gstffts32

gstffts32 — FFT functions for signed 32 bit integer samples

Synopsis

#include <gst/fft/gstffts32.h>

                    GstFFTS32;
struct              GstFFTS32Complex;
GstFFTS32 *         gst_fft_s32_new                     (gint len,
                                                         gboolean inverse);
void                gst_fft_s32_fft                     (GstFFTS32 *self,
                                                         const gint32 *timedata,
                                                         GstFFTS32Complex *freqdata);
void                gst_fft_s32_inverse_fft             (GstFFTS32 *self,
                                                         const GstFFTS32Complex *freqdata,
                                                         gint32 *timedata);
void                gst_fft_s32_window                  (GstFFTS32 *self,
                                                         gint32 *timedata,
                                                         GstFFTWindow window);
void                gst_fft_s32_free                    (GstFFTS32 *self);

Description

GstFFTS32 provides a FFT implementation and related functions for signed 32 bit integer samples. To use this call gst_fft_s32_new() for allocating a GstFFTS32 instance with the appropriate parameters and then call gst_fft_s32_fft() or gst_fft_s32_inverse_fft() to perform the FFT or inverse FFT on a buffer of samples.

After use free the GstFFTS32 instance with gst_fft_s32_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_s32_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_s32_window() can comfortably be used.

Be aware, that you can't simply run gst_fft_s32_inverse_fft() on the resulting frequency data of gst_fft_s32_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

GstFFTS32

typedef struct _GstFFTS32 GstFFTS32;

struct GstFFTS32Complex

struct GstFFTS32Complex {
  gint32 r;
  gint32 i;
};

Data type for complex numbers composed of signed 32 bit integers.

gint32 r;

Real part

gint32 i;

Imaginary part

gst_fft_s32_new ()

GstFFTS32 *         gst_fft_s32_new                     (gint len,
                                                         gboolean inverse);

This returns a new GstFFTS32 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 GstFFTS32 instance should be used for the inverse FFT

Returns :

a new GstFFTS32 instance.

gst_fft_s32_fft ()

void                gst_fft_s32_fft                     (GstFFTS32 *self,
                                                         const gint32 *timedata,
                                                         GstFFTS32Complex *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 GstFFTS32 instance with gst_fft_s32_new().

freqdata must be large enough to hold len/2 + 1 GstFFTS32Complex frequency domain samples.

self :

GstFFTS32 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_s32_inverse_fft ()

void                gst_fft_s32_inverse_fft             (GstFFTS32 *self,
                                                         const GstFFTS32Complex *freqdata,
                                                         gint32 *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 GstFFTS32 instance with gst_fft_s32_new().

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

self :

GstFFTS32 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_s32_window ()

void                gst_fft_s32_window                  (GstFFTS32 *self,
                                                         gint32 *timedata,
                                                         GstFFTWindow window);

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

self :

GstFFTS32 instance for this call

timedata :

Time domain samples

window :

Window function to apply

gst_fft_s32_free ()

void                gst_fft_s32_free                    (GstFFTS32 *self);

This frees the memory allocated for self.

self :

GstFFTS32 instance for this call