iphone-peakPowerForChannel function in AVAudioRecorder doesn't work

问题

I am trying to use an AVAudioRecorder instance to record sound, the whole recording progress runs well, except that when I call [recorder peakPowerForChannel:0] trying to get the volume, the return value is always 0, that's pretty odd..

I have checked the recorded audio file, it's totally fine. Then I use AVAudioPlayer to play it, and during playing, i call [player peakPowerForChannel:0], the return value seems to be right and make sense.

How can I get the right value ? I have set that: recoder.meteringEnabled = YES, and called [recorder updateMeters] every time I call [recorder peakPowerForChannel:0]. The initial of recorder is as follows:

NSMutableDictionary *recordSetting = [[NSMutableDictionary alloc] init];
//General Audio Format Settings 
[recordSetting setValue:[NSNumber numberWithInt: 'ima4'] forKey:AVFormatIDKey]; 
[recordSetting setValue:[NSNumber numberWithFloat:44100.0] forKey:AVSampleRateKey]; 
[recordSetting setValue:[NSNumber numberWithInt: 2] forKey:AVNumberOfChannelsKey];
//Linear PCM Format Settings 
[recordSetting setValue:[NSNumber numberWithInt: 32] forKey:AVLinearPCMBitDepthKey]; 
[recordSetting setValue:[NSNumber numberWithBool:NO] forKey:AVLinearPCMIsBigEndianKey]; 
[recordSetting setValue:[NSNumber numberWithBool:NO] forKey:AVLinearPCMIsFloatKey];
//Encoder Settings 
[recordSetting setValue:[NSNumber numberWithInt:AVAudioQualityMedium] forKey:AVEncoderAudioQualityKey]; 
[recordSetting setValue:[NSNumber numberWithInt:96] forKey:AVEncoderBitRateKey]; 
[recordSetting setValue:[NSNumber numberWithInt:16] forKey:AVEncoderBitDepthHintKey];
//Sample Rate Conversion Settings 
[recordSetting setValue:[NSNumber numberWithInt:AVAudioQualityHigh] forKey:AVSampleRateConverterAudioQualityKey];
recorder = [[AVAudioRecorder alloc] initWithURL:url settings:recordSetting error:nil];
recorder.meteringEnabled = YES;

回答1:

Try this. It works for me. I think the problem you are experiencing is that you don't call updateMeters

Set up the recorder once (this part of your code is fine)

[recorder prepareToRecord];
recorder.meteringEnabled = YES;
//Start the actual Recording
[recorder record];

NSTimer *TimerUpdate = [NSTimer scheduledTimerWithTimeInterval:.1 
   target:self selector:@selector(timerTask) userInfo:nil repeats:YES];

Then define this small routine to get the peak level:

- (void) timerTask {
   [recorder updateMeters];
   float level = [recorder peakPowerForChannel:0];
   NSLog(@"%f", level);
}

回答2:

You have to wait to set the meteringEnabled property until either you've either sent the record message or the prepareToRecord message.

In your specific case, add:

[recorder prepareToRecord];

before

recorder.meteringEnabled = YES;

and it should work.

回答3:

try to test the peak of channels 1 or 2 and not 0

回答4:

It is supposed to return 0, indicating 0dB and maximum power. From Apple's documentation:

Return Value
The current peak power, in decibels, for the sound being recorded. A return value of 0 dB indicates full scale, or maximum power; a return value of -160 dB indicates minimum power (that is, near silence).

http://developer.apple.com/library/ios/#documentation/AVFoundation/Reference/AVAudioRecorder_ClassReference/Reference/Reference.html

You want averagePowerForChannel: instead.

来源：https://stackoverflow.com/questions/1191617/iphone-peakpowerforchannel-function-in-avaudiorecorder-doesnt-work

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avaudiorecorder