Question

I’m trying to fill a buffer with microphone input and analyze the contents. I create my buffers with:

    int bufferSize=AudioRecord.getMinBufferSize(8000,AudioFormat.CHANNEL_IN_MONO,
            AudioFormat.ENCODING_PCM_16BIT);
    short[] buffer1 = new short[bufferSize];

Then in a separate class called Recorder, I have the following relevant code:

public short[] fillBuffer(short[] audioData, int bufferSize) {

    AudioRecord recorder = new AudioRecord(AudioSource.MIC, 8000, AudioFormat.CHANNEL_IN_MONO,
            AudioFormat.ENCODING_PCM_16BIT, bufferSize); // instantiate the
                                                            // AudioRecorder

    if (recorder.getRecordingState() == android.media.AudioRecord.RECORDSTATE_STOPPED)
        recorder.startRecording(); // check to see if the Recorder
                                    // has stopped or is not
                                    // recording, and make it
                                    // record.

    recorder.read(audioData, 0, bufferSize); // read the PCM
                                                // audio data
                                                // into the
                                                // audioData
                                                // array

    if (recorder.getState() == android.media.AudioRecord.RECORDSTATE_RECORDING)
        recorder.stop(); // stop the recorder

    return audioData;

}

Then, when I call:

recorder.fillBuffer(buffer1, bufferSize);

and log the output, it always shows that the buffer is half full of what seems to be valid audio data, but half full of zeros.

Creating a buffer of half the normal size just threw an error, so I know it’s actually storing zeros. It isn’t just some weirdness with the buffer size. Am I doing something obviously wrong here? Keep in mind that this is my first Android application, though I’m pretty familiar with Java.

Answer 1

I actually think I may have solved this. I wrote this previously in C++ using Windows WaveIn and I used a short int array for the buffer, so I naturally tried to do that here. After reading the documentation again, though, it looks like I need a byte[] array. After changing it, it seems to work. Thanks for your help though, everyone!