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：

#import <UIKit/UIKit.h>
#import <AVFoundation/AVFoundation.h>
#import <CoreAudio/CoreAudioTypes.h>

@interface MicBlowViewController : UIViewController {
    AVAudioRecorder *recorder;
    NSTimer *levelTimer;
    double lowPassResults;
}
- (void)start;
- (void)levelTimerCallback:(NSTimer *)timer;

@end

#import "MicBlowViewController.h"
#import "MicManager.h"

@implementation MicBlowViewController

- (void)start {
    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 *setCategoryError = nil;
    
    [[AVAudioSession sharedInstance] setCategory: AVAudioSessionCategoryRecord error: &setCategoryError];
    
    NSError *error;
    
    recorder = [[AVAudioRecorder alloc] initWithURL:url settings:settings error:&error];
    if (recorder) {
        [recorder prepareToRecord];
        recorder.meteringEnabled = YES;
        [recorder record];
        levelTimer = [NSTimer scheduledTimerWithTimeInterval: 0.03 target: self selector: @selector(levelTimerCallback:) userInfo: nil repeats: YES];
    }
}


- (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;
    
    if (lowPassResults < 0.25)
    {
        NSLog(@"
 当前音量：%f 
",lowPassResults);
    }
    else
    {
        NSLog(@"
 有声音啦:    %f 
",lowPassResults);
        [levelTimer invalidate];
        [recorder release];
    }
}

@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。