Filtering Function IIR Fiilter - Biquad Filter

[fohrer]

Posted on July 28, 2014 at 11:46

Hi everyone,

I have to design an IIR Filter and i want to use the DSP library provided. I'm new to digital filtering and i want some help to understand the biquad function in the library. I found an exemple in the arm_graphic_equalizer_exemple_q31 in the DSP Lib. I'm using MATLAB to design my filter with FDA Tool, but still it seems to generate different

My questions are : 

- How can I generate coeficients with MATLAB to be use in the Biquad cascad filter.

- Any help about understanding the Biquad function, or can soemone provide me an easy  example of using it.

Sorry about my bad English

Thank you in advance,

Luc

#digital-filter-iir-biquad

[zeros_and_ones1991]

Posted on July 29, 2014 at 15:47

Well Luc , Biquad filter is simply a second order filter , meaning  the denominator will always be in the form (S^2+aS+b) , but the numerator will differ according to the type of filter u would want (LP , HP , BP , or BS) . To be honest I have not heard of the word ''Biquad'' in the Digital Filtering , only in analog designs , but speaking of Digital filters , u would use FIR or IIR . I used Window Function approach to design Digital Filter . First you choose a Window function (in the Frequency Domain) , say a simple gate (or rectangular) , limited by the cut off frequency , then you get the Frequency Domain expression , then get the inverse FT , then implement the resulting function (Time Domain) as the filtering function .

Good Luck

[fohrer]

Posted on July 30, 2014 at 13:44

Hi,

Thank you for your response and your advices.

I want to design some BP IIR filters. It's ok now i found a solution to calculate the coefficients for using the function arm_biquad_cascade_df1_init_q31 provided in the DSP library. I'm using MATLAB to design my filter and export de SOS martrix.

Thank's a lot for your time