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Using butterworth filter for reducing noise

Hi! Im having a problem in putting a butterworth filter (bandpass type) on my acquired data. Im using the filter to reduce the background noise.  I think there is a misplacement of the filter since the output of the filter is connected to a SVL scale voltage to EU vi. I need a scale because the data must be presented in SPL(dB) vs Frequency. The error occurs at the power VI which states that the number of samples/ sampling frequency must be greater than 0. Without the filter, the program runs fine but the data acquired and presented in SPL vs freq is quite noisy. My concern is that where do i place the filter? Is this possible that the output of the filter can be inputted to the SVL scale voltage to EU vi? Attach is a photo of the program and the VI.  The frequency I need to acquire ranges from 140Hz to 18KHz.

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Two problems with trying your VI: I do not have the Sound & Vibration Toolkit so two VIs are missing. I do not have your hardware so I cannot acquire any data.

 

Put an indicator on the array wire at the input to the filter. Run your VI so that data is present. Then Make Current Values Default and save. Post that VI.

 

Have you placed indicators or probes on the outputs of the filter and scaling VIs to see whether any data is present and waht it looks like? Do you get any errors? The filter VI has an error output but it only returns an error code, not the full error cluster. Automatic error handling (if you have it turned on) will not catch those errors. You need to wire an indicator or Error Cluster from Error Code.vi to see if there is an error.

 

Often errors like that are from not setting the filter parameters correctly.

 

Lynn

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