iPhone 麦克风电平：代码在一个项目中有效，在另一个项目中无效

Question

此 教程 代码适用于我。我将其设置为吐出 lowPAssResult 的值。在手机上运行它，果然，正如预期的那样...

2011-07-04 14:28:08.672 MicBlow[280:707] 检测到麦克风打击：0.036449 ...等等，如果我向它吹气，它的价值就会上升。一切都好。

但是当我把它放到我自己的项目框架中时，它不起作用。我将此代码放入我的 init 函数中...

//Set up the mic stuff
NSURL *url = [NSURL fileURLWithPath:@"/dev/null"];

NSDictionary *settings = [NSDictionary dictionaryWithObjectsAndKeys:
                          [NSNumber numberWithFloat: 44100.0],                 AVSampleRateKey,
                          [NSNumber numberWithInt: kAudioFormatAppleLossless], AVFormatIDKey,
                          [NSNumber numberWithInt: 1],                         AVNumberOfChannelsKey,
                          [NSNumber numberWithInt: AVAudioQualityMax],         AVEncoderAudioQualityKey,
                          nil];

NSError *error;

recorder = [[AVAudioRecorder alloc] initWithURL:url settings:settings error:&error];

if (recorder) 
{
    [recorder prepareToRecord];
    [recorder record];
    recorder.meteringEnabled = YES;        
    levelTimer = [NSTimer scheduledTimerWithTimeInterval: 0.03 target: self selector: @selector(levelTimerCallback:) userInfo: nil repeats: YES];
} 

并添加了此回调

- (void)levelTimerCallback:(NSTimer *)timer {
[recorder updateMeters];

const double ALPHA = 0.05;
double peakPowerForChannel = pow(10, (0.05 * [recorder peakPowerForChannel:0]));
lowPassResults = ALPHA * peakPowerForChannel + (1.0 - ALPHA) * lowPassResults;  

    NSLog(@"Mic blow detected -  peakPowerForChannel : %f, lowPassResults: %f",peakPowerForChannel,lowPassResults);
}

并且输出如下所示；

2011-07-04 14:30:32.974 MinuteGames[290:707] 检测到麦克风打击：0.000001 反复。每一帧

无论我吹了多少。请帮忙，我确信这一定很简单！