Hello,

I'm a Belgian engineering student currently in the proces of writing an  java application that transforms the line input of a soundcard into an osciloscope. For everything input related i'm using Processing and Minim as a component in the application.

I've got the drawing of the signal working, but i'm currently experiencing problems with determining the frequency of the input signal (i'm using an ipod with a 1k Hz MP3 file on it).

I've tried two seperate things:

I've tried to use timers to determine the period of the signal, but this returns rubbish values which start large and slowly converge to zero. I suppose this is due to noise. 

2. public void draw()
3. {
4.   background(255);
5.   stroke(0);
6.   
7.   line(0,300,800,300);
8.   
9.   // draws waveform and calculates the period in real time by measuring the time it takes to complete one cycle in milliseconds
10.    for(int i = 0; i < in.bufferSize() - 1; i++)
11.    {
12.    line(i, 300 + in.left.get(i)*200, i+1, 300 + in.left.get(i+1)*200);
13.     
14.    //period calculation
15.    if (in.left.get(i) * in.left.get(i+1) <= 0 && firstRoot == false ) //tests whether the first root has been passed
16.    {
17.    beginTime = System.nanoTime(); //stores the time the first root has been passed
18.    firstRoot  = true; // first root has been passed
19.    }
20.    else if (in.left.get(i) * in.left.get(i+1) <= 0 && secondRoot == false) // tests whether the second root has been passed
21.    {
22.    secondRoot = true; //second root has been passed
23.    }
24.    else if (in.left.get(i) * in.left.get(i+1) <=0 && secondRoot == true) // tests whether the third root has been passed
25.    {
26.    nanoperiod = System.nanoTime() - beginTime; //determines the time it took to complete the cycle
27.    System.out.println(nanoperiod/1000000000.0); //convert to second and print to Console #DEBUG
28.    secondRoot = false; // reset the second root
29.    beginTime = System.currentTimeMillis(); //reset begintime
30.    }
31.    }
32. }

I'm currently trying to use FFT to determine the frequency of the signal, but i'm having troubles getting both the drawing and the FFT in the same loop. The way i see it i need to have two For() loops running at the same time iterating over two different things. i'm currently reading up on multithreading in java but i doubt this will solve my problem.