media/libopus/silk/control_SNR.c

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  26 ***********************************************************************/
  27
  28 #ifdef HAVE_CONFIG_H
  29 #include "config.h"
  30 #endif
  31
  32 #include "main.h"
  33 #include "tuning_parameters.h"
  34
  35 /* Control SNR of redidual quantizer */
  36 opus_int silk_control_SNR(
  37     silk_encoder_state          *psEncC,                        /* I/O  Pointer to Silk encoder state               */
  38     opus_int32                  TargetRate_bps                  /* I    Target max bitrate (bps)                    */
  39 )
  40 {
  41     opus_int k, ret = SILK_NO_ERROR;
  42     opus_int32 frac_Q6;
  43     const opus_int32 *rateTable;
  44
  45     /* Set bitrate/coding quality */
  46     TargetRate_bps = silk_LIMIT( TargetRate_bps, MIN_TARGET_RATE_BPS, MAX_TARGET_RATE_BPS );
  47     if( TargetRate_bps != psEncC->TargetRate_bps ) {
  48         psEncC->TargetRate_bps = TargetRate_bps;
  49
  50         /* If new TargetRate_bps, translate to SNR_dB value */
  51         if( psEncC->fs_kHz == 8 ) {
  52             rateTable = silk_TargetRate_table_NB;
  53         } else if( psEncC->fs_kHz == 12 ) {
  54             rateTable = silk_TargetRate_table_MB;
  55         } else {
  56             rateTable = silk_TargetRate_table_WB;
  57         }
  58
  59         /* Reduce bitrate for 10 ms modes in these calculations */
  60         if( psEncC->nb_subfr == 2 ) {
  61             TargetRate_bps -= REDUCE_BITRATE_10_MS_BPS;
  62         }
  63
  64         /* Find bitrate interval in table and interpolate */
  65         for( k = 1; k < TARGET_RATE_TAB_SZ; k++ ) {
  66             if( TargetRate_bps <= rateTable[ k ] ) {
  67                 frac_Q6 = silk_DIV32( silk_LSHIFT( TargetRate_bps - rateTable[ k - 1 ], 6 ),
  68                                                  rateTable[ k ] - rateTable[ k - 1 ] );
  69                 psEncC->SNR_dB_Q7 = silk_LSHIFT( silk_SNR_table_Q1[ k - 1 ], 6 ) + silk_MUL( frac_Q6, silk_SNR_table_Q1[ k ] - silk_SNR_table_Q1[ k - 1 ] );
  70                 break;
  71             }
  72         }
  73
  74         /* Reduce coding quality whenever LBRR is enabled, to free up some bits */
  75         if( psEncC->LBRR_enabled ) {
  76             psEncC->SNR_dB_Q7 = silk_SMLABB( psEncC->SNR_dB_Q7, 12 - psEncC->LBRR_GainIncreases, SILK_FIX_CONST( -0.25, 7 ) );
  77         }
  78     }
  79
  80     return ret;
  81 }