gstffts16: GStreamer Base Plugins 1.0 Library Reference Manual

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

## Functions

GstFFTS16 * | gst_fft_s16_new ()
void | gst_fft_s16_fft ()
void | gst_fft_s16_inverse_fft ()
void | gst_fft_s16_window ()
void | gst_fft_s16_free ()

## Types and Values

| GstFFTS16
struct | GstFFTS16Complex

## Includes

    #include <gst/fft/gstffts16.h>

## 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.

## Functions

### 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()`.

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#### Parameters

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.

#### Parameters

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.

#### Parameters

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.

#### Parameters

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` .

#### Parameters

self | GstFFTS16 instance for this call |

## Types and Values

### GstFFTS16

    typedef struct _GstFFTS16 GstFFTS16;

### struct GstFFTS16Complex

    struct GstFFTS16Complex {
      gint16 r;
      gint16 i;
    };

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

#### Members

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