Cannot Get Shelf Filter to Match

Hello Greg_Flanagan,

Could you please tell us about the revision of Sigmastudio that you are using?

If possible kindly attach your project and filter coefficients. So we will have a look and revert you.

Regards,

Harish

Hi Harishgowtham,

My version of Sigmastudio is Version 4.6. Build 0, Rev 1812 12/23/2020

In the attached project file I have the filter in question on the "woofer" channel.

Best regards,

GregRevo SS ADAU VCad testing sample rate.dspproj

See attached image. ADAU1466 response looks correct, compares exactly to the Matlab plot. Matlab:

[B,A] = designShelvingEQ(3.3,2.5,12920/(Fs/2),'hi');

Still not clear where the difference is.
If I calculate in MATLAB the High Shelf RBJ filter I get these coefficients:

% highShelf: H(s) = A * (A*s^2 + (sqrt(A)/Q)*s + 1)/(s^2 + (sqrt(A)/Q)*s + A)

HIGH SHELF RBJ @ 12920.0 Hz & Q = 2.5 & 3.3 dB Gain

1.1852

0.0519

0.7889

1.0000

0.3542

0.6719

If I then import the table to SigmaStudio and measure the electrical transfer function I get a response the same as my MATLAB calculation.

If I use the filter block as in your above example I get a different response (white curve in below plot)

Is maybe your "designShelvingEQ" formula different than the RBJ formula?
Below is from the general filters documentation page:

Best regards,

Greg

Hello,

Looks like the confusion is using Slope vs. Q. The SigmaStudio module is using Slope=2.5 notQ, so the Q = 1/sqrt((A+1/A)*(1/Slope-1)+2) = 1.13 where A=10^(dbgain/40), dbgain=3.3

Note that, for Slope=1, Q=0.707

For Q=2.5 you need a Slope=10.4, see attached image

Thanks for the clarification. That seems to be it!