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Forum: DSP Extracting filter coefficients from fdatool IIR filter object


von Jefazo J. (jefazo92)


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Hi everyone,

I have designed an IRR filter in fdatool but since I can't export the 
coefficients as a vector into the workspace, I exported the filter as an 
object. The problem is that when I open the object, I have 3 arrays 
stored in it (ScaleValues, States and sosMatrix). Please, could someone 
exlplain me the difference between each array and, more importantly, how 
I can extract the filter coefficients from my IRR filter ? Also if you 
could write down links to official sources/documentation, it would 
amazing. Please any help would be really appreciated. Thank you in 
advance.

P.S. I am converting my structure to Direct-Form 1since, supposedly, it 
gives the coefficients for the ideal IRR filter or is, at least, more 
accurate but I am also not sure about it and if soemone could also 
explain me what it is exactly, it would be greatly appreciated.

Also, I am using a Lowpass Chebyshev Type II filter for my IIR. Thank 
you.

von Joe F. (easylife)


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I'm not a mathlab user but looking at this

https://www.mathworks.com/help/signal/ref/sos2tf.html

leads me to the assumption that "sos" stands for "second-order section" 
and is an n x 6 array containing the IIR coefficients.

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