butterworth filter

Hello, I am an italian cardiologist and with the help of other coders from RAC I made a nice VB6 program to analyze digitally stored ElectroCardioGrams. I use this program for educational purposes. One of the most interesting aspects of ECG analysis is linked to ECG signal filtering. To analyze the impact of different filters to the appearance and diagnostic relevance of filtered ECG recordings I use (so far) the computations provided by this Web site: [login to view URL]~fisher/mkfilter An example: Specifying these parameters: filtertype = Butterworth passtype = Bandpass order = 2 samplerate = 300 corner1 = 1 corner2 = 40 I get from the Web site these "coefficients" written in C code: #define GAIN 9.413148578e+00 static void filterloop() { for (;;) { xv[0] = xv[1]; xv[1] = xv[2]; xv[2] = xv[3]; xv[3] = xv[4]; xv[4] = next input value / GAIN; yv[0] = yv[1]; yv[1] = yv[2]; yv[2] = yv[3]; yv[3] = yv[4]; yv[4] = (xv[0] + xv[4]) - 2 * xv[2] + ( -0.3197324699 * yv[0]) + ( 1.5285630711 * yv[1]) + ( -3.0854919004 * yv[2]) + ( 2.8764697661 * yv[3]); next output value = yv[4]; } } Although I don't know C code, the routine is easy enough to be translated in VB6. Well, in my program I already wrote some routines with already defined filtering criteria, but I wish I could make the computations of the Butterworth filter at runtime, changing the corner frequencies and getting the corresponding coefficients. This way I could evaluate the impact of different filters of the ECG morphology without the need to stop the program, copy the coefficients from the Web site, paste them, an so on. I hope you can help me. Thanks in advance. Dario Barbieri ## Deliverables 1) Complete and fully-functional working program(s) in executable form as well as complete source code of all work done. 2) Deliverables must be in ready-to-run condition, as follows (depending on the nature of the deliverables): a) For web sites or other server-side deliverables intended to only ever exist in one place in the Buyer's environment--Deliverables must be installed by the Seller in ready-to-run condition in the Buyer's environment. b) For all others including desktop software or software the buyer intends to distribute: A software installation package that will install the software in ready-to-run condition on the platform(s) specified in this bid request. 3) All deliverables will be considered "work made for hire" under U.S. Copyright law. Buyer will receive exclusive and complete copyrights to all work purchased. (No GPL, GNU, 3rd party components, etc. unless all copyright ramifications are explained AND AGREED TO by the buyer on the site per the coder's Seller Legal Agreement). ## Platform Windows XP Visual Basic 6