The Zplane program

The Zplane program made 16 figures for this paper book. In the electronic book, each of those 16 figure captions contains a pushbutton that activates Zplane and initializes it to that figure. Zplane has a built-in tutorial that enables you to operate it without this document. Huge gaps between the abstract and the concrete are bridged by Zplane. First is the conceptual gap from the time-domain representation of a filter to its poles and zeros in the complex frequency plane (as described in chapter ). Second is a gap from the appearance of a filter to the appearance of field data after applying it. Zplane gives you hands-on experience with all these relationships. Z-plane theory conveniently incorporates causality and relates time and frequency domains. With Zplane, you create and move poles and zeros in the complex Z-plane. You immediately see the filter impulse response and its spectrum as you readjust the poles and zeros. If you choose to touch a plane of seismograms, it is filtered by your chosen filter and redisplayed after a few seconds.

Choice of a display filter is important for both field data and synthetic data. Goals for filter design that are expressed in the frequency domain generally conflict with other goals in the time domain. For example, when a filter is specified by frequency cutoffs and rolloffs, then the time-domain behavior, i.e., filter length, phase shift, and energy delay, are left to fall where they may.