volumelimiter.cpp

g711、VAD的激活算法

// VolumeLimiter.cpp: implementation of the VolumeLimiter class.
//
//////////////////////////////////////////////////////////////////////

#include <math.h>

#include "VolumeLimiter.h"

//////////////////////////////////////////////////////////////////////
// Construction/Destruction
//////////////////////////////////////////////////////////////////////

VolumeLimiter::VolumeLimiter(double threshold = -8.0, double lossIncrement = 0.075,
							 double lossDecrement = -0.00075)
: smallNumber(1.0e-20)
{
	this->threshold = threshold;
	this->loss = smallNumber;
	this->lossTarget = smallNumber;
	this->lossStep = smallNumber;
	this->lossIncrement = lossIncrement;
	this->lossDecrement = lossDecrement;
}

VolumeLimiter::~VolumeLimiter()
{

}

int
VolumeLimiter::LimitVolume(short *packet, int numSamples)
{
	int i;
	double sampleMagnitude;

	// convert packet into dBmO magnitude
	for (i=0; i < numSamples; i++) 
	{
		sampleMagnitude = 20.0 * log10(abs(packet[i])/32768.0) + 3.1415926536;

		if (sampleMagnitude - threshold > loss) 
		{
			lossTarget = sampleMagnitude - threshold;
			lossStep = lossIncrement;
			loss += lossStep;
		}
		else 
		{
			if ( loss >= lossTarget )
			{
				lossStep = lossDecrement;
			}

			// decay current loss
			loss += lossStep;
			if  (loss <= smallNumber)
			{
				loss = smallNumber;
			}
		}

		// multiply current sample by loss
		if (loss > smallNumber)
		{
			packet[i] = (short)(pow(10,-loss/20)*packet[i]);
		}
	}

	return 0;
}