IOS 8: Real Time Sound Processing and Sound Pitching - OpenAL or other framework

I'm trying to realize an app which plays a sequence of tones in a loop. Actually, I use OpenAL and my experiences with such framework are positive, as I can perform a sound pitch also.

Here's the scenario:

1. load a short sound (3 seconds) from a CAF file


2. play that sound in a loop and perform a sound shift also.

This works well, provided that the tact rate isn't too high - I mean a time of more than 10 milliseconds per tone.

Anyhow, my NSTimer (which embeds my sound sequence to play) should be configurable - and as soon as my tact rate increases (I mean less than 10 ms per tone), the sound is no more echoed correctly - even some tones are dropped in an obvious random way.

It seems that real time sound processing becomes an issue. I'm still a novice in IOS programming, but I believe that Apple sets a limit concerning time consumption and/or semaphore.

Now my questions:

1. OpenAL is written in C - until now, I didn't understand the whole code and philosophy behind that framework. Is there a possibility to resolve my above mentioned problem making some modifications - I mean setting flags/values or overwriting certain methods?


2. If not, do you know another IOS sound framework more appropriate for such kind of real time sound processing?

Many thanks in advance! I know that it deals with a quite extraordinary and difficult problem - maybe s.o. of you has resolved a similar one? Just to emphasize: sound pitch must be guaranteed!