SpectrumView * spectrumView = [[SpectrumView alloc] initWithFrame:CGRectMake(CGRectGetMidX(self.view.frame) - 100,180,200, 40.0)];
    spectrumView.text = [NSString stringWithFormat:@"%d",0];
    __weak SpectrumView * weakWaver = spectrumView;
    spectrumView.itemLevelCallback = ^() {

    [self.audioRecorder updateMeters];

    //取得第一个通道的音频，音频强度范围是-160到0
    float power = [self.audioRecorder averagePowerForChannel:0];
    weakWaver.level = power;

    };
    [self.view addSubview:spectrumView];

    SpectrumView.frame.size.width / SpectrumView.numberOfItems >= 5

    默认SpectrumView.numberOfItems = 20 (可修改，必须为偶数)，所以SpectrumView.frame.size.width默认要大于100
    例如：SpectrumView * spectrumView = [[SpectrumView alloc] initWithFrame:CGRectMake(0,0,100,40)];