Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!uunet!crdgw1!ge-dab!sunny!harrison From: harrison@sunny.DAB.GE.COM (Gregory Harrison) Newsgroups: comp.dsp Subject: Re: FFTs of Low Frequency Signals Message-ID: <2631@ge-dab.GE.COM> Date: 11 Nov 89 04:41:01 GMT References: <10208@cadnetix.COM> <89Nov8.111523est.30802@snow.white.toronto.edu> Sender: news@ge-dab.GE.COM Reply-To: harrison@sunny.UUCP (Gregory Harrison) Distribution: usa Organization: GE Simulation & Control Systems Dept., Daytona Beach, FL Lines: 22 In article fineberg@caip.rutgers.edu (Adam B. Fineberg) writes: >only be improved by increasing the observation time. Localizing in >frequency is always inversely proportional to localizing in time (the >uncertainty principle). Therefore if you want to localize in >frequency (have better resolution) you must give up localization in >time (use longer observation time). Without some form of constrained >optimization that is the best you can hope for. The Wigner Distribution permits excellent time-frequency localization, far surpassing an FFT in this regard. Certain other difficulties arise with the Wigner Distribution (WD), primarily the generation of cross-term interference which looks like signal energy where there is none. But the cross-term interference occurs at well defined time-frequency locations and as such its effect can be avoided in many circumstances. The time-frequency localization avoids smearing in time and frequency. Highly precise characterizations of nonstationary signals may be gained using the WD, or Discrete WD (DWD). Greg Harrison My opinions are not intended to reflect those of GE.