Hi

at first i should describ our design for you ,we want to design a system and the block crossover is used as the high order LP filter, Our DSP prossesor is controled by extern microcontrolor ,So the coefficient value must be calculated by extern microcontrolor according to the formula and the controlor send the corresponding value to DSP prosseeor come true controling.

Now we meet problem :

1 for high order filter different order,the number of coefficient is defferent,for example bessel 12 dB have 5 coefficient , bessel 18 dB have 8 coefficient ,

bessel 24 dB have 10 coefficient ,and so on !

2 we don't know the equationt of the coefficient.

before somebody tell me the high order filter is simply serialized by general 2nd order filter and general 1st order filter ,and there is the equation in help file .

but after much experiment i find the the value of coefficient i get from equation is not correspond to which i get from the SigmaStudio,

for example ,general 2nd order filter,frequency=1000HZ;Q=1.41,Fs=48000;gain=0;

below is the data i get from experiment

The data get from the equation of help file :

a0=1.0008101520074285072310965239913;

a1=-1.9999947804650706869450798840089;1 /a1=-0.50000130488713778026095773346491;

a2=0.999189847992571492768903476009; 1/a2=1.0008108088858750397659847761385;

b0=--0.0000013048837323282637300289978;

b1=-0.000002609767464656527460057994;

b2=b0;

The data get from SigmaStudio:

EQ1940Single10B1=0.00408828258514404;

EQ1940Single11B1=0.00817668437957764;

EQ1940Single12B1=0.00408828258514404;

EQ1940Single11A1=1.8951700925827;

EQ1940Single12A1=-0.911523461341858;

We could find the difference from the data,if you know please reply soon!

I 'm look forward to your reply ! thanks

Page 8 in the PDF shows the calculations for "higher order" low pass and high pass Butterworth filters. Use those equations, and substitute your values in for

orderindexandi, both of which appear in the calculations.Filt1 is the first cascaded filter, and Filt2 is the second cascaded filter (and so on...).

You seem to be using Butterworth 24 in your crossover. From the PDF, page 9, you can see that a Butterworth 24 filter consists of two higher order Butterworth filters, cascaded. That's why you see two groups of coefficients (one for each filter).