PreprocessingModulesExamples/HighPassFilterExample/HighPassFilterExample.cpp

/*
 GRT MIT License
 Copyright (c) <2012> <Nicholas Gillian, Media Lab, MIT>
 
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 */

/*
 GRT HighPassFilter Example
 This example demonstrates how to create and use the GRT HighPassFilter PreProcessing Module.
 
 The HighPassFilter implements a first-order infinite-impulse-response (IIR) high pass filter. 
 
 In this example we create an instance of a HighPassFilter and use this to filter some
 dummy data, generated from a series of sine waves (with increasing frequency ranging from 0.1Hz to 8Hz). 
 The test signal and filtered signals are then printed to std::cout.
 
 This example shows you how to:
 - Create a new HighPassFilter instance a 1 dimensional signal
 - Set a specific filter cutoff frequency
 - Filter some data using the HighPassFilter
 - Save the HighPassFilter settings to a file
 - Load the HighPassFilter settings from a file
*/

//You might need to set the specific path of the GRT header relative to your project
#include <GRT/GRT.h>
using namespace GRT;
using namespace std;

int main (int argc, const char * argv[])
{
 //Create a new instance of a high pass filter, using the default constructor
 HighPassFilter hpf;
 
 //Set the cutoff frequency of the filter to 2.0Hz
 hpf.setCutoffFrequency( 2, 1.0/1000.0);
 
 //Create some varaibles to help generate the signal data
 const UINT numSeconds = 60; //The number of seconds of data we want to generate
 double t = 0; //This keeps track of the time
 double tStep = 1.0/1000.0; //This is how much the time will be updated at each iteration in the for loop
 double freq = 0; //Stores the frequency
 map< UINT, double > freqRates; //Holds the frequency rates
 map< UINT, double >::iterator iter; //An iterator for the frequency rates map
 
 //Add the freq rates
 //The first value is the time in seconds and the second value is the frequency that should be set at that time
 freqRates[ 0 ] = 0.1;
 freqRates[ 10 ] = 0.5;
 freqRates[ 20 ] = 1;
 freqRates[ 30 ] = 2;
 freqRates[ 40 ] = 4;
 freqRates[ 50 ] = 8;
 
 //Generate the signal and filter the data
 for(UINT i=0; i<numSeconds*1000; i++){
 
 //Check to see if we should update the freq rate to the next value
 iter = freqRates.find( i/1000 );
 if( iter != freqRates.end() ){
 //Set the new frequency value
 freq = iter->second;
 }
 
 //Generate the signal
 double signal = sin( t * TWO_PI*freq );
 
 //Filter the signal
 double filteredValue = hpf.filter( signal );
 
 //Print the signal and the filtered data
 cout << signal << "\t" << filteredValue << endl;
 
 //Update the t
 t += tStep;
 }
 
 //Save the HighPassFilter settings to a file
 hpf.save("HighPassFilterSettings.grt");
 
 //We can then load the settings later if needed
 hpf.load("HighPassFilterSettings.grt");
 
 return EXIT_SUCCESS;
}