Forum Discussion
Altera_Forum
Honored Contributor
Honored Contributorhalf-band filter
I am trying to implement a half-band filter in Verilog. The questions are: 1. what is the definition for a half-band filter? Is it the same as what we have in traditional multi-rate DSP "P(z)+P(-z)=c...
Altera_ForumHonored Contributor
Honored Contributor --- Quote Start --- Should a half band filter satisfy P(z)+P(-z)=constant (or P(w)+P(w+pi)=constant) if P(z) is a half band filter? However, in the example http://www.dsprelated.com/showarticle/124.php, this sum is very small around pi/2 compared to its value at 0, pi, 2*pi. Besides, the value also alternates between positive and negative. Is there a problem here? --- Quote End --- The filter given in that example is this: h = [-8,0,27,0, -68,0,146,0,-281,0,499,0,-37,0,1353,0,-2161,0,3547,0,-6561,0,20727,32768,20727,0 -6561,0,3547,0,-2161,0,1353,0,-37,0,499,0,-427,0,-68,0,27,0,-8] the passband ripple is about 1 dB and this too bad for a 45 taps (unless there is typing error by them or me) Otherwise it does cutoff at half Nyquist What are those (P) rules you mentioned and from where did you get them? If you have matlab you can use firnyquist function or firhalfband or even fir1 setting cutoff to .5 and odd filter It is also possible to design IIR halfband but this not that popular.
