## gstfftf64 gstfftf64 — FFT functions for 64 bit float samples |

## Synopsis

    #include <gst/fft/gstfftf64.h>

                        GstFFTF64;
                        GstFFTF64Complex;
    GstFFTF64*          gst_fft_f64_new                     (gint len,
                                                             gboolean inverse);
    void                gst_fft_f64_fft                     (GstFFTF64 *self,
                                                             const gdouble *timedata,
                                                             GstFFTF64Complex *freqdata);
    void                gst_fft_f64_inverse_fft             (GstFFTF64 *self,
                                                             const GstFFTF64Complex *freqdata,
                                                             gdouble *timedata);
    void                gst_fft_f64_window                  (GstFFTF64 *self,
                                                             gdouble *timedata,
                                                             GstFFTWindow window);
    void                gst_fft_f64_free                    (GstFFTF64 *self);

## Description

GstFFTF64 provides a FFT implementation and related functions for 64 bit float samples. To use this call `gst_fft_f64_new()` for allocating a GstFFTF64 instance with the appropiate parameters and then call `gst_fft_f64_fft()` or `gst_fft_f64_inverse_fft()` to perform the FFT or inverse FFT on a buffer of samples.

After use free the GstFFTF64 instance with `gst_fft_f64_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_f64_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_f64_window()` can comfortably be used.

Be aware, that you can't simply run `gst_fft_f32_inverse_fft()` on the resulting frequency data of `gst_fft_f32_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

### GstFFTF64

    typedef struct {
    } GstFFTF64;

Instance structure for GstFFTF64.

### GstFFTF64Complex

    typedef struct {
      gdouble r;
      gdouble i;
    } GstFFTF64Complex;

Data type for complex numbers composed of 64 bit float.

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

### gst_fft_f64_new ()

    GstFFTF64*          gst_fft_f64_new                     (gint len,
                                                             gboolean inverse);

This returns a new GstFFTF64 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 GstFFTF64 instance should be used for the inverse FFT
Returns : | a new GstFFTF64 instance.

### gst_fft_f64_fft ()

    void                gst_fft_f64_fft                     (GstFFTF64 *self,
                                                             const gdouble *timedata,
                                                             GstFFTF64Complex *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 GstFFTF64 instance with `gst_fft_f64_new()`.

`freqdata` must be large enough to hold `len`/2 + 1 GstFFTF64Complex frequency domain samples.

`self` : | GstFFTF64 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_f64_inverse_fft ()

    void                gst_fft_f64_inverse_fft             (GstFFTF64 *self,
                                                             const GstFFTF64Complex *freqdata,
                                                             gdouble *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 GstFFTF64 instance with `gst_fft_f64_new()`.

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

`self` : | GstFFTF64 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_f64_window ()

    void                gst_fft_f64_window                  (GstFFTF64 *self,
                                                             gdouble *timedata,
                                                             GstFFTWindow window);

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

`self` : | GstFFTF64 instance for this call
`timedata` : | Time domain samples
`window` : | Window function to apply

### gst_fft_f64_free ()

    void                gst_fft_f64_free                    (GstFFTF64 *self);

This frees the memory allocated for `self`.

`self` : | GstFFTF64 instance for this call