# Filter Coefficient Design

Started by February 10, 2010
hi....
in my previous post i found w0 is not clear
sorry
so i'm 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.