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How get eq coefficent to write sigma dsp ?

Question asked by walkercc on May 10, 2011
Latest reply on May 11, 2011 by BrettG

How convert it?

Eq coefficent write to sigma dsp have 5 cofficent,


for example,  like help file's formula, calculate peaking eq coefficent,  my code is :
    double omegac= 2.0 * pi * F/G_FS;
    double cosv= cos(omegac);
    double alpha= sin(omegac) / (2.0 * Q);
    double A= pow(10, G/40);
    double gainLinear = pow(10, lg/20);

    double a0 = 1.0 + alpha/A;
    double a1 = -2.0 * cosv;
    double a2 = 1.0 - alpha/A;
    double b0 = (1.0 + alpha*A )*gainLinear;
    double b1 = -(2.0 * cosv) * gainLinear;
    double b2 = (1.0 - alpha*A ) * gainLinear;

 

and Sigmastudio help file said "all the coefficients are divided by a0,
normalizing them and making a0 = 1, so that only 5 coefficients must be stored."

 

So, 5 coeff is :
double a1a0 = a1/a0;
double a2a0 = a2/a0;
double b0a0 = b0/a0;
double b1a0 = b1/a0;
double b2a0 = b2/a0;

 

It's my solution, but compare sigma dsp decimal val and my result, is differnet!
i don't know wha's wrong ?  example: F = 31Hz Fs = 48k Q = 1.41 Boost = 1.0

 

my result is :

 

123.jpg

sigmastudio result ( 5 coefficent is below):

1234.jpg


Last, the help file said"a1 and a2 need to be inverted", what's meaning?

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