Bw_CascadeCoef upper_cutoff_frequency

[wlattery]

In the function Bw_CascadeCoef, is the 'upper_cutoff_frequency' parameter ignored if the IIR Filter is set to a highpass filter?

[Kurt-P]

The function is most likely set to zero in that situation since that is a not a parameter that is used by the mathmatical equations to create an IIR filter. Are you seeing any error or strange behavior?

-KP

[wlattery]

Here is a sample of my code:

#define LOW_CUTOFF_5Hz_HP   5.0 

#define HIGH_CUTOFF_5Hz_HP  100000.0 

#define FILT_TYPE_5Hz_HP        1 
#define FILT_ORDER_5Hz_HP     3

IIRFilterPtr  filtStruct_5Hz_HP;

filtStruct_5Hz_HP = AllocIIRFilterPtr (FILT_TYPE_5Hz_HP, FILT_ORDER_5Hz_HP);

Bw_CascadeCoef (daqSampRate, LOW_CUTOFF_5Hz_HP, HIGH_CUTOFF_5Hz_HP, filtStruct_5Hz_HP);

I don't have an error, but just wanted to confirm with NI that the parameter for the High Frequency Cutoff is irrelevant when using a High Pass Butterworth filter.

[Kurt-P]

Yes, that high frequency parameter is ignored. There is an example that you can try called IIfiltr.cws located in the directory:

C:\Users\Public\Documents\National Instruments\CVI2013\samples\analysis

When you change the high cutoff frequency parameter on the user interface, the filter does not change.

-KP