o/p of butterworth filter and o/p of butterworthcoeff->cascade coeff->IIR filter is different?

[PSADSP]

Hello All,

I am designing a system wherein i need to make use of a IIR butterworth Low pass filter .

I tried implementing the same in Labview using 2 methods:

1st method:

Selected Signal processing-->Filters-->ButterworthFilter.vi

Got the o/p.... attached image 1--> Waveform

2nd method:

Selected Signal processing-->Filters--> Advanced IIR filter-->ButterworthCoefficients.vi-->CascadetoDirectCoefficients.vi -->IIRfilter.vi

Got the o/p...attached image 1--> Waveform Cascade Coefii

Both the o/ps differ from in each other if you apply for order 5, LPF, cut off: 35...samples : 250000....

Could you please let me know what difference is there in selecting either of the filter designing way.....

Please reply back asap as im stuck here and am confused....also im new to signal processing....so not sure abt the error im making...

Thanks in advance...

PSADSP

[RLSSpeedy]

Afternoon PSADSP,

I would dare to say it is possibly your implementation of these VI's that is giving you a difference in your results. The "Butterworth Filter.VI" uses the "Butterworth Coefficients.VI" and the "IIR Cascade Filter.VI" as sub vi's to do its thing.

Have another look at there VI's and post back if you still having issues.

regards

Richard