AD1954 Analog Devices, AD1954 Datasheet - Page 34

• Manufacturer Part Number: AD1954
• Description: SigmaDSP Digital Audio Processor
• Manufacturer: Analog Devices

AD1954
APPENDIX
Cookbook Formulae for Audio EQ Biquad Coefficients
(adapted from Robert Bistro-Johnsons Internet posting)
For designing a Parametric EQ, follow the steps below.
1. Given:
2. Compute Intermediate Variables
3. Compute Coefficients
4. The transfer function implemented by the AD1954 is given by:
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.
Y(n) = a1
Frequency
Q
dB_Gain
sample_rate
A = 10^(dB_Gain/40)
omega = 2
sn = sin(omega)
cs = cos(omega)
alpha = sn/(2
b0 = (1 + A
b1 = –2
b2 = (1 – (alpha/A))/(1 + (alpha/A))
a1 = 2
a2 = –(1 – (alpha/A))/(1 + (alpha/A))
H(Z) = (b0 + b1
×
×
×
cs/(1 + (alpha/A)) = –b1
y(n–1) + a2
cs/(1 + (alpha/A))
×
×
π
×
alpha)/(1 + (alpha/A))
×
Q)
Frequency/Sample_Rate
×
Z–1 + b2
×
y(n–2) + b0
PRELIMINARY TECHNICAL DATA
×
Z–2)/(1 – a1
×
x(n) + b1
×
Z–1 – a2
×
x(n–1) + b2
×
Z –2)
×
x(n–2)