检测iPhone麦克风上的吹气？

我试图检测用户何时对着iPhone的麦克风吹气。现在我正在使用SCListener类从调用

在一段时间内。然而，有时候当我不吹的时候，这种情况就会出现。有没有人有任何示例代码来检查用户是否正在向麦克风吹气？

我建议首先使用电源信号。总有一些瞬态噪声会干扰瞬时读数；低通滤波有助于缓解这种情况。一个简单的低通滤波器应该是这样的：

// Make this a global variable, or a member of your class:
double micPower = 0.0;
// Tweak this value to your liking (must be between 0 and 1)
const double ALPHA = 0.05;

// Do this every 'tick' of your application (e.g. every 1/30 of a second)
double instantaneousPower = [[SCListener sharedListener] peakPower];

// This is the key line in computing the low-pass filtered value
micPower = ALPHA * instantaneousPower + (1.0 - ALPHA) * micPower;

if(micPower > THRESHOLD)  // 0.99, in your example
    // User is blowing on the microphone

---

本教程适用于模拟器，但不适用于iphone。iphone麦克风没有响应。使用return，因为

低通结果

大于0.55。这很好：

-(void)readyToBlow1 { 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.meteringEnabled = YES;
        [recorder record];
        levelTimer = [NSTimer scheduledTimerWithTimeInterval: 0.01 target: self selector: @selector(levelTimerCallback1:) userInfo: nil repeats: YES];
    } else
        NSLog(@"%@",[error description]);
}

-(void)levelTimerCallback1:(NSTimer *)timer { [recorder updateMeters];
    const double ALPHA = 0.05; 
    double peakPowerForChannel = pow(10, (0.05 * [recorder peakPowerForChannel:0])); 
    double lowPassResults = ALPHA * peakPowerForChannel + (1.0 - ALPHA) * lowPassResults; 
    if (lowPassResults > 0.55) { 
        lowPassResults = 0.0;
        [self invalidateTimers];
        NextPhase *objNextView =[[NextPhase alloc]init];
        [UIView transitionFromView:self.view
                      toView:objNextView.view
                      duration:2.0
                      options:UIViewAnimationOptionTransitionCurlUp
                      completion:^(BOOL finished) {}
        ];
        [self.navigationController pushViewController:objNextView animated:NO];
    **return;**
    }
}

---

在iPhone上运行时，应在[recorder prepareToRecorder]之后添加以下代码

[[AVAudioSession sharedInstance] setCategory:AVAudioSessionCategoryPlayAndRecord error:nil];
[[AVAudioSession sharedInstance] setActive:YES error:nil];

---

试试这个，对我来说很好。谢谢@廖金华

- (void)viewDidLoad {
   [super viewDidLoad];

lowPassResults = 0.0;
[self readyToBlow1];

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];
    [[AVAudioSession sharedInstance] setCategory:AVAudioSessionCategoryPlayAndRecord error:nil];
    [[AVAudioSession sharedInstance] setActive:YES error:nil];
    recorder.meteringEnabled = YES;
    [recorder record];
    levelTimer = [NSTimer scheduledTimerWithTimeInterval: 0.03 target: self selector: @selector(levelTimerCallback:) userInfo: nil repeats: YES];
} else
    NSLog([error description]); 

}

- (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(@"lowpassResult is %f",lowPassResults);
if (lowPassResults > 0.95){
    NSLog(@"Mic blow detected");
    [levelTimer invalidate];
}
}

---

也许风在刮。：）对不起，这个问题让我笑了。哈，不。即使我在里面，只要轻敲屏幕就会触发该功能。如果音量超过阈值，你能停止录音吗？意思是如果有一个voip应用程序，并且不希望消防车警报器在对话中咆哮，我可以在超过阈值后暂停麦克风吗？现在你可以看到lowPassResults。只是没有对准。抱歉：）我收到lowPassResults的编译器错误，因为它正用于初始化它的方程。lowPassResults是否应该在其他地方初始化？是的，您必须在viewDidLoad中初始化lowPassResults，或者ViewWill将根据需要显示。只需初始化为lowPassResults=0.0；有人能解释一下这段代码中的“低通滤波器”吗。据我所知，低通滤波器会从测量值中排除高频声音。然而，这里没有提到声音频率。PeakPower ForChannel以分贝为单位返回音量。而代码只是操纵那个值。我遗漏了什么？我已经找了3个小时了。现在可以用了！。

- (void)viewDidLoad {
   [super viewDidLoad];

lowPassResults = 0.0;
[self readyToBlow1];

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];
    [[AVAudioSession sharedInstance] setCategory:AVAudioSessionCategoryPlayAndRecord error:nil];
    [[AVAudioSession sharedInstance] setActive:YES error:nil];
    recorder.meteringEnabled = YES;
    [recorder record];
    levelTimer = [NSTimer scheduledTimerWithTimeInterval: 0.03 target: self selector: @selector(levelTimerCallback:) userInfo: nil repeats: YES];
} else
    NSLog([error description]); 

}

- (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(@"lowpassResult is %f",lowPassResults);
if (lowPassResults > 0.95){
    NSLog(@"Mic blow detected");
    [levelTimer invalidate];
}
}