Band Pass Filter

Use the Database Tools > Filters > Band Pass Filter menu option (BANDPASS GX) to apply a band-pass filter to a channel.

Band Pass Filter dialog options

Channel to filter

Name of the Input Channel.

Script Parameter: BANDPASS.IN

Output channel

Name of the output channel (created if does not exist).

Script Parameter: BANDPASS.OUT

Short wavelength cutoff (fiducials)

Short Wavelength cutoff values in fiducials.

Script Parameter: BANDPASS.SHORTW

Long wavelength cutoff (fiducials)

Long Wavelength cutoff values in fiducials.

Script Parameter: BANDPASS.LONGW

Filter length

Number of coefficients (filter length), 0 for a default length.

Script Parameter: BANDPASS.FILTLEN

Application Notes

A band-pass filter changes channel data such that features longer than the long wavelength cutoff and shorter than the short wavelength cutoff will be removed. This is done by calculating an appropriate convolution filter (after Fraser, 1966) and applying that filter.

The length of the filter can be specified or calculated by default. The default length will be determined from the length of the longest wavelength being removed. A band-pass filter is considered linear because all data is treated by the filter equally. This can be a problem when attempting to remove short- wavelength, but high amplitude features because quite strong filters may be required. Such filters can affect parts of the data that you did not intend to disturb. An alternative is to use a non-linear filter such as NLFILT.