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A Question encountered in IIR filter design

Question asked by Jingchang on Sep 23, 2013
Latest reply on Sep 23, 2013 by BrettG

ExperimentWe design an IIR filter in Matlabthen the filter is transplanted to SigmastudioHowever the Magnitude Responses obtained by Matlab and Sigmastudio are differentWhy

The Detailed operations are as following.

Step 1Define the characteristics of IIR filter in Matlab as 4 order, 1024 sampling rate, 300Hz frequency-pass and 400Hz frequency-stop.

Fig1.bmp

Figure 1

Step 2:The magnitude response obtained in Matlab as Figure 2.

Fig2.bmp

Figure 2

     Though observing the figure 2,we find that the obtained magnitude response is consistent with the characteristics defined in Step 1.

 

Step 3: Export the coefficients from the Matlab。

Fig3.bmp 

图3

Step 4: Design the program in Sigmastudio,as figure 4.

  Fig4.bmp

Figure 4

Step 5:Import the coefficients (obtained in Step 3) into the IIR filter of Sigmastudio.

Fig5.bmp 

Figure 5

Step 6. The magnitude response obtained by SigmaStudio is as Figure 6 shown.

Fig6.bmp 

Figure 6

  The coefficients used by Sigmastudio and Matlab are the same,however the obtained magnitude response figures are different. Why? Could you explain it detail.

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