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/*
* Copyright (C) 2004-2010 NXP Software
* Copyright (C) 2010 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/**********************************************************************************
$Author: beq07716 $
$Revision: 1000 $
$Date: 2010-06-28 13:08:20 +0200 (Mon, 28 Jun 2010) $
***********************************************************************************/
/****************************************************************************************/
/* */
/* Includes */
/* */
/****************************************************************************************/
#include "CompLim_private.h"
/****************************************************************************************/
/* */
/* FUNCTION: NonLinComp_D16 */
/* */
/* DESCRIPTION: */
/* Non-linear compression by companding. The function works on a sample by sample */
/* basis by increasing the level near the zero crossing. This gives a ttrade-off */
/* between THD and compression. It uses the equation: */
/* */
/* Output = Input + K * (Input - Input^2) if Input > 0 */
/* = Input + K * (Input + Input^2) if Input <= 0 */
/* */
/* The value of K controls the amount of compression and as a side effect the amount */
/* distortion introduced. The amount of compression is signal dependent and the values */
/* given below are approximate. */
/* */
/* Gain (fractional) Gain (integer) Compression Pk-Pk THD */
/* 1.0 32767 +6dB 16dB */
/* 0.78 25559 +5dB 19dB */
/* 0.6 19661 +4dB 21dB */
/* 0.41 13435 +3dB 24dB */
/* 0.26 8520 +2dB 28dB */
/* 0.12 3932 +1dB 34dB */
/* 0.0 0 +0dB 98dB */
/* */
/* PARAMETERS: */
/* Gain - compression control parameter */
/* pDataIn - pointer to the input data buffer */
/* pDataOut - pointer to the output data buffer */
/* BlockLength - number of samples to process */
/* */
/* RETURNS: */
/* None */
/* */
/* NOTES: */
/* */
/****************************************************************************************/
void NonLinComp_D16(LVM_INT16 Gain,
LVM_INT16 *pDataIn,
LVM_INT16 *pDataOut,
LVM_INT32 BlockLength)
{
LVM_INT16 Sample; /* Input samples */
LVM_INT32 SampleNo; /* Sample index */
LVM_INT16 Temp;
/*
* Process a block of samples
*/
for(SampleNo = 0; SampleNo<BlockLength; SampleNo++)
{
/*
* Read the input
*/
Sample = *pDataIn;
pDataIn++;
/*
* Apply the compander, this compresses the signal at the expense of
* harmonic distortion. The amount of compression is control by the
* gain factor
*/
if ((LVM_INT32)Sample != -32768)
{
Temp = (LVM_INT16)((Sample * Sample) >> 15);
if(Sample >0)
{
Sample = (LVM_INT16)(Sample + ((Gain * (Sample - Temp)) >> 15));
}
else
{
Sample = (LVM_INT16)(Sample + ((Gain * (Sample + Temp)) >> 15));
}
}
/*
* Save the output
*/
*pDataOut = Sample;
pDataOut++;
}
}
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