Fw: [geonet]: Bandpass Filtering

[skyhunter]

----- Original Message ----- From: skyhunter To: GEONET Sent: Wednesday, July 10, 2002 12:33 PM Subject: Fw: [geonet]: Bandpass Filtering   ----- Original Message ----- From: Lorraine Godwin To: '[EMAIL PROTECTED]' Sent: Wednesday, July 10, 2002 11:55 AM Subject: RE: [geonet]: Bandpass Filtering Hi Aaron,   Would you mind posting the following to geonet? We're having a problem posting messages from inside Geosoft.   Thanks a lot, Lorraine Godwin   Elizabeth Baranyi from Geosoft also replied to Aaron on this offline. Here is her reply:   Aaron;   This is indeed know as the Gibbs phenomenon, and is due to the Digital Fourier transformation ( DFT) process.  The Digital Fourier Transform of a square box is a Sync function  (sin (x)/x) which is basically a  sinusoidal signal.  The Fourier transform of  a Gaussian signal is a Gaussian signal.  In order to avoid the oscillation artefact, or the Gibbs phenomenon, it is common practice to smooth out the abrupt edges prior to the DFT process.  I can elaborate further would you require more clarifications.   Regards - Elizabeth -----Original Message----- From: skyhunter [mailto:[EMAIL PROTECTED]] Sent: Wednesday, July 10, 2002 11:07 AM To: GEONET Subject: [geonet]: Bandpass Filtering Hi everyone,   I was wondering if anyone can explain to me in simple terms why a bandpass filter tends to oscillate. For example, when applying a bandpass filter to a simple step function between 0 and 1, the resulting bandpass filter oscillates between very negative and very positive numbers in the vicinity of the step-up and step-down. Does anyone have any ideas of how to prevent or minimize these oscillations?     Aaron Balasch Sky Hunter Technologies Inc. Suite 101, 1725 10th Avenue S.W. Calgary, Alberta T3C 0K1 email: [EMAIL PROTECTED] phone: 403-228-2175 fax: 403-244-7955