Obtaining Sound Pressure Level of wav file

Question

I am trying to obtain and represent the SPL of a a wav file previously recorded with the internal mic of my device. The problem is that the values that I am getting seem not to be logic at all, as I´m getting values over 100 db simply clapping my hands as you can see here:

_{(source: subirimagenes.com)}

This is what I am doing:

First of all, as the wav file is saved in 16-bit PCM, I operate with its bytes to have an unique double value normalized between [-1,1] ( I don´t operate with the first 44 bytes as it is the wav header).
Then, following this equation SPL=10*log(audioSample/Iref) I obtain each of the desired sound levels (being Iref=10^-12).
At the end I calculate the max and min values to set the margins of the plot.

Do you guys know what Im I doing wrong? I think the values should be around half of the ones obtained

Here is the piece of code:

protected void miThread() {
          Thread t=new Thread()  {
            public void run(){
            //Operaciones ope=new Operaciones();
            double [] st =new double [arr.length];
             int j=0;
                try{
                  for (int i = 44; i < s; i+=2) {
                    // convert byte pair to int
                    double audioSample = (double) (array[i+1] << 8 | array[i] & 0xff)/ 32767.0;

                    arr[j]=audioSample;  //double
                    n[j] = (Number)arr[j];  //Number

                    st[j]=10*Math.log10(Math.abs((audioSample/Math.pow(10, -12)))); //double
                    l[j]=(Number)(10*Math.log10(Math.abs((audioSample/Math.pow(10, -12)))));  //Number

                    if(audioSample == 0.0 ){
                        if(j!=0){
                        l[j]=l[j-1];
                        st[j]=st[j-1];
                        }else{
                            l[j]=0.0;
                            st[j]=0.0;
                        }
                      }

                    j=j+1;}
                    min=Operaciones.minimum(arr);
                    max=Operaciones.maximum(arr);
                    min2=Operaciones.minimum(st);
                    max2=Operaciones.maximum(st);
                    }
                    catch (NullPointerException e){
                        e.printStackTrace();
                        } 
                handle.post(proceso);
               } }; t.start();                  
                }

        final Runnable proceso=new Runnable(){
            public void run(){
                //plot.redraw();
                //plot2.redraw();
                Toast.makeText(Grafica.this, 
                "Ya se ha cargado todo el array", Toast.LENGTH_LONG).show();
            }
        };

Obtaining Sound Pressure Level of wav file

Answers (1)

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