语音识别入门第五节：基于GMM-HMM的语音识别系统（实战篇）

练习基础代码（包括音频文件、音频文件读取代码、预加重代码、分帧加窗代码、快速傅里叶变换代码）可从Github中获取，链接如下：GitHub - nwpuaslp/ASR_Course。

本节理论笔记见：语音识别入门第五节：基于GMM-HMM的语音识别系统

lib_vit.c中需要添加代码如下：

  int startState = graph.get_start_state(); //to get the start state
  for (int frmIdx = 0; frmIdx < frmCnt; frmIdx++){ //frame cycle
    for(int stateIdx = 0; stateIdx < stateCnt; stateIdx++) {//state cycle
      if(frmIdx == 0){
        chart(frmIdx, startState).assign(0, -1); //set the forward probability to 0 and Arc ID to -1
        stateIdx = startState;
      }
      int arcCnt = graph.get_arc_count(stateIdx); // get the arc number
      int arcId = graph.get_first_arc_id(stateIdx); //the frist arc id is -1
      for(int arcIdx = 0; arcIdx < arcCnt; arcIdx++){ //arc cycle
        int curArcId = arcId; //Current arc id=-1
        Arc arc; //Arc class instantiation
        arcId = graph.get_arc(arcId, arc);
        int dstState = arc.get_dst_state(); //Jump to the next state
        int gmmIndex = arc.get_gmm(); //get GMM ID
        double logPorb = chart(frmIdx, stateIdx).get_log_prob() + gmmProbs(frmIdx, gmmIndex) + arc.get_log_prob();
        if(logPorb > chart(frmIdx + 1, dstState).get_log_prob()){
          chart(frmIdx + 1, dstState).assign(logPorb, curArcId);
        }
      }
      if(frmIdx == 0)
        break;
    }
  } 

gmm_util.C中需要添加代码如下:

  m_gaussCounts[gaussIdx] += posterior;
  for(int dimIdx = 0; dimIdx < dimCnt; dimIdx++){
    m_gaussStats1(gaussIdx, dimIdx) += posterior * feats[dimIdx];
    m_gaussStats2(gaussIdx, dimIdx) += posterior * feats[dimIdx] * feats[dimIdx];
  }

  for(int gaussIdx = 0; gaussIdx < gaussCnt; gaussIdx++){
    for(int dimIdx = 0; dimIdx < dimCnt; dimIdx++){
      double newMean = m_gaussStats1(gaussIdx, dimIdx) / m_gaussCounts[gaussIdx];
      double newVar = (m_gaussStats2(gaussIdx, dimIdx) - 2 * m_gaussStats1(gaussIdx, dimIdx) * newMean + newMean * newMean * m_gaussCounts[gaussIdx]) / m_gaussCounts[gaussIdx];
      m_gmmSet.set_gaussian_mean(gaussIdx, dimIdx, newMean);
      m_gmmSet.set_gaussian_var(gaussIdx, dimIdx, newVar);
    }
  }

lab2_fb.C中需要添加代码如下：

  int startState = graph.get_start_state();
  for(int frmIdx = 0; frmIdx < frmCnt; frmIdx++){
    for(int stateIdx = 0; stateIdx < stateCnt; stateIdx++){
      if(frmIdx == 0){
        chart(frmIdx, startState).set_forw_log_prob(0);
      }
      int arcCnt = graph.get_arc_count(stateIdx);
      int arcId = graph.get_first_arc_id(stateIdx);
      for(int arcIdx = 0; arcIdx < arcCnt; arcIdx++){
        Arc arc;
        arcId = graph.get_arc(arcId, arc);
        int dstState = arc.get_dst_state();
        int gmmIndex = arc.get_gmm();
        double logProb = chart(frmIdx, stateIdx).get_forw_log_prob() + gmmProbs(frmIdx, gmmIndex) + arc.get_log_prob();
        vector logProbList = {logProb, chart(frmIdx + 1, dstState).get_forw_log_prob()};
        logProb = add_log_probs(logProbList);
        chart(frmIdx + 1, dstState).set_forw_log_prob(logProb);
      }
    }
  }

  for(int frmIdx = frmCnt; frmIdx > 0; --frmIdx){
    for(int stateIdx = 0; stateIdx < stateCnt; ++ stateIdx){
      int arcCnt = graph.get_arc_count(stateIdx);
      int arcId = graph.get_first_arc_id(stateIdx);
      for(int arcIdx = 0; arcIdx < arcCnt; ++arcIdx){
        Arc arc;
        arcId = graph.get_arc(arcId, arc);
        int dstState = arc.get_dst_state();
        double logProb = chart(frmIdx - 1, stateIdx).get_forw_log_prob() + 
          arc.get_log_prob() + 
          gmmProbs(frmIdx - 1, arc.get_gmm()) + 
          chart(frmIdx, dstState).get_back_log_prob();
        gmmCountList.push_back(GmmCount(arc.get_gmm(), frmIdx - 1, exp(logProb - uttLogProb)));
      }
    }
  }