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implementing iphone Voice Memo: read many topics but i miss something

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];

} else

    NSLog([error description]);

       

[recorder updateMeters];

 

const double ALPHA = 0.05;

double peakPowerForChannel = pow(10, (0.05 * [recorder peakPowerForChannel:0]));//to have a decimal value

lowPassResults = ALPHA * peakPowerForChannel + (1.0 - ALPHA) * lowPassResults;  

 

NSLog(@"Average input: %f Peak input: %f Low pass results: %f", [recorder averagePowerForChannel:0], [recorder peakPowerForChannel:0], lowPassResults)

       

RMS_signal (V) = sqrt(sum(x^2) / N)

       

[recorder peakPowerForChannel:0]?

       

[NSNumber numberWithFloat: 44100.0],                 AVSampleRateKey,

       

Magnitude (dB) = 20.0 * log10(RMS_signal) + K