Performing dtmf-decoder FFT on sound file android

Question

I am using this FFT library to perform the FFT on the sound caught by device microphone. I am using following code:

int bufferSize = AudioRecord.getMinBufferSize(frequency,
                    channelConfiguration, audioEncoding);
            AudioRecord audioRecord = new AudioRecord(MediaRecorder.AudioSource.DEFAULT,
                    frequency, channelConfiguration, audioEncoding, bufferSize);
            int bufferReadResult;

            try {
                audioRecord.startRecording();
            } catch (IllegalStateException e) {
                e.printStackTrace();
                Log.e("Recording failed", e.toString());
            }
            while (true) {
                bufferReadResult = audioRecord.read(buffer, 0, blockSize);
                if (isCancelled())
                    break;
                boolean bln = false;
                for (int i = 0; i < blockSize && i < bufferReadResult; i++) {
                    toTransform[i] = (double) buffer[i] / 32768.0;
                    if (buffer[i] != 0) {
                        bln = true;
                    }
                }
                if (bln) {
                    transformer.ft(toTransform);
                    doStuff(toTransform);
                } else {
                    try {
                        audioRecord = new AudioRecord(
                                MediaRecorder.AudioSource.DEFAULT, frequency,
                                channelConfiguration, audioEncoding, bufferSize);
                        audioRecord.startRecording();
                    } catch (IllegalStateException e) {
                        e.printStackTrace();
                        Log.e("Recording failed", e.toString());
                    }
                }
                if (isCancelled())
                    break;
            }
            try {
                audioRecord.stop();
            } catch (IllegalStateException e) {
                e.printStackTrace();
                Log.e("Stop failed", e.toString());
            }

It works fine for microphone. But I want to do this transformation on sound file(in raw folder). I tried using InputStreamReader to read the sound file content, but how to use this file data to apply transformation on file? I tried using a buffer using following code:

InputStream ins;
    ByteArrayOutputStream outputStream;
    int size = 0;
    byte[] buffer = new byte[1024];
 ins = getResources().openRawResource(R.raw.fire);
    outputStream = new ByteArrayOutputStream();
    transformer = new RealDoubleFFT(blockSize);
while ((size = ins.read(buffer, 0, 1024)) >= 0) {
                    outputStream.write(buffer, 0, size);
                    if (isCancelled())
                        break;
                    boolean bln = false;
                    for (int i = 0; i < buffer.length; i++) {
                        toTransform[i] = (double) buffer[i] / 32768.0;
                        if (buffer[i] != 0) {
                            bln = true;
                        }
                    }
                    if (bln) {
                        transformer.ft(toTransform);
                        doStuff(toTransform);
                    }
                }
                ins.close();

But it is not returning the correct data. Maybe the data received from file is not what the library wants. Any ideas how to apply FFT on sound file?

Whats the format of the sound files?Sound files usually contain additional information other than the sound signal like a header for example.This would mess up your fft. — cgew85, Dec 03 '14 at 15:04
you can't use an inputStreamReader, because the file is not raw sound binary. you need to decode the sound before FFTing it. — njzk2, Dec 03 '14 at 15:07
possible duplicate of [Calculate FFT from audio file](http://stackoverflow.com/questions/17565269/calculate-fft-from-audio-file) (the idea is that you have to decode the wav file first) — njzk2, Dec 03 '14 at 15:10
Are you sure you want to use an FFT do to do DTMF decoding ? It's probably not the simplest or most efficient method. Eight Goertzel filters is probably a better idea. — Paul R, Dec 03 '14 at 15:38

score 0 · Answer 1 · answered Dec 04 '14 at 04:10

0

You appear to be converting single bytes, but the format of a .wav/RIFF file, after the header (often 44 bytes), is usually 16-bit or 2-byte little-endian samples.

answered Dec 04 '14 at 04:10

hotpaw2

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What approach should I follow? – berserk Dec 04 '14 at 09:15

Performing dtmf-decoder FFT on sound file android

1 Answers1