ZBSFILT

Purpose:

Performs band stop filtering by zeroing the FFT values.

Syntax:

ZBSFILT(series, fs1, fs2, mask)

series	-	Input series to filter.
fs1	-	Optional. A real, the first band stop cutoff frequency. Defaults to rate(series)/10.
fs2	-	Optional. A real, the second band stop cutoff frequency. Defaults to rate(series)/2.
mask	-	Optional. An integer, return the frequency domain mask only. Defaults to 0, return processed input.

Returns:

A series, the band stop filtered output.

Example:

W1: gsin(1000, 0.001, 10) + gsin(1000, 0.001, 20) + gsin(1000, 0.001, 30) + gsin(1000, 0.001, 40)

W2: zbsfilt(w1, 15, 35)

W1 contains the sum of 10 Hz, 20 Hz, 30 Hz and 40 Hz sinewaves.

W2 filters out the 20 Hz and 30 Hz components leaving a series consisting of 10 Hz and 40 Hz sine components.

Remarks:

ZBSFILT performs band stop filtering by zeroing out the stop band 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 fs1 < 0 or fs2 < 0, no filtering is performed.

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