# FILTERING - HELP

Started by October 20, 2003
 Hello I am new to the group and in fact new to signal processing and filtering and was wondering if anyone could help me with a problem I have filtering in MATLAB. Firstly I should say that I have a large number of waveforms (>5000) and from each wish to extract the fundamental and second harmonic waveform components. Ultimately I really need to fully automate the process as there are so many waveforms. I am trying to construct an N-th order bandpass digital elliptic filter using the command: [B,A] = ELLIP(N,Rp,Rs,Wn) where Wn is a two- element vector, Wn = [W1 W2] with 0.0 < Wn < 1.0, with 1.0 corresponding to the Nyquist frequency. The parameters Rp and Rs respectively define the Passband ripple, in decibels and the Stopband attenuation, in decibels. Can someone please explain to me what this actually means and how I go about identifying values for Rp and Rs? Perhaps if I can successfully generate a filter for one waveform the process will become clearer to me and I can then think about automating the procedure. Will that be possible? I guess I will need to be able to calculate appropriate values for the parameters N,Rp,Rs and Wn for each waveform. I can see how to calculate Wn for the different waveforms, as this will just be the width of the window I choose, and N can be derived using the ELLIPORD function. However, calculating Rp and Rs for each waveform is not at all clear. All my waveforms have a fundamental frequency between 1 and 10MHz so that the maximum value of the second harmonic is approximately 20MHz. Thanks in advance. Regards Calum Macdonald
 Calum, Maybe you can use FFT and peak detection on FFT bin magnitude to identify the location of fundamental frequency on each waveform. This way you don't need the bandpass filter. camdmag <> wrote: Hello I am new to the group and in fact new to signal processing and filtering and was wondering if anyone could help me with a problem I have filtering in MATLAB. Firstly I should say that I have a large number of waveforms (>5000) and from each wish to extract the fundamental and second harmonic waveform components. Ultimately I really need to fully automate the process as there are so many waveforms. I am trying to construct an N-th order bandpass digital elliptic filter using the command: [B,A] = ELLIP(N,Rp,Rs,Wn) where Wn is a two- element vector, Wn = [W1 W2] with 0.0 < Wn < 1.0, with 1.0 corresponding to the Nyquist frequency. The parameters Rp and Rs respectively define the Passband ripple, in decibels and the Stopband attenuation, in decibels. Can someone please explain to me what this actually means and how I go about identifying values for Rp and Rs? Perhaps if I can successfully generate a filter for one waveform the process will become clearer to me and I can then think about automating the procedure. Will that be possible? I guess I will need to be able to calculate appropriate values for the parameters N,Rp,Rs and Wn for each waveform. I can see how to calculate Wn for the different waveforms, as this will just be the width of the window I choose, and N can be derived using the ELLIPORD function. However, calculating Rp and Rs for each waveform is not at all clear. All my waveforms have a fundamental frequency between 1 and 10MHz so that the maximum value of the second harmonic is approximately 20MHz. Thanks in advance. Regards Calum Macdonald _____________________________________ Note: If you do a simple "reply" with your email client, only the author of this message will receive your answer. You need to do a "reply all" if you want your answer to be distributed to the entire group. _____________________________________ About this discussion group: To Join: To Post: To Leave: Archives: http://www.yahoogroups.com/group/matlab More DSP-Related Groups: http://www.dsprelated.com/groups.php3 ---------------------------------