I have 2 serially connected multirate filters. One has 18 taps and the other has 61 taps. The decimation factors are 2, 2. Now I want to combine the 2 filters into one. The new coefficient file has 78 taps by using convolution. In FDAtool, the order is 137 after cascading. I think it is from 137=17+60*2 . So I guess I cannot just use convolution to combine 2 multirate filters. The problem is that the coefficients from FDAtool still shows in two sections, which stand for stage 1 (18 taps) and stage 2 (61 taps). Does anyone know how FDAtool expand the coefficients from 61 taps to 122 taps? Then I can do convolution on 18 and 122. This should be the key to solve the problem. Billy

# Combine 2 multirate filters

Started by ●March 17, 2006

Reply by ●March 17, 20062006-03-17

>I have 2 serially connected multirate filters. One has 18 taps and the >other has 61 taps. The decimation factors are 2, 2. Now I want tocombine>the 2 filters into one. The new coefficient file has 78 taps by using >convolution. In FDAtool, the order is 137 after cascading. I think it is >from 137=17+60*2 . So I guess I cannot just use convolution to combine 2 >multirate filters. > >The problem is that the coefficients from FDAtool still shows in two >sections, which stand for stage 1 (18 taps) and stage 2 (61 taps). Does >anyone know how FDAtool expand the coefficients from 61 taps to 122taps?>Then I can do convolution on 18 and 122. This should be the key to solve >the problem. > >Billy > >Okay, I am here again to answer my question. I put zeros between the taps and expanded the coefficient. It works well as I expected. I may need more theory to support it.