View source for User Reference:FFTFilter

==Function==
The FFTFilter applies a [http://en.wikipedia.org/wiki/Short-time_Fourier_transform short-term Fast Fourier Transformation (FFT)] to selected channels of its input signal, resulting in a time series of frequency spectra.
The computed spectra may be displayed in visualization windows. 

Typically, the FFTFilter is used for spectral estimation and demodulation, instead of the [[User Reference:ARFilter|ARFilter]].

==Parameters==

===FFTOutputSignal===
Depending on configuration, the FFT filter's output signal will be the computed spectrum, or the unchanged input.
Possible values are
*0 for input connect-through--<br />this option allows using the FFTFilter for visualization purposes.
*1 for power spectrum--<br />as with the [[User Reference:ARFilter|ARFilter]], the output signal's elements will correspond to frequency bins.
*2 for complex amplitudes--<br />the output will be complex fourier coefficients in [http://www.fftw.org/fftw3_doc/The-Halfcomplex_002dformat-DFT.html halfcomplex format], with the spectrum's imaginary part appended to the real part.

===FFTInputChannels===
A list of input channels for which the FFT is computed. When FFTOutputSignal is set to other than 0, FFTInputChannels list entries determine the correspondence between input and output channels.

===FFTWindowLength===
The length of the input data window over which the FFT is computed, given as a time value in seconds, or the number of signal blocks as in the following examples:
 1.34s
 500ms
 5
The FFT will be computed once per data block. If the length of the input data window exceeds that of a data block, FFT windows will overlap. 
If the data window is shorter than a data block, only the most recent samples will enter into the FFT.

===FFTWindow===
Selects the type of [http://en.wikipedia.org/wiki/Window_function sidelobe suppression window]. Possible values are
*1 for a Hamming window,
*2 for a Hann window,
*3 for a Blackman window.

===VisualizeFFT===
A nonzero value selects visualization of the FFT-computed power spectrum. Independently of the FFTOutputSignal parameter's value, it is always the power spectrum that is visualized.

==States==
None.

==See also==
[[User Reference:ARFilter|ARFilter]]

[[Category:Filters]][[Category:Signal Processing]]