What I am trying to do is to take the float value from EZAudio and convert it into decibels.

EZAudioDelegate

这是我的简化EZAudio Delegate for getting Microphone Data：

- (void)microphone:(EZMicrophone *)microphone hasAudioReceived:(float **)buffer withBufferSize:(UInt32)bufferSize withNumberOfChannels:(UInt32)numberOfChannels {
    /*
     *  Returns a float array called buffer that contains the stereo signal data
     *  buffer[0] is the left audio channel
     *  buffer[1] is the right audio channel
     */

    // Using a separate audio thread to not block the main UI thread
    dispatch_async(dispatch_get_main_queue(),^{

        float decibels = [self getDecibelsFromVolume:buffer withBufferSize:bufferSize];

        NSLog(@"Decibels: %f",decibels);

    });

}

问题

The problem is that after implementing solutions from the links below,I do not understand how it works. If someone could explain how it converts volume to decibels I would be very grateful

> How to convert audio input to DB? #85
> How to change the buffer size to increase FFT window? #50
> Changing Buffer Size #84

代码

该解决方案使用Accelerate Framework中的以下方法将卷转换为分贝：

> vDSP_vsq
> vDSP_meanv
> vDSP_vdbcon

以下是EZAudio Delegate所调用的getDecibelsFromVolume方法.它从委托中传递了float ** buffer和bufferSize.

- (float)getDecibelsFromVolume:(float**)buffer withBufferSize:(UInt32)bufferSize {

    // Decibel Calculation.

    float one = 1.0;
    float meanVal = 0.0;
    float tiny = 0.1;
    float lastdbValue = 0.0;

    vDSP_vsq(buffer[0],1,buffer[0],bufferSize);

    vDSP_meanv(buffer[0],&meanVal,bufferSize);

    vDSP_vdbcon(&meanVal,&one,0);


    // Exponential moving average to dB level to only get continous sounds.

    float currentdb = 1.0 - (fabs(meanVal) / 100);

    if (lastdbValue == INFINITY || lastdbValue == -INFINITY || isnan(lastdbValue)) {
        lastdbValue = 0.0;
    }

    float dbValue = ((1.0 - tiny) * lastdbValue) + tiny * currentdb;

    lastdbValue = dbValue;

    return dbValue;
}