NonLinComp_D16.c revision 2c8e5cab3faa6d360e222b7a6c40a80083d021ac 
1/*
2 * Copyright (C) 2004-2010 NXP Software
3 * Copyright (C) 2010 The Android Open Source Project
4 *
5 * Licensed under the Apache License, Version 2.0 (the "License");
6 * you may not use this file except in compliance with the License.
7 * You may obtain a copy of the License at
8 *
9 *      http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17
18/**********************************************************************************
19
20     $Author: beq07716 $
21     $Revision: 1000 $
22     $Date: 2010-06-28 13:08:20 +0200 (Mon, 28 Jun 2010) $
23
24***********************************************************************************/
25
26/****************************************************************************************/
27/*                                                                                      */
28/*    Includes                                                                          */
29/*                                                                                      */
30/****************************************************************************************/
31
32#include "CompLim_private.h"
33
34/****************************************************************************************/
35/*                                                                                      */
36/* FUNCTION:                 NonLinComp_D16                                             */
37/*                                                                                      */
38/* DESCRIPTION:                                                                         */
39/*  Non-linear compression by companding. The function works on a sample by sample      */
40/*  basis by increasing the level near the zero crossing. This gives a ttrade-off       */
41/*  between THD and compression. It uses the equation:                                  */
42/*                                                                                      */
43/*        Output = Input + K * (Input - Input^2)        if Input >  0                   */
44/*               = Input + K * (Input + Input^2)      if Input <= 0                     */
45/*                                                                                      */
46/*    The value of K controls the amount of compression and as a side effect the amount */
47/*  distortion introduced. The amount of compression is signal dependent and the values */
48/*  given below are approximate.                                                        */
49/*                                                                                      */
50/*        Gain (fractional)  Gain (integer)    Compression          Pk-Pk THD           */
51/*            1.0                 32767            +6dB            16dB                 */
52/*            0.78                25559            +5dB            19dB                 */
53/*            0.6                 19661            +4dB            21dB                 */
54/*            0.41                13435            +3dB            24dB                 */
55/*            0.26                 8520            +2dB            28dB                 */
56/*            0.12                 3932            +1dB            34dB                 */
57/*            0.0                     0            +0dB            98dB                 */
58/*                                                                                      */
59/* PARAMETERS:                                                                          */
60/*    Gain            -    compression control parameter                                */
61/*    pDataIn         -    pointer to the input data buffer                             */
62/*    pDataOut        -    pointer to the output data buffer                            */
63/*    BlockLength     -    number of samples to process                                 */
64/*                                                                                      */
65/* RETURNS:                                                                             */
66/*    None                                                                              */
67/*                                                                                      */
68/* NOTES:                                                                               */
69/*                                                                                      */
70/****************************************************************************************/
71
72void NonLinComp_D16(LVM_INT16        Gain,
73                      LVM_INT16        *pDataIn,
74                    LVM_INT16        *pDataOut,
75                    LVM_INT32        BlockLength)
76{
77
78    LVM_INT16            Sample;                    /* Input samples */
79    LVM_INT32            SampleNo;                /* Sample index */
80    LVM_INT16            Temp;
81
82
83    /*
84     * Process a block of samples
85     */
86    for(SampleNo = 0; SampleNo<BlockLength; SampleNo++)
87    {
88
89        /*
90         * Read the input
91         */
92        Sample = *pDataIn;
93        pDataIn++;
94
95
96        /*
97         * Apply the compander, this compresses the signal at the expense of
98         * harmonic distortion. The amount of compression is control by the
99         * gain factor
100         */
101        if ((LVM_INT32)Sample != -32768)
102        {
103            Temp = (LVM_INT16)((Sample * Sample) >> 15);
104            if(Sample >0)
105            {
106                Sample = (LVM_INT16)(Sample + ((Gain * (Sample - Temp)) >> 15));
107            }
108            else
109            {
110                Sample = (LVM_INT16)(Sample + ((Gain * (Sample + Temp)) >> 15));
111            }
112        }
113
114
115        /*
116         * Save the output
117         */
118        *pDataOut = Sample;
119        pDataOut++;
120
121
122    }
123
124}
125
126