Android AudioRecord questions?

Question

I have been messing around with the AudioRecord feature of the Android API and found some strange behaviors with it.

Background info: My phone is a HTC Incredible I

Answer 1

I might be able to help a tiny bit. However, I am in the same situation as you so I can only tell you about my experiences.

I believe you can get your device's preferred sampleRate like so:

int sampleRate = AudioTrack.getNativeOutputSampleRate(AudioManager.STREAM_SYSTEM);

The 16Bit encoding mode is the only one that works with AudioRecord. I am unsure why you are getting 8Bit like output (right?). Maybe someone knows.

I am also unsure how you pull the amplitude from the retrieved bytes, did you do this?

Finally, I believe you need to use the periodic listener functions, like so:

int sampleRate = AudioTrack.getNativeOutputSampleRate(AudioManager.STREAM_SYSTEM);
int channelMode = AudioFormat.CHANNEL_IN_MONO;
int encodingMode = AudioFormat.ENCODING_PCM_16BIT;
int bufferSize = AudioRecord.getMinBufferSize(sampleRate, channelMode, encodingMode);

AudioRecord recorder = new AudioRecord(MediaRecorder.AudioSource.MIC, sampleRate, channelMode, encodingMode, bufferSize);

recorder.setPositionNotificationPeriod(intervalFrames);
recorder.setRecordPositionUpdateListener(recordListener);
recorder.startRecording();

private RecordListener recordListener = new RecordListener();
private class RecordListener implements AudioRecord.OnRecordPositionUpdateListener {
    public void onMarkerReached(AudioRecord recorder) {
        Log.v("MicInfoService", "onMarkedReached CALL");
    }

    public void onPeriodicNotification(AudioRecord recorder) {
        Log.v("MicInfoService", "onPeriodicNotification CALL");
    }
}

There are two big questions here which I cannot answer and want to know the answer of myself as well:

1. What should be set as intervalFrames?
2. Why are the listener methods never called?

I wish I could help more.