src/g723_24.c

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  25
  26 /*
  27  * g723_24.c
  28  *
  29  * Description:
  30  *
  31  * g723_24_encoder(), g723_24_decoder()
  32  *
  33  * These routines comprise an implementation of the CCITT G.723 24 Kbps
  34  * ADPCM coding algorithm.  Essentially, this implementation is identical to
  35  * the bit level description except for a few deviations which take advantage
  36  * of workstation attributes, such as hardware 2's complement arithmetic.
  37  *
  38  */
  39 #include "sox_i.h"
  40 #include "g711.h"
  41 #include "g72x.h"
  42
  43 /*
  44  * Maps G.723_24 code word to reconstructed scale factor normalized log
  45  * magnitude values.
  46  */
  47 static const short      _dqlntab[8] = {-2048, 135, 273, 373, 373, 273, 135, -2048};
  48
  49 /* Maps G.723_24 code word to log of scale factor multiplier. */
  50 static const short      _witab[8] = {-128, 960, 4384, 18624, 18624, 4384, 960, -128};
  51
  52 /*
  53  * Maps G.723_24 code words to a set of values whose long and short
  54  * term averages are computed and then compared to give an indication
  55  * how stationary (steady state) the signal is.
  56  */
  57 static const short      _fitab[8] = {0, 0x200, 0x400, 0xE00, 0xE00, 0x400, 0x200, 0};
  58
  59 static const short qtab_723_24[3] = {8, 218, 331};
  60
  61 /*
  62  * g723_24_encoder()
  63  *
  64  * Encodes a linear PCM, A-law or u-law input sample and returns its 3-bit code.
  65  * Returns -1 if invalid input coding value.
  66  */
  67 int g723_24_encoder(int sl, int in_coding, struct g72x_state *state_ptr)
  68 {
  69         short           sei, sezi, se, sez;     /* ACCUM */
  70         short           d;                      /* SUBTA */
  71         short           y;                      /* MIX */
  72         short           sr;                     /* ADDB */
  73         short           dqsez;                  /* ADDC */
  74         short           dq, i;
  75
  76         switch (in_coding) {    /* linearize input sample to 14-bit PCM */
  77         case AUDIO_ENCODING_ALAW:
  78                 sl = sox_alaw2linear16(sl) >> 2;
  79                 break;
  80         case AUDIO_ENCODING_ULAW:
  81                 sl = sox_ulaw2linear16(sl) >> 2;
  82                 break;
  83         case AUDIO_ENCODING_LINEAR:
  84                 sl >>= 2;               /* sl of 14-bit dynamic range */
  85                 break;
  86         default:
  87                 return (-1);
  88         }
  89
  90         sezi = predictor_zero(state_ptr);
  91         sez = sezi >> 1;
  92         sei = sezi + predictor_pole(state_ptr);
  93         se = sei >> 1;                  /* se = estimated signal */
  94
  95         d = sl - se;                    /* d = estimation diff. */
  96
  97         /* quantize prediction difference d */
  98         y = step_size(state_ptr);       /* quantizer step size */
  99         i = quantize(d, y, qtab_723_24, 3);     /* i = ADPCM code */
 100         dq = reconstruct(i & 4, _dqlntab[i], y); /* quantized diff. */
 101
 102         sr = (dq < 0) ? se - (dq & 0x3FFF) : se + dq; /* reconstructed signal */
 103
 104         dqsez = sr + sez - se;          /* pole prediction diff. */
 105
 106         update(3, y, _witab[i], _fitab[i], dq, sr, dqsez, state_ptr);
 107
 108         return (i);
 109 }
 110
 111 /*
 112  * g723_24_decoder()
 113  *
 114  * Decodes a 3-bit CCITT G.723_24 ADPCM code and returns
 115  * the resulting 16-bit linear PCM, A-law or u-law sample value.
 116  * -1 is returned if the output coding is unknown.
 117  */
 118 int g723_24_decoder(int i, int out_coding, struct g72x_state *state_ptr)
 119 {
 120         short           sezi, sei, sez, se;     /* ACCUM */
 121         short           y;                      /* MIX */
 122         short           sr;                     /* ADDB */
 123         short           dq;
 124         short           dqsez;
 125
 126         i &= 0x07;                      /* mask to get proper bits */
 127         sezi = predictor_zero(state_ptr);
 128         sez = sezi >> 1;
 129         sei = sezi + predictor_pole(state_ptr);
 130         se = sei >> 1;                  /* se = estimated signal */
 131
 132         y = step_size(state_ptr);       /* adaptive quantizer step size */
 133         dq = reconstruct(i & 0x04, _dqlntab[i], y); /* unquantize pred diff */
 134
 135         sr = (dq < 0) ? (se - (dq & 0x3FFF)) : (se + dq); /* reconst. signal */
 136
 137         dqsez = sr - se + sez;                  /* pole prediction diff. */
 138
 139         update(3, y, _witab[i], _fitab[i], dq, sr, dqsez, state_ptr);
 140
 141         switch (out_coding) {
 142         case AUDIO_ENCODING_ALAW:
 143                 return (tandem_adjust_alaw(sr, se, y, i, 4, qtab_723_24));
 144         case AUDIO_ENCODING_ULAW:
 145                 return (tandem_adjust_ulaw(sr, se, y, i, 4, qtab_723_24));
 146         case AUDIO_ENCODING_LINEAR:
 147                 return (sr << 2);       /* sr was of 14-bit dynamic range */
 148         default:
 149                 return (-1);
 150         }
 151 }