AVAudioSession *audioSession = [AVAudioSession sharedInstance];
 
NSError* error = nil;
if (audioSession.isInputAvailable) [audioSession setCategory:AVAudioSessionCategoryPlayAndRecord error:&error];
if(error){
    return;
}
 
[audioSession setActive:YES error:&error];
if(error){
    retur;
}
 
self.engine = [[[AVAudioEngine alloc] init] autorelease];
 
AVAudioMixerNode* mixer = [self.engine mainMixerNode];
AVAudioInputNode* input = [self.engine inputNode];
[self.engine connect:input to:mixer format:[input inputFormatForBus:0]];
 
// tap ... 1 call in 16537Frames
// It does not change even if you change the bufferSize
[input installTapOnBus:0 bufferSize:4096 format:[input inputFormatForBus:0] block:^(AVAudioPCMBuffer* buffer,AVAudioTime* when) {
 
    for (UInt32 i = 0; i < buffer.audioBufferList->mNumberBuffers; i++) {
        Float32 *data = buffer.audioBufferList->mBuffers[i].mData;
        UInt32 frames = buffer.audioBufferList->mBuffers[i].mDataByteSize / sizeof(Float32);
 
        // create waveform
        ...
    }
}];
 
[self.engine startAndReturnError:&error];
if (error) {
    return;
}