May 29 2017

OpenFrameworks FFT

Following on from the first experiment in OpenFrameworks a visualization using FFT and SoundPlayer.  FFT is not difficult to utilize in relation to ofSoundPlayer class - the magnitude of frequency bands are returned in the ofSoundGetSpectrum () "global function".  If one wishes to implement FFTs in relation to live audio input or using ofSoundStream class it can be done - however it is not so painless. 

As a starting point for the visual component I made use of the same class "Flow" that was used in the envelope test.  This class allowed the construction of various objects each allotted a separate "bin" from the sound spectrum.  The advantage of using FFT's over some kind of peak amplitude analysis is the control. The different objects on the picture plane can be controlled through frequency ranges.  This is not very fine grained in the present example.  There are ways to make transforms more sophisticated in connection to the actual "notes" that are appearing in a .wav or an audio input.  In the present case however the coarse-grained approach was the one taken up.

Some of the code utilized in the work will be produced below.  There is nothing too complicated there however.  The difficult thing is to work out which ways to scale the different objects (in relation to size, color etc.) with the incoming spectrum information.  Of course most of the information that is utilizable (insofar as it connects to frequency bins that one is actually hearing) is in the first series of bins.   

void ofApp::draw(){

    ofBackground(0);

    float *val = ofSoundGetSpectrum( N );

    for (int i = flows.size()-1; i >=0; i--) {

        float rf=flows[i].spectrum[i+1] *((i*20)*2);

        float rg=flows[i].spectrum[i+1] *((i*5)*50);

        float rb=flows[i].spectrum[i+1] *((i+50)+(i*10));

        float ra=flows[i].spectrum[i+1] *((i+50)+(i*2));

        ofSetColor((int)rf%255,(int)rg%255,(int)rb%255, (int)ra%255);

        //printf("%d \n",(int)rf);

        flows[i].draw();

        for ( int j=0; j<N; j++ ) {

            flows[i].spectrum[j] *= 0.97; 

            flows[i].spectrum[j] = max( flows[i].spectrum[j], val[j] );

            flows[i].twistY = ofMap( flows[i].spectrum[ flows[i].bandRadz[i] ], 1, 3, ofRandom(100),ofRandom(400), true );

            flows[i].countX = ofMap(flows[i]. spectrum[ flows[i].bandVel ], 0, 1, 1, 250 );

        }

    }

}