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I was able to wrote a program for capturing an audio signal, remove background noise, applying window function and visualisation that signal. My program is working up to this point without an error. Now I am trying to implement a High Pass filter to my code. I have already found a API for this part. But I was unable to apply it according to my code. Here is my code :

private class RecordAudio extends AsyncTask<Void, double[], Void> {
    @Override
    protected Void doInBackground(Void... params) {
        started = true;
        try {
            DataOutputStream dos = new DataOutputStream(
                    new BufferedOutputStream(new FileOutputStream(
                            recordingFile)));
            int bufferSize = AudioRecord.getMinBufferSize(frequency,
                    channelConfiguration, audioEncoding);
            audioRecord = new AudioRecord(MediaRecorder.AudioSource.MIC,
                    frequency, channelConfiguration, audioEncoding,
                    bufferSize);

            NoiseSuppressor.create(audioRecord.getAudioSessionId());
            short[] buffer = new short[blockSize];
            double[] toTransform = new double[blockSize];
            long t = System.currentTimeMillis();
            long end = t + 15000;
            audioRecord.startRecording();

            while (started && System.currentTimeMillis() < end) {
                int bufferReadResult = audioRecord.read(buffer, 0,
                        blockSize);
                for (int i = 0; i < blockSize && i < bufferReadResult; i++) {
                    toTransform[i] = (double) buffer[i] / 32768.0;
                    dos.writeShort(buffer[i]);
                }
                toTransform = hann(toTransform);
                transformer.ft(toTransform);
                publishProgress(toTransform);
            } 
            audioRecord.stop();
            dos.close();
        } catch (Throwable t) {
            Log.e("AudioRecord", "Recording Failed");
        }
        return null;
    }

This is the API link.

Can anyone help me to do this function? I would really appreciate it! :)

Thanks in advance!

Hash_S
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    You asked the [same question][1] 3 days ago. [1]: http://stackoverflow.com/questions/28252665/how-to-implement-a-high-pass-filter-for-an-audio-signal – Jens Feb 03 '15 at 20:48
  • @Jens yes. I posted it again because it was not helped me. Anyway yesterday night I was able to implemented high pass filter function. So what do I need to do ?? Do I need to close this question? Because I am new to stackoverflow. – Hash_S Feb 04 '15 at 03:18
  • Normally you would add a comment to the response to your first question, clarifying why the response does not answer your question. Maybe rephrase (edit) your original question to improve the readability. Remember that StackOverflow users keep reading these questions a long time after they were posed. – Jens Feb 04 '15 at 07:30

1 Answers1

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here is the class I convert to java from a library I found in c#. I use it and it work great. you can use this class for low pass filter too

public class Filter {


/// <summary>
/// rez amount, from sqrt(2) to ~ 0.1
/// </summary>
private float resonance;

private float frequency;
private int sampleRate;
private PassType passType;


public float value;

private float c, a1, a2, a3, b1, b2;

/// <summary>
/// Array of input values, latest are in front
/// </summary>
private float[] inputHistory = new float[2];

/// <summary>
/// Array of output values, latest are in front
/// </summary>
private float[] outputHistory = new float[3];

public Filter(float frequency, int sampleRate, PassType passType, float resonance)
{
    this.resonance = resonance;
    this.frequency = frequency;
    this.sampleRate = sampleRate;
    this.passType = passType;

    switch (passType)
    {
        case Lowpass:
            c = 1.0f / (float)Math.tan(Math.PI * frequency / sampleRate);
            a1 = 1.0f / (1.0f + resonance * c + c * c);
            a2 = 2f * a1;
            a3 = a1;
            b1 = 2.0f * (1.0f - c * c) * a1;
            b2 = (1.0f - resonance * c + c * c) * a1;
            break;
        case Highpass:
            c = (float)Math.tan(Math.PI * frequency / sampleRate);
            a1 = 1.0f / (1.0f + resonance * c + c * c);
            a2 = -2f * a1;
            a3 = a1;
            b1 = 2.0f * (c * c - 1.0f) * a1;
            b2 = (1.0f - resonance * c + c * c) * a1;
            break;
    }
}

public enum PassType
{
    Highpass,
    Lowpass,
}

public void Update(float newInput)
{
    float newOutput = a1 * newInput + a2 * this.inputHistory[0] + a3 * this.inputHistory[1] - b1 * this.outputHistory[0] - b2 * this.outputHistory[1];

    this.inputHistory[1] = this.inputHistory[0];
    this.inputHistory[0] = newInput;

    this.outputHistory[2] = this.outputHistory[1];
    this.outputHistory[1] = this.outputHistory[0];
    this.outputHistory[0] = newOutput;
}


public float getValue()
{
    return this.outputHistory[0];
}


}

and this is how I use this 

    Filter filter = new Filter(15000,44100, Filter.PassType.Highpass,1);
    for (int i = 0; i < numSamples; i++)
    {
        filter.Update(floatArray[i]);
        floatArray[i] = filter.getValue();
    }

after you got floatArray's fft, you see it is filtered. Hope it helps

smoothumut
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