iOS之声音捕捉

现在需要在ios上实现这样一个功能：

监听外部的声音，当有声音且达到一定的分贝后，通知相关事件就可以了。

真机测试已经通过的代码：

主要的是一个类：

 1 #import <UIKit/UIKit.h>
 2 #import <AVFoundation/AVFoundation.h>
 3 #import <CoreAudio/CoreAudioTypes.h>
 4 
 5 @interface MicBlowViewController : UIViewController {
 6     AVAudioRecorder *recorder;
 7     NSTimer *levelTimer;
 8     double lowPassResults;
 9 }
10 - (void)start;
11 - (void)levelTimerCallback:(NSTimer *)timer;
12 
13 @end

 1 #import "MicBlowViewController.h"
 2 #import "MicManager.h"
 3 
 4 @implementation MicBlowViewController
 5 
 6 - (void)start {
 7     NSURL *url = [NSURL fileURLWithPath:@"/dev/null"];
 8     
 9     NSDictionary *settings = [NSDictionary dictionaryWithObjectsAndKeys:
10                               [NSNumber numberWithFloat: 44100.0],                 AVSampleRateKey,
11                               [NSNumber numberWithInt: kAudioFormatAppleLossless], AVFormatIDKey,
12                               [NSNumber numberWithInt: 1],                         AVNumberOfChannelsKey,
13                               [NSNumber numberWithInt: AVAudioQualityMax],         AVEncoderAudioQualityKey,
14                               nil];
15     
16     NSError *setCategoryError = nil;
17     
18     [[AVAudioSession sharedInstance] setCategory: AVAudioSessionCategoryRecord error: &setCategoryError];
19     
20     NSError *error;
21     
22     recorder = [[AVAudioRecorder alloc] initWithURL:url settings:settings error:&error];
23     if (recorder) {
24         [recorder prepareToRecord];
25         recorder.meteringEnabled = YES;
26         [recorder record];
27         levelTimer = [NSTimer scheduledTimerWithTimeInterval: 0.03 target: self selector: @selector(levelTimerCallback:) userInfo: nil repeats: YES];
28     }
29 }
30 
31 
32 - (void)levelTimerCallback:(NSTimer *)timer {
33     [recorder updateMeters];
34     
35     const double ALPHA = 0.05;
36     double peakPowerForChannel = pow(10, (0.05 * [recorder peakPowerForChannel:0]));
37     lowPassResults = ALPHA * peakPowerForChannel + (1.0 - ALPHA) * lowPassResults;
38     
39     if (lowPassResults < 0.25)
40     {
41         NSLog(@"
 当前音量：%f 
",lowPassResults);
42     }
43     else
44     {
45         NSLog(@"
 有声音啦:    %f 
",lowPassResults);
46         [levelTimer invalidate];
47         [recorder release];
48     }
49 }
50 
51 @end

代码有借鉴网络，加上自己的后期加工，成为了自己的项目。需要注意的是加上：

18行的代码。

否则会出现声音峰值的返回永远是－160。

然后就是开一个timer循环监听外部声音的情况，达到一定峰值，触发相关函数进行处理。