3. Compute coefficients:
Cookbook Formulae for Audio EQ Biquad Coefficients
(Adapted from Robert Bristow-Johnson’s Internet Posting)
b0 = ( 1 + A )/( 1 + (/A))
b1 = –2
cs/( 1 + (/A)) b2 = (1 – ( A))/(1 + (/A))
a1 = 2
cs/(1 + (/A)) = –b1 a2 = –( 1 – (/A))/( 1 + (/A))
For designing a parametric EQ, follow the steps below.
Frequency
Q
4. The transfer function implemented by the AD1954 is given by:
H(Z) = (b0 + b1 Z – 1 + b2
Z – 2)/
(1 – a1 Z – 1 – a2
Z – 2)
dB_Gain
Sample_Rate
Note the inversion in sign of a1 and a2 relative to the more
standard form
.
T
his form is used in this document because
the AD1954 implements the difference equation using the
2. Compute intermediate variables:
= 2
Frequency/Sample_Rate Y(n) = a1 y(n – 1) + a2 y(n – 2) + b0 x(n)
+ b1
x(n – 1) + b2 x(n – 2) REV. A
ADI [ ADI ]
