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Thread: Basic FFT to identify frequency

  1. #1
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    Default Basic FFT to identify frequency

    For some reason the frequencies are off....

    package com.overdrive.FreqFinder;
     
    import java.nio.ByteBuffer;
    import java.nio.ByteOrder;
     
    import javax.sound.sampled.AudioFormat;
    import javax.sound.sampled.AudioSystem;
    import javax.sound.sampled.DataLine;
    import javax.sound.sampled.TargetDataLine;
     
    import org.apache.commons.math3.complex.Complex;
    import org.apache.commons.math3.transform.DftNormalization;
    import org.apache.commons.math3.transform.FastFourierTransformer;
    import org.apache.commons.math3.transform.TransformType;
     
    public class AudioInput {
     
    	TargetDataLine 	microphone;
     
    	final int 		audioFrames= 4096;  //power ^ 2
     
    	final float 	sampleRate= 8000.0f;
    	final int 		bitsPerRecord= 16;		// div 32768 ?
    	final int 		channels= 1;
    	final boolean 	bigEndian = true;
    	final boolean 	signed= true;
     
    	byte 			byteData[]; 	// length=audioFrames * 2
    	double 			doubleData[];	// length=audioFrames only reals needed for apache lib.
     
    	AudioFormat 	format;
     
     
    	public AudioInput () {
     
    		byteData= new byte[audioFrames * 2];  //two bytes per audio frame, 16 bits
     
    		//doubleData= new double[audioFrames * 2];  // real & imaginary
    		doubleData= new double[audioFrames];  // only real for apache
     
     
    		System.out.print("Microphone initialization\n");
    		format = new AudioFormat(sampleRate, bitsPerRecord, channels, signed, bigEndian);
    		DataLine.Info info = new DataLine.Info(TargetDataLine.class, format); // format is an AudioFormat object
     
    		if (!AudioSystem.isLineSupported(info)) {
    			System.err.print("isLineSupported failed");
    			System.exit(1);
    		}
     
    		try {
    			 microphone = (TargetDataLine) AudioSystem.getLine(info);
    		     microphone.open(format);
    		     System.out.print("Microphone opened with format: "+format.toString()+"\n");
    		     microphone.start();
    		}catch(Exception ex){
    			System.out.println("Microphone failed: "+ex.getMessage());
    			System.exit(1);
    		}
     
    	}
     
    	public int readPcm(){
     
    		int numBytesRead= 
    				microphone.read(byteData, 0, byteData.length);
    		if(numBytesRead!=byteData.length){
    			System.out.println("Warning: read less bytes than buffer size");
    			System.exit(1);
    		}
     
    		return numBytesRead;
    	}
     
     
    	public void byteToDouble(){
     
    		ByteBuffer buf= ByteBuffer.wrap(byteData);
    		buf.order(ByteOrder.BIG_ENDIAN);
    		int i=0; 
     
    		while(buf.remaining()>1){
    			short s = buf.getShort();
    			doubleData[ i ] = (new Short(s)).doubleValue() / 32768.0;
    			++i;
    		}
    	}
     
     
    	public void findFrequency(){
     
    		double frequency;
    		FastFourierTransformer transformer = new FastFourierTransformer(
    				DftNormalization.STANDARD);
     
    		Complex[] cmplx= transformer.transform(doubleData, TransformType.FORWARD);
     
    		double real;
    		double im;
    		double mag[] = new double[cmplx.length];
     
    		for(int i = 0; i < cmplx.length; i++){
                real = cmplx[i].getReal();
                im = cmplx[i].getImaginary();
                mag[i] = Math.sqrt((real * real) + (im*im));
            }
     
    		double peak = -1.0;
    		int index=-1;
            for(int i = 0; i < cmplx.length; i++){
                if(peak < mag[i]){
                    index=i;
                    peak= mag[i];
                }
            }
     
            frequency = (sampleRate * index) / audioFrames;
            System.out.print("Index: "+index+", Frequency: "+frequency+"\n");
     
    	}
     
    	public void printFreqs(){
    		for (int i=0; i<audioFrames; i++){
    			System.out.println("bin "+i+", freq: "+(sampleRate*i)/audioFrames);
    		}
    	}
     
     
     
    	public static void main(String[] args) {
    		AudioInput ai= new AudioInput();
     
     
    		int turns=10000;
     
    		while(turns-- > 0){
    			ai.readPcm();
    			ai.byteToDouble();
    			ai.findFrequency();
    		}
     
    		//ai.printFreqs();
    	}
    }


  2. #2
    Super Moderator jps's Avatar
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    Default Re: Basic FFT to identify frequency

    Welcome to the forum
    The frequencies are off?
    Crystal ball says you might be right. However since we have no idea what they should be perhaps you should explain much more what you mean by "the frequencies are off".
    What output are you getting? What did you expect?

  3. #3
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    Default Re: Basic FFT to identify frequency

    I can use a Piano or guitar to generate frequecies and use a tuner to check

  4. #4
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    Default Re: Basic FFT to identify frequency

    Please read: How to help yourself get help and try to explain your problem from the start.

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