Can we Increase the gain of mic of an android phone?

Question

I am trying to increase the gain of the mic of an android phone so that it will be capable of hearing very minute sounds.Is it possible? Can you please help me with this.

Answer 1

this link should bring you further. use setStreamVolume(...) to set volume higher. but note that there is a maximum that can be asked for by calling getStreamMaxVolume(...). so mic gain is probably limited by hardware i would guess. so it is rather not possible to do this "on-fly" but what about recording a bit, trying to amplify a special frequency by equalizer and then recognize something like a heartbeat? sounds hard but maybe possible.

Answer 2

Audio gain control

public class MainActivity extends Activity {

public static final int SAMPLE_RATE = 16000;

private AudioRecord mRecorder;
private File mRecording;
private short[] mBuffer;
private final String startRecordingLabel = "Start recording";
private final String stopRecordingLabel = "Stop recording";
private boolean mIsRecording = false;
private ProgressBar mProgressBar;
float iGain = 1.0f;
CheckBox gain;

protected int bitsPerSamples = 16;

@Override
public void onCreate(final Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.fragment_main);

    initRecorder();

    Button bluetooth = (Button)findViewById(R.id.blue);
    gain = (CheckBox) findViewById(R.id.checkBox1);
    mProgressBar = (ProgressBar) findViewById(R.id.progressBar);

    final Button button = (Button) findViewById(R.id.start);
    button.setText(startRecordingLabel);

    bluetooth.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub
            Intent i = new Intent("");
        }
    });
    gain.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {

        @Override
        public void onCheckedChanged(CompoundButton buttonView,
                boolean isChecked) {

            if (gain.isChecked()) {
                iGain = 5.0f;

            } else {
                iGain = 2.0f;
            }
        }
    });

    button.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(final View v) {
            if (!mIsRecording) {
                button.setText(stopRecordingLabel);
                mIsRecording = true;
                mRecorder.startRecording();
                mRecording = getFile("raw");
                startBufferedWrite(mRecording);
            } else {
                button.setText(startRecordingLabel);
                mIsRecording = false;
                mRecorder.stop();
                File waveFile = getFile("wav");
                try {
                    rawToWave(mRecording, waveFile);
                } catch (IOException e) {
                    Toast.makeText(MainActivity.this, e.getMessage(),
                            Toast.LENGTH_SHORT).show();
                }
                Toast.makeText(MainActivity.this,
                        "Recorded to " + waveFile.getName(),
                        Toast.LENGTH_SHORT).show();
            }
        }
    });
}

@Override
public void onDestroy() {
    mRecorder.release();
    super.onDestroy();
}

private void initRecorder() {
    int bufferSize = AudioRecord.getMinBufferSize(SAMPLE_RATE,
            AudioFormat.CHANNEL_IN_MONO, AudioFormat.ENCODING_PCM_16BIT);
    mBuffer = new short[bufferSize];
    mRecorder = new AudioRecord(MediaRecorder.AudioSource.MIC, SAMPLE_RATE,
            AudioFormat.CHANNEL_IN_MONO, AudioFormat.ENCODING_PCM_16BIT,
            bufferSize);
}

private void startBufferedWrite(final File file) {
    new Thread(new Runnable() {
        @Override
        public void run() {
            DataOutputStream output = null;
            try {
                output = new DataOutputStream(new BufferedOutputStream(
                        new FileOutputStream(file)));
                while (mIsRecording) {
                    double sum = 0;

                    int readSize = mRecorder.read(mBuffer, 0,
                            mBuffer.length);

                    final int bytesPerSample = bitsPerSamples / 8;
                    final int emptySpace = 64 - bitsPerSamples;
                    int byteIndex = 0;
                    int byteIndex2 = 0;
                    int temp = 0;
                    int mLeftTemp = 0;
                    int mRightTemp = 0;
                    int a = 0;
                    int x = 0;

                    for (int frameIndex = 0; frameIndex < readSize; frameIndex++) {

                        for (int c = 0; c < 1; c++) {

                            if (iGain != 1) {

                                long accumulator = 0;
                                for (int b = 0; b < bytesPerSample; b++) {

                                    accumulator += ((long) (mBuffer[byteIndex++] & 0xFF)) << (b * 8 + emptySpace);
                                }

                                double sample = ((double) accumulator / (double) Long.MAX_VALUE);
                                sample *= iGain;
                                int intValue = (int) ((double) sample * (double) Integer.MAX_VALUE);

                                for (int i = 0; i < bytesPerSample; i++) {
                                    mBuffer[i + byteIndex2] = (byte) (intValue >>> ((i + 2) * 8) & 0xff);
                                }
                                byteIndex2 += bytesPerSample;

                            }
                        }// end for(channel)

                        // mBuffer[frameIndex] *=iGain;
                        if (mBuffer[frameIndex] > 32765) {
                            mBuffer[frameIndex] = 32767;

                        } else if (mBuffer[frameIndex] < -32767) {
                            mBuffer[frameIndex] = -32767;
                        }
                        output.writeShort(mBuffer[frameIndex]);
                        sum += mBuffer[frameIndex] * mBuffer[frameIndex];

                    }

                    if (readSize > 0) {
                        final double amplitude = sum / readSize;
                        mProgressBar.setProgress((int) Math.sqrt(amplitude));
                    }
                }
            } catch (IOException e) {
                Toast.makeText(MainActivity.this, e.getMessage(),
                        Toast.LENGTH_SHORT).show();
            } finally {
                mProgressBar.setProgress(0);
                if (output != null) {
                    try {
                        output.flush();
                    } catch (IOException e) {
                        Toast.makeText(MainActivity.this, e.getMessage(),
                                Toast.LENGTH_SHORT).show();
                    } finally {
                        try {
                            output.close();
                        } catch (IOException e) {
                            Toast.makeText(MainActivity.this, e.getMessage(),
                                    Toast.LENGTH_SHORT).show();
                        }
                    }
                }
            }
        }
    }).start();
}

private void rawToWave(final File rawFile, final File waveFile)
        throws IOException {

    byte[] rawData = new byte[(int) rawFile.length()];
    DataInputStream input = null;
    try {

        input = new DataInputStream(new FileInputStream(rawFile));
        input.read(rawData);
    } finally {
        if (input != null) {
            input.close();
        }
    }

    DataOutputStream output = null;
    try {
        output = new DataOutputStream(new FileOutputStream(waveFile));
        // WAVE header
        // see http://ccrma.stanford.edu/courses/422/projects/WaveFormat/
        writeString(output, "RIFF"); // chunk id
        writeInt(output, 36 + rawData.length); // chunk size
        writeString(output, "WAVE"); // format
        writeString(output, "fmt "); // subchunk 1 id
        writeInt(output, 16); // subchunk 1 size
        writeShort(output, (short) 1); // audio format (1 = PCM)
        writeShort(output, (short) 1); // number of channels
        writeInt(output, SAMPLE_RATE); // sample rate
        writeInt(output, SAMPLE_RATE * 2); // byte rate
        writeShort(output, (short) 2); // block align
        writeShort(output, (short) 16); // bits per sample
        writeString(output, "data"); // subchunk 2 id
        writeInt(output, rawData.length); // subchunk 2 size
        // Audio data (conversion big endian -> little endian)
        short[] shorts = new short[rawData.length / 2];
        ByteBuffer.wrap(rawData).order(ByteOrder.LITTLE_ENDIAN)
                .asShortBuffer().get(shorts);
        ByteBuffer bytes = ByteBuffer.allocate(shorts.length * 2);

        for (short s : shorts) {

            // Apply Gain
            /*
             * s *= iGain; if(s>32767) { s=32767; } else if(s<-32768) {
             * s=-32768; }
             */
            bytes.putShort(s);
        }
        output.write(bytes.array());
    } finally {
        if (output != null) {
            output.close();
        }
    }
}

private File getFile(final String suffix) {
    Time time = new Time();
    time.setToNow();
    return new File(Environment.getExternalStorageDirectory(),
            time.format("%Y%m%d%H%M%S") + "." + suffix);
}





private void writeInt(final DataOutputStream output, final int value)
        throws IOException {
    output.write(value >> 0);
    output.write(value >> 8);
    output.write(value >> 16);
    output.write(value >> 24);
}

private void writeShort(final DataOutputStream output, final short value)
        throws IOException {
    output.write(value >> 0);
    output.write(value >> 8);
}

private void writeString(final DataOutputStream output, final String value)
        throws IOException {
    for (int i = 0; i < value.length(); i++) {
        output.write(value.charAt(i));
    }
}
}