filtering noise over 200kHz

[McMurray]

Hello!

I'm recording rat ultrasonic vocalizations at 1MS/s using a PCI-6132 DAQ.  A colleague of mine is analyzing the sonographic data from the recordings, and asked me to apply a filter to the signal as it's recorded.  The specifications he asked for was to "filter noise over 200kHs, with a reasonably steep slope".  I have no background in auditory analysis, so I have no idea what he's talking about, or how to impliment it.  Can anyone interpret this and help me figure this out?  Thanks!

Matt

[zenthoef · Accepted solution]

When I have been required to filter signals in LabVIEW, I have had success with the express VI called "Filter". You can find this in the following Palette: "Signal Processing -> Waveform Conditioning -> Filter.VI.

Before we get started, I noticed your requirement is to filter "noise over 200kHz". Does this mean filter everything over 200kHz or just "noise"?

If you are to filter everything over 200kHz, there are several parameters you will need to set to accomplish your goal. Double click on the Filter.VI once you have dropped it on the block diagram. The first thing you need to set is the fitler type. If you want to filter everything above 200kHz and pass everything below 200kHz, you want a lowpass filter. 

Since this is a low pass filter, you will only have one cutoff frequency. This is 200kHz is your case, since you want to pass everything below 200kHz. 

To get a steep slope, I like to use the elliptic topology. You can start with an order of 3 to see if this produces the response you need.

I'd recommend researching filters on a site like Wikipedia if this doesn't produce the outcome you need. Using this VI will get you where you need to go, but you may have to adjust the parameters based on your signal. However, I think this will at least get you started in the right direction!