Plotting DSP System Response Curve
We're developing a solution for a client, of which one of the requirements is to be able to change the filter value settings and save the new response to the device. The problem we're having is with plotting the curve in the user interface we're building. For peaking filters the boost/cut level seems to vary with frequency. We thought that this may have been an issue with our plotting method however simulated response curves in SigmaStudio demonstrate the same problem. Is this frequency dependant response variation inherent of RBJ filters or, is it an issue with the algorithm used for drawing the response curve?
(The attached images show this problem clearly. Note the filter settings at the bottom of each image.)
Just from looking at this I'm guessing it could be a plot problem. Have you tried to implement it? Does the amplitude vary there also? Is there a double precision version that works any differently?
The filters used are the double precision Text-In Filters. I'm away over the next two weeks and will be testing the actual implimentation on the hardware when I return.
Hi,
This is indeed a plot problem. The precision of the drawing function (which I believe is inherited straight from .NET) seems to be limited. If you actually measure the frequency response you'll see that the levels match your expectations.
If your measurements still show a discrepancy, please post those here.
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Thank you,
EZ Admin
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