iOS音频频谱动画，仿QQ录音频谱

先上效果图：

有需要的请移步GitHub下载：
https://github.com/HuangGY1993/GYSpectrum

用法很简单，示例：

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];

使用前请注意：

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)];