how to set playback speed for android generated tones

I am using the AudioTrack class and have generated my own tones开发者_高级运维 in my Android application. However, I want to be able to control the speed of playback, and I can't figure out how.

I see the setLoopPoints method but that doesn't seem to do what I want (if anyone has used it and can explain that method to me that would be great, the api documentation doesn't help me much).

What I want to do:

As a point (here, a touch on the screen) gets closer to a target on the screen, I want to increase speed of the tones I'm generating. For example, farther away I would, say, have the tone playing 1 time in 1 second, but very close to the target, 5 times in 1 second. I am struggling to find out the best way to do this with Android sounds (generated tones or even .wav files saved to my res/raw).

Any help would be much appreciated!

Shani

You want to use the setPlaybackRate method for this:

http://developer.android.com/reference/android/media/AudioTrack.html

in conjunction with setLoopPoints. However, I believe there is probably a limit to how much you can speed up the file's "natural" playback rate, and the limit is probably 48 kHz (I'm not sure, though, and it may be device-dependent).

So, if you have a file that was recorded at, say, 8000 Hz, to get the effect you want you would set the loop count to 4 (so that it plays 5 times in a row) and set the playback rate to 40,000 (5 * 8000).

Since there is (probably) an upper limit to playback rate, your best approach might be to instead record the original sound at a high frequency, and slow down the playback as necessary to achieve the effect you want.

Update: setLoopPoints lets you specify two arbitrary locations within the file, such that when playback reaches the end looppoint the audio engine will wrap back around to the start looppoint. To loop the entire file, you would set the start looppoint to 0 and the end looppoint to the last frame in the file (the size of each frame is dependent upon the file's format - so a stereo file using 2 bytes per sample would have a frame size of 4, so the last frame is just the size of the audio data in bytes divided by 4).

To get 5 consecutive plays of your file, you would set the loop count to 4 (loopcount of 0 means the file plays once; -1 means it will loop forever).

Update 2: just read the docs some more - the upper limit for setPlaybackRate is documented as twice the rate returned by getNativeOutputSampleRate, which for most devices is probably 44,100 or 48,000 Hz. This means that a standard CD-quality WAV file can only be played back at twice its normal speed. A 22,050 Hz file could be played back at up to 4 times its normal speed, etc.