embdrv/lc3/Decoder/PacketLossConcealment.cpp

/*
 * PacketLossConcealment.cpp
 *
 * Copyright 2021 HIMSA II K/S - www.himsa.com. Represented by EHIMA -
 * www.ehima.com
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "PacketLossConcealment.hpp"

namespace Lc3Dec {

PacketLossConcealment::PacketLossConcealment(uint16_t NE_)
    : NE(NE_),
      plc_seed(24607),  // this initialization need not be done every frame as
                        // clarified by Errata 15114
      nbLostCmpt(0),
      alpha(1),
      X_hat_lastGood(nullptr) {
  X_hat_lastGood = new double[NE];
  for (uint16_t k = 0; k < NE; k++) {
    X_hat_lastGood[k] = 0.0;
  }
}

PacketLossConcealment::~PacketLossConcealment() { delete[] X_hat_lastGood; }

void PacketLossConcealment::run(uint8_t BEC_detect, double* X_hat,
                                int16_t& ltpf_active) {
  // Appendix B. Packet Loss Concealment   (d09r02_F2F)
  if (0 == BEC_detect) {
    nbLostCmpt = 0;
    alpha = 1;
    for (uint16_t k = 0; k < NE; k++) {
      X_hat_lastGood[k] = X_hat[k];
    }
  } else {
    ltpf_active = 0;  // errata 15097 implemented

    if (nbLostCmpt < 0xFF) {
      nbLostCmpt++;
    }

    // Note: from (d09r02_F2F) its is not perfectly clear,
    //   whether alpha is modified before or after applying
    //   it to the spectrum -> we may have to check the
    //   given implementation with the LC3.exe reference
    if (nbLostCmpt >= 8) {
      alpha = 0.85 * alpha;
    } else if (nbLostCmpt >= 4) {
      alpha = 0.9 * alpha;
    }

    for (uint16_t k = 0; k < NE; k++) {
      plc_seed = (16831 + plc_seed * 12821) & 0xFFFF;
      if (plc_seed < 0x8000) {
        X_hat[k] = alpha * X_hat_lastGood[k];
      } else {
        X_hat[k] = -alpha * X_hat_lastGood[k];
      }
    }
  }
}

void PacketLossConcealment::registerDatapoints(DatapointContainer* datapoints) {
  if (nullptr != datapoints) {
    datapoints->addDatapoint("X_hat_lastGood", &X_hat_lastGood[0],
                             sizeof(double) * NE);
  }
}

}  // namespace Lc3Dec