ZLPFILT

Purpose:

Performs low pass filtering by zeroing the FFT values.

Syntax:

ZLPFILT(series, fc, mask)

series	-	Input series to filter.
fc	-	Optional. A real, the low 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 low pass filtered output.

Example:

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

W2: zlpfilt(w1, 10)

W1 contains a 1 Hz sinewave with 20 Hz high frequency sinusoidal noise.

W2 filters out the noise an returns the 1 Hz sinusoidal component.

Remarks:

ZLPFILT performs low pass filtering by zeroing out the high 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.