a question about EQ Algorithm
In the sigmastudio help document, it says as follows:
"The 2nd Order and medium-size EQ blocks use multiple biquad filters, based on Robert Bristow-Johnson's work as shown here:
Common Variables
A = 10^(boost/40)
ω0 = 2*pi*f0/Fs
alpha = sin(ω0)/(2*Q) (type: Peaking)
= sin(ω0)/2 * sqrt((A + 1/A)*(1/S - 1) + 2) (type: Shelving) "
What does the variable "S" mean in the equation above? I did't find the definition about "S" before this equation. There are all the definition about the intermediate variables, like A, ω0, and alpha, but "S".
Would you like to tell me the definition about "S" here, or something else ? Thanks a lot!
And how can i get "s"? I found the definition in the paper "cookbook formulae for audio equalizer biquad filter coefficients" by
Robert Bristow-Johnson's.
But it is somewhat indistinct to get the variable "S" from the known variables, boost, gain, Q, fc/fs.
Accoding to the paper, whether should I adjust the two variables ,boost, and Q , to locate the "point"--S=1, which is the steepest shelf slope and remain monotonically increasing or decreasing gain with frequency, and then compare the current shelf slope to the steepest one , then get the variable "s" at last ?
Please give me a detailed reply. Thanks a lot.
Hello,
Perhaps this thread will help (scroll down a ways):
Best regards,
Bob
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