ZHPFILT

Purpose:

Performs high pass filtering by zeroing the FFT values.

Syntax:

ZHPFILT(series, fc, mask)

series	-	Input series to filter.
fc	-	Optional. A real, the high pass cutoff frequency. Defaults to rate(series)/10.
mask	-	Optional. An integer, return the frequency domain mask only. Defaults to 0, return processed input.

Returns:

A series, the high pass filtered output.

Example:

W1: gsin(1000, 1/1000, 20) + gsin(1000, 1/1000, 1)

W2: zhpfilt(w1, 10)

W1 contains a 20 Hertz sinewave riding on top of a 1 Hertz sinusoidal drift.

W2 filters out the drift an returns the 20 Hertz sinusoidal component.

Remarks:

ZHPFILT performs high pass filtering by zeroing out the low frequency components of the FFT of the input. FFT zeroing is a crude but fast filtering operation. However, the pass band and transition edge of the equivalent filter will exhibit significant ripple.

For a flatter response, use traditional filter design methods such as those offered by DADiSP/Filters.

If fc < 0, no filtering is performed.

If mask == 1, the frequency domain binary mask used to zero out the stop band frequencies is returned.