Method ApplyMelFilterBank

samples/common/src/Audio/MFCC.cpp:116–150

bool MFCC::ApplyMelFilterBank(
        std::vector<float>&                 fftVec,
        std::vector<std::vector<float>>&    melFilterBank,
        std::vector<uint32_t>&              filterBankFilterFirst,
        std::vector<uint32_t>&              filterBankFilterLast,
        std::vector<float>&                 melEnergies)
{
    const size_t numBanks = melEnergies.size();

    if (numBanks != filterBankFilterFirst.size() ||
        numBanks != filterBankFilterLast.size()) 
    {
        printf("unexpected filter bank lengths\n");
        return false;
    }

    for (size_t bin = 0; bin < numBanks; ++bin) 
    {
        auto filterBankIter = melFilterBank[bin].begin();
        auto end = melFilterBank[bin].end();
        float melEnergy = FLT_MIN;  /* Avoid log of zero at later stages */
        const uint32_t firstIndex = filterBankFilterFirst[bin];
        const uint32_t lastIndex = std::min<uint32_t>(filterBankFilterLast[bin], fftVec.size() - 1);

        for (uint32_t i = firstIndex; i <= lastIndex && filterBankIter != end; i++) 
        {
            float energyRep = sqrt(fftVec[i]);
            melEnergy += (*filterBankIter++ * energyRep);
        }

        melEnergies[bin] = melEnergy;
    }

    return true;
}

void MFCC::ConvertToLogarithmicScale(std::vector<float>& melEnergies)
{