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problem with coefficients when simulating Sigma first-order high pass

Question asked by dimitrisTymph on Aug 24, 2015
Latest reply on Aug 28, 2015 by KJBob



I am facing a problem with the coefficients of a first-order high pass filter in SigmaStudio.

I am trying to simulate the filter in Matlab.


In order to do so, I am using the formulas provided in the help of SigmaStudio, but it seems that the implementation that is suggested for the highpass filter there is not correct.



using the implementation when the gainLinear factor is 1 then apparently a1 = b0 and b1 = -b0.

However, this is not the case for a highpass filter of (for example) 1000 Hz cut-off frequency and a Gain of 0 as seen below.







It seems that the implementation is following the formulas:


b0 = (1+x)/2

b1 = -(1+x)/2

a1 = x


when I am using these formulas I get correct results in Matlab, and my results match (approximately) what I see in SigmaStudio.


Is this a mistake in the help file of SigmaStudio?


thank you,