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      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 /*    Includes                                                                          */
     21 /*                                                                                      */
     22 /****************************************************************************************/
     23 
     24 #include "CompLim_private.h"
     25 
     26 /****************************************************************************************/
     27 /*                                                                                      */
     28 /* FUNCTION:                 NonLinComp_D16                                             */
     29 /*                                                                                      */
     30 /* DESCRIPTION:                                                                         */
     31 /*  Non-linear compression by companding. The function works on a sample by sample      */
     32 /*  basis by increasing the level near the zero crossing. This gives a ttrade-off       */
     33 /*  between THD and compression. It uses the equation:                                  */
     34 /*                                                                                      */
     35 /*        Output = Input + K * (Input - Input^2)        if Input >  0                   */
     36 /*               = Input + K * (Input + Input^2)      if Input <= 0                     */
     37 /*                                                                                      */
     38 /*    The value of K controls the amount of compression and as a side effect the amount */
     39 /*  distortion introduced. The amount of compression is signal dependent and the values */
     40 /*  given below are approximate.                                                        */
     41 /*                                                                                      */
     42 /*        Gain (fractional)  Gain (integer)    Compression          Pk-Pk THD           */
     43 /*            1.0                 32767            +6dB            16dB                 */
     44 /*            0.78                25559            +5dB            19dB                 */
     45 /*            0.6                 19661            +4dB            21dB                 */
     46 /*            0.41                13435            +3dB            24dB                 */
     47 /*            0.26                 8520            +2dB            28dB                 */
     48 /*            0.12                 3932            +1dB            34dB                 */
     49 /*            0.0                     0            +0dB            98dB                 */
     50 /*                                                                                      */
     51 /* PARAMETERS:                                                                          */
     52 /*    Gain            -    compression control parameter                                */
     53 /*    pDataIn         -    pointer to the input data buffer                             */
     54 /*    pDataOut        -    pointer to the output data buffer                            */
     55 /*    BlockLength     -    number of samples to process                                 */
     56 /*                                                                                      */
     57 /* RETURNS:                                                                             */
     58 /*    None                                                                              */
     59 /*                                                                                      */
     60 /* NOTES:                                                                               */
     61 /*                                                                                      */
     62 /****************************************************************************************/
     63 
     64 void NonLinComp_D16(LVM_INT16        Gain,
     65                       LVM_INT16        *pDataIn,
     66                     LVM_INT16        *pDataOut,
     67                     LVM_INT32        BlockLength)
     68 {
     69 
     70     LVM_INT16            Sample;                    /* Input samples */
     71     LVM_INT32            SampleNo;                /* Sample index */
     72     LVM_INT16            Temp;
     73 
     74 
     75     /*
     76      * Process a block of samples
     77      */
     78     for(SampleNo = 0; SampleNo<BlockLength; SampleNo++)
     79     {
     80 
     81         /*
     82          * Read the input
     83          */
     84         Sample = *pDataIn;
     85         pDataIn++;
     86 
     87 
     88         /*
     89          * Apply the compander, this compresses the signal at the expense of
     90          * harmonic distortion. The amount of compression is control by the
     91          * gain factor
     92          */
     93         if ((LVM_INT32)Sample != -32768)
     94         {
     95             Temp = (LVM_INT16)((Sample * Sample) >> 15);
     96             if(Sample >0)
     97             {
     98                 Sample = (LVM_INT16)(Sample + ((Gain * (Sample - Temp)) >> 15));
     99             }
    100             else
    101             {
    102                 Sample = (LVM_INT16)(Sample + ((Gain * (Sample + Temp)) >> 15));
    103             }
    104         }
    105 
    106 
    107         /*
    108          * Save the output
    109          */
    110         *pDataOut = Sample;
    111         pDataOut++;
    112 
    113 
    114     }
    115 
    116 }
    117 
    118