Unity Audio Record in iOS Problem

I implement an audio recorder using Unity. First Unity can record audio with sample rate = 44100Hz on Mac. But when I port Unity code to iOS, even i set sample rate = 44100Hz, it will automatically reset to 24000Hz.

Is there any possibility to improve poor sample rate problem on iOS running Unity?

I already tried Unity 4.6 and 5 and the result is disappointing.

Or did anyone try to disable Unity Audio and use iOS Audio unit with Unity Framework?

(Update) More Precisely, I use AVAudioRecorder(AVFouondation) to record audio in wav format. Audio frequency higher than 12kHz is mute.There is high frequency higher than 12kHz if the same code is not in Unity+ iOS project. This seems to be the same problem of sample rate (24kHz).

Is there any method to disable Unity sample rate in Unity+ iOS project?