EVAL-AD1954EB Analog Devices Inc, EVAL-AD1954EB Datasheet - Page 32

• Manufacturer Part Number: EVAL-AD1954EB
• Description: BOARD EVAL FOR AD1954
• Manufacturer: Analog Devices Inc

Specifications of EVAL-AD1954EB

• Rohs Status: RoHS non-compliant

APPENDIX
Cookbook Formulae for Audio EQ Biquad Coefficients
(Adapted from Robert Bristow-Johnson’s Internet Posting)
For designing a parametric EQ, follow the steps below.
1. Given:
2. Compute intermediate variables:
AD1954
A = 10
Frequency
Q
dB_Gain
Sample_Rate
 = 2    Frequency/Sample_Rate
sn = sin()
cs = cos()
 = sn/(2  Q)
(dB_Gain/40)
–32–
3. Compute coefficients:
4. The transfer function implemented by the AD1954 is given by:
Y(n) = a1  y(n – 1) + a2  y(n – 2) + b0  x(n)
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))
H(Z) = (b0 + b1  Z – 1 + b2  Z – 2)/
Note the inversion in sign of a1 and a2 relative to the more
standard form. This form is used in this document because
the AD1954 implements the difference equation using the
formula below.
+ b1  x(n – 1) + b2  x(n – 2)
(1 – a1  Z – 1 – a2  Z – 2)
REV. A