From: rammya.tv on 9 Feb 2010 04:04 hi.... in my previous posy i found w0 is not clear so resending my queries again. i'm currently working on Analog Devices Dsp processor ADAU 1701.. Sigma studio is the software we are now on,in that i have some queries in the way they calculate filter coefficient.  main specification i needed to design a filter 1)Type[LPF,HPF, etc] 2)frequency 3)Q 4)Gain eg: I want a 2nd order LPF with Frequency= 1000 Q=0.5 Gain=1 The given below derivation is the one which i got from sigma studio help window. >w0 = 2*pi*f0/Fs >gainLinear = 10^(gain/20) >Lowpass >Transfer Function >H(s)=1/(s^2+(s/Q)+1) >Coefficients >alpha = sin(w0)/(2*Q) >a0 = 1 + alpha >a1 = 2*cos(w0) >a2 = 1  alpha >b0 = (1  cos(w0)) * gainLinear / 2 >b1 = 1  cos(w0) * gainLinear >b2 = (1  cos(w0)) * gainLinear / 2 After compiling we'll get coefficients a1,a2,b0,b1,b2 in hex format in CAPTURE WINDOW of software. i did manual calculation using the expression provided above and compare with that of coeffients of software, but it differs. Please help me to get detail calculation with the specification i given above. We know w0 = 2*pi*f0/Fs what is the value of pi(180 0r 3.14) w0 is the angular representation of requency i think it will be 180 then in above value of alpha will be zero always. it means Q doesnt have any importantce in filter design please suggest a good book which describe in detail about filter design with regards rammya

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