<edit: added the stop method following Jesse's comment.>

<edit: you'll need to include the following line in your AndroidManifest:

  <uses-permission android:name="android.permission.RECORD_AUDIO"></uses-permission>

otherwise, you'll get the following error: "Error creating AudioRecord instance: initialization check failed.">

1. import android.media.AudioRecord;
2. import android.media.AudioFormat;
3. import android.media.MediaRecorder;
4. 
   
5. final int RECORDER_SAMPLERATE = 44100;
6. final int RECORDER_CHANNELS = AudioFormat.CHANNEL_IN_MONO;
7. final int RECORDER_AUDIO_ENCODING = AudioFormat.ENCODING_PCM_16BIT;
8. 
   
9. short[] buffer = null;
10. AudioRecord audioRecord = null;
11. int bufferSize;
12. float volume = 0;
13. 
    
14. void setup() {
15.   bufferSize = AudioRecord.getMinBufferSize(RECORDER_SAMPLERATE,RECORDER_CHANNELS,RECORDER_AUDIO_ENCODING);
16.   audioRecord = new AudioRecord(MediaRecorder.AudioSource.MIC,
17.                                           RECORDER_SAMPLERATE, RECORDER_CHANNELS,RECORDER_AUDIO_ENCODING, bufferSize);
18.   audioRecord.startRecording();
19.   buffer = new short[bufferSize];
20. }
21. 
    
22. void draw() {
23.    background(200);
24.    int bufferReadResult = audioRecord.read(buffer, 0, bufferSize);
25.    volume = 0;
26.    for (int i = 0; i < bufferReadResult; i++) {
27.       volume = Math.max(Math.abs(buffer[i]), volume);
28.    }
29.    text("" + volume, 100, 100);   
30. }
31. 
    
32. void stop() {
33.   audioRecord.stop();
34.   audioRecord.release();
35. }

I've never tried to just get the buffer... hmmm.

Slightly different implementation below, but this is the start/stop methods I use...

In the console i get 'no library found for android.media'

It compiles and builds to my phone but then i get a fatal exception and it quits. 

startrecording() called an uninitialised AudioRecord

FFT Implementation

Works great, just remember buffersize MUST be a power of 2. Also PCM_16BIT encoding is best. Also the bigger the buffersize the more time it takes to capture each burst. If you need more accuracy I would go with decreasing sample rate over increasing buffersize. Just keep in mind nyquist limits it to being able to analyze to half the sample rate and lower.

This library wants to see floats not integers like the ones provided by the buffer. So I just cycled through and mapped it correctly [for 16bit of course.]

1. map(buffer[i], -32768, 32767, -1,1);

I had a lot of problems getting my app to launch properly without complaining about stop calls.

Then I tried this.

Also the permissions are set in the PDE under Android>Sketch Permissions, only one you need for basic audio stuff like setting up a buffer and doing an FFT analysis are RECORD_AUDIO