Play a beep that loop and change the frequency/speed

I am creating an iphone application that use audio. I want to play a beep sound that loop indefinitely.

I found an easy way to do that using the upper layer AVAudioPlayer and the numberOfLoops set to "-1". It works fine.

But now I want to play this audio and be able to change the rate / speed. It may works like the sound played by a car when approaching an obstacle. At the beginning the beep has a low frequency and this frequency accelerate till reaching a开发者_高级运维 continuous sound biiiiiiiiiiiip ... It seems this is not feasible using the high layer AVAudioPlayer, but even looking at AudioToolBox I found no solution.

Any help?

Take a look at Dave Dribin's A440 sample application, which plays a constant 440 Hz tone on the iPhone / iPad. It uses the lower-level Audio Queue Services, but it does what you're asking (short of the realtime tone adjustment, which would just require a tweak of the existing code).