Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!ncar!asuvax!mcdphx!udc!chant!aglew From: aglew@urbana.mcd.mot.com (Andy-Krazy-Glew) Newsgroups: comp.dsp Subject: Re: What's a waterfall display? Message-ID: Date: 19 Oct 89 00:01:11 GMT References: <1989Oct16.213117.20589@polyslo.CalPoly.EDU> <4999@orca.WV.TEK.COM> Sender: aglew@urbana.mcd.mot.com Distribution: na Organization: Work: Motorola MCD, Urbana Design Center; School: University of Illinois at Urbana-Champaign Lines: 34 In-reply-to: mhorne@ka7axd.WV.TEK.COM's message of 17 Oct 89 16:32:09 GMT "Waterfall display" sounds like what I have seen [*] called a "cascade plot". Usually they were a representation of how the frequency content of a signal changes over time - ie. they were FFT spectra taken over successive intervals, in a pseudo-3D representation. Draw FFT#1 at the baseline. Draw FFT#2 at the baseline + dX,dY; choose dX,dY so that you get very nearly parallel lines, and not too much detail is hidden behind the peaks (actually, varying dX,dY interactively can be very useful too. Sort of like looking at a signal in perspective - but different). Ditto FFT#3, 4, 5... This gives you a 3D looking plot where you can see the frequency components changing over time. Patterns emerge very clearly. In my own work I have used cascade plots to inspect computer performance data, like variations in kernel profiles according to workload. Occasionally I have wanted '4D' or greater type cascade plots, where the underlying data is more than 2D, varying over time. [*] Hell, I'll be honest: "I have seen" == my Dad uses; my Dad is one of the Vibrations Analysis wizards that kept the Canadian Navy going on the oldest destroyers in the world. I keep thinking that some knowledge engineer should interview him to build an expert system for this sort of maintenance and signal processing, now that he's retired. -- Andy "Krazy" Glew, Motorola MCD, aglew@urbana.mcd.mot.com 1101 E. University, Urbana, IL 61801, USA. {uunet!,}uiucuxc!udc!aglew My opinions are my own; I indicate my company only so that the reader may account for any possible bias I may have towards our products.