timedata);

This performs the inverse FFT on `freqdata` and puts the result in `timedata`.

`freqdata` must have `len`/2 + 1 samples, where `len` is the parameter specified while allocating the GstFFTS16 instance with `gst_fft_s16_new()`.

`timedata` must be large enough to hold `len` time domain samples.

`self` : | GstFFTS16 instance for this call
`freqdata` : | Buffer of the samples in the frequency domain
`timedata` : | Target buffer for the samples in the time domain

### gst_fft_s16_window ()

    void                gst_fft_s16_window                  (GstFFTS16 *self,
                                                             gint16 *timedata,
                                                             GstFFTWindow window);

This calls the window function `window` on the `timedata` sample buffer.

`self` : | GstFFTS16 instance for this call
`timedata` : | Time domain samples
`window` : | Window function to apply

### gst_fft_s16_free ()

    void                gst_fft_s16_free                    (GstFFTS16 *self);

This frees the memory allocated for `self`.

`self` : | GstFFTS16 instance for this call