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      1 /*
      2  *  Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
      3  *
      4  *  Use of this source code is governed by a BSD-style license
      5  *  that can be found in the LICENSE file in the root of the source
      6  *  tree. An additional intellectual property rights grant can be found
      7  *  in the file PATENTS.  All contributing project authors may
      8  *  be found in the AUTHORS file in the root of the source tree.
      9  */
     10 
     11 #include "webrtc/common_audio/vad/vad_sp.h"
     12 
     13 #include <assert.h>
     14 
     15 #include "webrtc/common_audio/signal_processing/include/signal_processing_library.h"
     16 #include "webrtc/common_audio/vad/vad_core.h"
     17 #include "webrtc/typedefs.h"
     18 
     19 // Allpass filter coefficients, upper and lower, in Q13.
     20 // Upper: 0.64, Lower: 0.17.
     21 static const int16_t kAllPassCoefsQ13[2] = { 5243, 1392 };  // Q13.
     22 static const int16_t kSmoothingDown = 6553;  // 0.2 in Q15.
     23 static const int16_t kSmoothingUp = 32439;  // 0.99 in Q15.
     24 
     25 // TODO(bjornv): Move this function to vad_filterbank.c.
     26 // Downsampling filter based on splitting filter and allpass functions.
     27 void WebRtcVad_Downsampling(const int16_t* signal_in,
     28                             int16_t* signal_out,
     29                             int32_t* filter_state,
     30                             size_t in_length) {
     31   int16_t tmp16_1 = 0, tmp16_2 = 0;
     32   int32_t tmp32_1 = filter_state[0];
     33   int32_t tmp32_2 = filter_state[1];
     34   size_t n = 0;
     35   // Downsampling by 2 gives half length.
     36   size_t half_length = (in_length >> 1);
     37 
     38   // Filter coefficients in Q13, filter state in Q0.
     39   for (n = 0; n < half_length; n++) {
     40     // All-pass filtering upper branch.
     41     tmp16_1 = (int16_t) ((tmp32_1 >> 1) +
     42         ((kAllPassCoefsQ13[0] * *signal_in) >> 14));
     43     *signal_out = tmp16_1;
     44     tmp32_1 = (int32_t)(*signal_in++) - ((kAllPassCoefsQ13[0] * tmp16_1) >> 12);
     45 
     46     // All-pass filtering lower branch.
     47     tmp16_2 = (int16_t) ((tmp32_2 >> 1) +
     48         ((kAllPassCoefsQ13[1] * *signal_in) >> 14));
     49     *signal_out++ += tmp16_2;
     50     tmp32_2 = (int32_t)(*signal_in++) - ((kAllPassCoefsQ13[1] * tmp16_2) >> 12);
     51   }
     52   // Store the filter states.
     53   filter_state[0] = tmp32_1;
     54   filter_state[1] = tmp32_2;
     55 }
     56 
     57 // Inserts |feature_value| into |low_value_vector|, if it is one of the 16
     58 // smallest values the last 100 frames. Then calculates and returns the median
     59 // of the five smallest values.
     60 int16_t WebRtcVad_FindMinimum(VadInstT* self,
     61                               int16_t feature_value,
     62                               int channel) {
     63   int i = 0, j = 0;
     64   int position = -1;
     65   // Offset to beginning of the 16 minimum values in memory.
     66   const int offset = (channel << 4);
     67   int16_t current_median = 1600;
     68   int16_t alpha = 0;
     69   int32_t tmp32 = 0;
     70   // Pointer to memory for the 16 minimum values and the age of each value of
     71   // the |channel|.
     72   int16_t* age = &self->index_vector[offset];
     73   int16_t* smallest_values = &self->low_value_vector[offset];
     74 
     75   assert(channel < kNumChannels);
     76 
     77   // Each value in |smallest_values| is getting 1 loop older. Update |age|, and
     78   // remove old values.
     79   for (i = 0; i < 16; i++) {
     80     if (age[i] != 100) {
     81       age[i]++;
     82     } else {
     83       // Too old value. Remove from memory and shift larger values downwards.
     84       for (j = i; j < 16; j++) {
     85         smallest_values[j] = smallest_values[j + 1];
     86         age[j] = age[j + 1];
     87       }
     88       age[15] = 101;
     89       smallest_values[15] = 10000;
     90     }
     91   }
     92 
     93   // Check if |feature_value| is smaller than any of the values in
     94   // |smallest_values|. If so, find the |position| where to insert the new value
     95   // (|feature_value|).
     96   if (feature_value < smallest_values[7]) {
     97     if (feature_value < smallest_values[3]) {
     98       if (feature_value < smallest_values[1]) {
     99         if (feature_value < smallest_values[0]) {
    100           position = 0;
    101         } else {
    102           position = 1;
    103         }
    104       } else if (feature_value < smallest_values[2]) {
    105         position = 2;
    106       } else {
    107         position = 3;
    108       }
    109     } else if (feature_value < smallest_values[5]) {
    110       if (feature_value < smallest_values[4]) {
    111         position = 4;
    112       } else {
    113         position = 5;
    114       }
    115     } else if (feature_value < smallest_values[6]) {
    116       position = 6;
    117     } else {
    118       position = 7;
    119     }
    120   } else if (feature_value < smallest_values[15]) {
    121     if (feature_value < smallest_values[11]) {
    122       if (feature_value < smallest_values[9]) {
    123         if (feature_value < smallest_values[8]) {
    124           position = 8;
    125         } else {
    126           position = 9;
    127         }
    128       } else if (feature_value < smallest_values[10]) {
    129         position = 10;
    130       } else {
    131         position = 11;
    132       }
    133     } else if (feature_value < smallest_values[13]) {
    134       if (feature_value < smallest_values[12]) {
    135         position = 12;
    136       } else {
    137         position = 13;
    138       }
    139     } else if (feature_value < smallest_values[14]) {
    140       position = 14;
    141     } else {
    142       position = 15;
    143     }
    144   }
    145 
    146   // If we have detected a new small value, insert it at the correct position
    147   // and shift larger values up.
    148   if (position > -1) {
    149     for (i = 15; i > position; i--) {
    150       smallest_values[i] = smallest_values[i - 1];
    151       age[i] = age[i - 1];
    152     }
    153     smallest_values[position] = feature_value;
    154     age[position] = 1;
    155   }
    156 
    157   // Get |current_median|.
    158   if (self->frame_counter > 2) {
    159     current_median = smallest_values[2];
    160   } else if (self->frame_counter > 0) {
    161     current_median = smallest_values[0];
    162   }
    163 
    164   // Smooth the median value.
    165   if (self->frame_counter > 0) {
    166     if (current_median < self->mean_value[channel]) {
    167       alpha = kSmoothingDown;  // 0.2 in Q15.
    168     } else {
    169       alpha = kSmoothingUp;  // 0.99 in Q15.
    170     }
    171   }
    172   tmp32 = (alpha + 1) * self->mean_value[channel];
    173   tmp32 += (WEBRTC_SPL_WORD16_MAX - alpha) * current_median;
    174   tmp32 += 16384;
    175   self->mean_value[channel] = (int16_t) (tmp32 >> 15);
    176 
    177   return self->mean_value[channel];
    178 }
    179