FFTP

Purpose:

Calculates the Fast Fourier transform of a series in polar (Magnitude/Phase) form.

Syntax:

FFTP(series, len)

series	-	Any series or multi-column table.
len	-	Optional. An integer, the FFT length. Defaults to the length of the input series. If len > length(series), the series is padded with zeros.

Returns:

A complex series or table in Polar form.

Example:

W1: gsin(1000, 0.001, 50)

W2: fft(w1, 1024)

W3: fftp(w1, 1024)

Although W2 and W3 are identical in terms of the complex result, W2 contains the FFT result in Cartesian form, a + bi, while W3 represents the result in polar form Me^iθ. For plotting purposes, W2 displays the real part of the FFT and W3 displays the magnitude part.

Remarks:

The FFTP result is complex polar and the magnitude of the resultant series is plotted. A mixed radix algorithm is employed to compute the FFT.

FFTP uses the same algorithm as the FFT but is slightly slower because it calculates magnitude/phase.

Use SPECTRUM to produce a normalized magnitude plot.

References:

Oppenheim and Schafer.

Digital Signal Processing

Prentice Hall, 1975

Digital Signal Processing Committee

Programs for Digital Signal Processing

I.E.E.E. Press, 1979