# IIR filtering Doubt...

Started by March 28, 2002
 Hi everybody, Iam trying to do a filtering on a certain signal,lets say a sine wave consisting of three different frequency ranges ie, in real time my signal could consist of any 3 frequencies of the folllowing nature- 1] any one particular frequency in the range of 19-31hz 2] any one particular frequency in the range of 38-62hz 3]any one particular frequency in the range of 9.5-16.5hz (So,the maximum frequency is not more than 100hz...) like, say 25hz,40hz and 12hz and the next time it could be 30hz,50hz, 10hz so now, i want to design a passband iir elliptical filter to pass the 3 frequencies which will fall in these 3 ranges, but then my doubt is should i design 3 diffrent filters? or,is there anyway i can design a single passband filter which will take care of thise condition. The problem i face is that if design a pass-band filter of range 8hz-80hz(which covers all the 3 ranges i mentioned above...), then there is a chance it will then pass the frequencies say, 18hz and 32hz, if in case they are present!!! but then, thats an undesirable result for me... because as i see it, if i design a single filter of say, passband 5-60 hz then a frequency 32 might also get passed , which is unwanted for me... so what is the solution for such problems? has anybody faced such situtation before? any solutions on this? if i have to design 3 different filters, then how exactly to do it? can matlab help me to solve this problem? if so, how? the processor iam interested in implementing this tms320lf2407. regards, bhooshan