Applying high pass filter to streaming websocket data in javascript

Question

I'm using socket.io to stream data from a node.js server. The data is coming in at one packet every 33ms. I'm putting the data into a chart in real-time and I'd like to apply a digital high-pass filter on it.

I'm trying to figure out how to use DSP.js to apply an infinite impulse response algorithm on the data - high pass at 1hz - but I'm not really sure how to go about this.

I understand that I would create the filter object using this library (var filter = IIRFilter(HIGHPASS, 1, 30)), but as for the applying the filter (filter.process(signal)), I'm not sure what the signal would be. When each packet comes in, I add it to an array called data. Would it be on this array? Or would I have to do this for each packet as it comes in?

Answer 1

In an IIR filter, all past samples count in computation of the result for current sample. That's why it is called infinite impulse response.

I can see 2 options for your processing.

1. Wait, gather all the samples, finally do the processing before displaying the array data

2. Do it real-time! Keep in mind that the filtered data must not be mixed with raw data. Otherwise the filtering will be distorted. Create a new array filtered_data. Each time a packet comes in, copy it in data array, then copy data array in filtered_data and call filter.process(filtered_data). Finally display filtered_data.