Prev: Filter coefficient calculation In Sigma studio
Next: Simulating Sample Jitter
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

 | 
Pages: 1
Prev: Filter coefficient calculation In Sigma studio
Next: Simulating Sample Jitter