diff --git a/source/use_case/noise_reduction/src/RNNoiseProcess.cc b/source/use_case/noise_reduction/src/RNNoiseProcess.cc
new file mode 100644
index 0000000..d9a7b35
--- /dev/null
+++ b/source/use_case/noise_reduction/src/RNNoiseProcess.cc
@@ -0,0 +1,888 @@
+/*
+ * Copyright (c) 2021 Arm Limited. All rights reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * 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 "RNNoiseProcess.hpp"
+#include <algorithm>
+#include <cmath>
+#include <cstring>
+
+namespace arm {
+namespace app {
+namespace rnn {
+
+#define VERIFY(x)                                   \
+do {                                                \
+    if (!(x)) {                                     \
+        printf_err("Assert failed:" #x "\n");       \
+        exit(1);                                    \
+    }                                               \
+} while(0)
+
+RNNoiseProcess::RNNoiseProcess() :
+        m_halfWindow(FRAME_SIZE, 0),
+        m_dctTable(NB_BANDS * NB_BANDS),
+        m_analysisMem(FRAME_SIZE, 0),
+        m_cepstralMem(CEPS_MEM, vec1D32F(NB_BANDS, 0)),
+        m_memId{0},
+        m_synthesisMem(FRAME_SIZE, 0),
+        m_pitchBuf(PITCH_BUF_SIZE, 0),
+        m_lastGain{0.0},
+        m_lastPeriod{0},
+        m_memHpX{},
+        m_lastGVec(NB_BANDS, 0)
+{
+    constexpr uint32_t numFFt = 2 * FRAME_SIZE;
+    static_assert(numFFt != 0, "Num FFT can't be 0");
+
+    math::MathUtils::FftInitF32(numFFt, this->m_fftInstReal, FftType::real);
+    math::MathUtils::FftInitF32(numFFt, this->m_fftInstCmplx, FftType::complex);
+    this->InitTables();
+}
+
+void RNNoiseProcess::PreprocessFrame(const float*   audioData,
+                                     const size_t   audioLen,
+                                     FrameFeatures& features)
+{
+    /* Note audioWindow is modified in place */
+    const arrHp aHp {-1.99599, 0.99600 };
+    const arrHp bHp {-2.00000, 1.00000 };
+
+    vec1D32F audioWindow{audioData, audioData + audioLen};
+
+    this->BiQuad(bHp, aHp, this->m_memHpX, audioWindow);
+    this->ComputeFrameFeatures(audioWindow, features);
+}
+
+void RNNoiseProcess::PostProcessFrame(vec1D32F& modelOutput, FrameFeatures& features, vec1D32F& outFrame)
+{
+    std::vector<float> g = modelOutput;  /* Gain values. */
+    std::vector<float> gf(FREQ_SIZE, 0);
+
+    if (!features.m_silence) {
+        PitchFilter(features, g);
+        for (size_t i = 0; i < NB_BANDS; i++) {
+            float alpha = .6f;
+            g[i] = std::max(g[i], alpha * m_lastGVec[i]);
+            m_lastGVec[i] = g[i];
+        }
+        InterpBandGain(gf, g);
+        for (size_t i = 0; i < FREQ_SIZE; i++) {
+            features.m_fftX[2 * i] *= gf[i];  /* Real. */
+            features.m_fftX[2 * i + 1] *= gf[i];  /*imaginary. */
+
+        }
+
+    }
+
+    FrameSynthesis(outFrame, features.m_fftX);
+}
+
+void RNNoiseProcess::InitTables()
+{
+    constexpr float pi = M_PI;
+    constexpr float halfPi = M_PI / 2;
+    constexpr float halfPiOverFrameSz = halfPi/FRAME_SIZE;
+
+    for (uint32_t i = 0; i < FRAME_SIZE; i++) {
+        const float sinVal = math::MathUtils::SineF32(halfPiOverFrameSz * (i + 0.5f));
+        m_halfWindow[i] = math::MathUtils::SineF32(halfPi * sinVal * sinVal);
+    }
+
+    for (uint32_t i = 0; i < NB_BANDS; i++) {
+        for (uint32_t j = 0; j < NB_BANDS; j++) {
+            m_dctTable[i * NB_BANDS + j] = math::MathUtils::CosineF32((i + 0.5f) * j * pi / NB_BANDS);
+        }
+        m_dctTable[i * NB_BANDS] *= math::MathUtils::SqrtF32(0.5f);
+    }
+}
+
+void RNNoiseProcess::BiQuad(
+        const arrHp& bHp,
+        const arrHp& aHp,
+        arrHp& memHpX,
+        vec1D32F& audioWindow)
+{
+    for (float& audioElement : audioWindow) {
+        const auto xi = audioElement;
+        const auto yi = audioElement + memHpX[0];
+        memHpX[0] = memHpX[1] + (bHp[0] * xi - aHp[0] * yi);
+        memHpX[1] = (bHp[1] * xi - aHp[1] * yi);
+        audioElement = yi;
+    }
+}
+
+void RNNoiseProcess::ComputeFrameFeatures(vec1D32F& audioWindow,
+                                          FrameFeatures& features)
+{
+    this->FrameAnalysis(audioWindow,
+                        features.m_fftX,
+                        features.m_Ex,
+                        this->m_analysisMem);
+
+    float E = 0.0;
+
+    vec1D32F Ly(NB_BANDS, 0);
+    vec1D32F p(WINDOW_SIZE, 0);
+    vec1D32F pitchBuf(PITCH_BUF_SIZE >> 1, 0);
+
+    VERIFY(PITCH_BUF_SIZE >= this->m_pitchBuf.size());
+    std::copy_n(this->m_pitchBuf.begin() + FRAME_SIZE,
+                PITCH_BUF_SIZE - FRAME_SIZE,
+                this->m_pitchBuf.begin());
+
+    VERIFY(FRAME_SIZE <= audioWindow.size() && PITCH_BUF_SIZE > FRAME_SIZE);
+    std::copy_n(audioWindow.begin(),
+                FRAME_SIZE,
+                this->m_pitchBuf.begin() + PITCH_BUF_SIZE - FRAME_SIZE);
+
+    this->PitchDownsample(pitchBuf, PITCH_BUF_SIZE);
+
+    VERIFY(pitchBuf.size() > PITCH_MAX_PERIOD/2);
+    vec1D32F xLp(pitchBuf.size() - PITCH_MAX_PERIOD/2, 0);
+    std::copy_n(pitchBuf.begin() + PITCH_MAX_PERIOD/2, xLp.size(), xLp.begin());
+
+    int pitchIdx = this->PitchSearch(xLp, pitchBuf,
+            PITCH_FRAME_SIZE, (PITCH_MAX_PERIOD - (3*PITCH_MIN_PERIOD)));
+
+    pitchIdx = this->RemoveDoubling(
+                pitchBuf,
+                PITCH_MAX_PERIOD,
+                PITCH_MIN_PERIOD,
+                PITCH_FRAME_SIZE,
+                PITCH_MAX_PERIOD - pitchIdx);
+
+    size_t stIdx = PITCH_BUF_SIZE - WINDOW_SIZE - pitchIdx;
+    VERIFY((static_cast<int>(PITCH_BUF_SIZE) - static_cast<int>(WINDOW_SIZE) - pitchIdx) >= 0);
+    std::copy_n(this->m_pitchBuf.begin() + stIdx, WINDOW_SIZE, p.begin());
+
+    this->ApplyWindow(p);
+    this->ForwardTransform(p, features.m_fftP);
+    this->ComputeBandEnergy(features.m_fftP, features.m_Ep);
+    this->ComputeBandCorr(features.m_fftX, features.m_fftP, features.m_Exp);
+
+    for (uint32_t i = 0 ; i < NB_BANDS; ++i) {
+        features.m_Exp[i] /= math::MathUtils::SqrtF32(
+            0.001f + features.m_Ex[i] * features.m_Ep[i]);
+    }
+
+    vec1D32F dctVec(NB_BANDS, 0);
+    this->DCT(features.m_Exp, dctVec);
+
+    features.m_featuresVec = vec1D32F (NB_FEATURES, 0);
+    for (uint32_t i = 0; i < NB_DELTA_CEPS; ++i) {
+        features.m_featuresVec[NB_BANDS + 2*NB_DELTA_CEPS + i] = dctVec[i];
+    }
+
+    features.m_featuresVec[NB_BANDS + 2*NB_DELTA_CEPS] -= 1.3;
+    features.m_featuresVec[NB_BANDS + 2*NB_DELTA_CEPS + 1] -= 0.9;
+    features.m_featuresVec[NB_BANDS + 3*NB_DELTA_CEPS] = 0.01 * (static_cast<int>(pitchIdx) - 300);
+
+    float logMax = -2.f;
+    float follow = -2.f;
+    for (uint32_t i = 0; i < NB_BANDS; ++i) {
+        Ly[i] = log10f(1e-2f + features.m_Ex[i]);
+        Ly[i] = std::max<float>(logMax - 7, std::max<float>(follow - 1.5, Ly[i]));
+        logMax = std::max<float>(logMax, Ly[i]);
+        follow = std::max<float>(follow - 1.5, Ly[i]);
+        E += features.m_Ex[i];
+    }
+
+    /* If there's no audio avoid messing up the state. */
+    features.m_silence = true;
+    if (E < 0.04) {
+        return;
+    } else {
+        features.m_silence = false;
+    }
+
+    this->DCT(Ly, features.m_featuresVec);
+    features.m_featuresVec[0] -= 12.0;
+    features.m_featuresVec[1] -= 4.0;
+
+    VERIFY(CEPS_MEM > 2);
+    uint32_t stIdx1 = this->m_memId < 1 ? CEPS_MEM + this->m_memId - 1 : this->m_memId - 1;
+    uint32_t stIdx2 = this->m_memId < 2 ? CEPS_MEM + this->m_memId - 2 : this->m_memId - 2;
+
+    auto ceps1 = this->m_cepstralMem[stIdx1];
+    auto ceps2 = this->m_cepstralMem[stIdx2];
+
+    /* Ceps 0 */
+    for (uint32_t i = 0; i < NB_BANDS; ++i) {
+        this->m_cepstralMem[this->m_memId][i] = features.m_featuresVec[i];
+    }
+
+    for (uint32_t i = 0; i < NB_DELTA_CEPS; ++i) {
+        features.m_featuresVec[i] = this->m_cepstralMem[this->m_memId][i] + ceps1[i] + ceps2[i];
+        features.m_featuresVec[NB_BANDS + i] = this->m_cepstralMem[this->m_memId][i] - ceps2[i];
+        features.m_featuresVec[NB_BANDS + NB_DELTA_CEPS + i] =
+                this->m_cepstralMem[this->m_memId][i] - 2 * ceps1[i] + ceps2[i];
+    }
+
+    /* Spectral variability features. */
+    this->m_memId += 1;
+    if (this->m_memId == CEPS_MEM) {
+        this->m_memId = 0;
+    }
+
+    float specVariability = 0.f;
+
+    VERIFY(this->m_cepstralMem.size() >= CEPS_MEM);
+    for (size_t i = 0; i < CEPS_MEM; ++i) {
+        float minDist = 1e15;
+        for (size_t j = 0; j < CEPS_MEM; ++j) {
+            float dist = 0.f;
+            for (size_t k = 0; k < NB_BANDS; ++k) {
+                VERIFY(this->m_cepstralMem[i].size() >= NB_BANDS);
+                auto tmp = this->m_cepstralMem[i][k] - this->m_cepstralMem[j][k];
+                dist += tmp * tmp;
+            }
+
+            if (j != i) {
+                minDist = std::min<float>(minDist, dist);
+            }
+        }
+        specVariability += minDist;
+    }
+
+    VERIFY(features.m_featuresVec.size() >= NB_BANDS + 3 * NB_DELTA_CEPS + 1);
+    features.m_featuresVec[NB_BANDS + 3 * NB_DELTA_CEPS + 1] = specVariability / CEPS_MEM - 2.1;
+}
+
+void RNNoiseProcess::FrameAnalysis(
+    const vec1D32F& audioWindow,
+    vec1D32F& fft,
+    vec1D32F& energy,
+    vec1D32F& analysisMem)
+{
+    vec1D32F x(WINDOW_SIZE, 0);
+
+    /* Move old audio down and populate end with latest audio window. */
+    VERIFY(x.size() >= FRAME_SIZE && analysisMem.size() >= FRAME_SIZE);
+    VERIFY(audioWindow.size() >= FRAME_SIZE);
+
+    std::copy_n(analysisMem.begin(), FRAME_SIZE, x.begin());
+    std::copy_n(audioWindow.begin(), x.size() - FRAME_SIZE, x.begin() + FRAME_SIZE);
+    std::copy_n(audioWindow.begin(), FRAME_SIZE, analysisMem.begin());
+
+    this->ApplyWindow(x);
+
+    /* Calculate FFT. */
+    ForwardTransform(x, fft);
+
+    /* Compute band energy. */
+    ComputeBandEnergy(fft, energy);
+}
+
+void RNNoiseProcess::ApplyWindow(vec1D32F& x)
+{
+    if (WINDOW_SIZE != x.size()) {
+        printf_err("Invalid size for vector to be windowed\n");
+        return;
+    }
+
+    VERIFY(this->m_halfWindow.size() >= FRAME_SIZE);
+
+    /* Multiply input by sinusoidal function. */
+    for (size_t i = 0; i < FRAME_SIZE; i++) {
+        x[i] *= this->m_halfWindow[i];
+        x[WINDOW_SIZE - 1 - i] *= this->m_halfWindow[i];
+    }
+}
+
+void RNNoiseProcess::ForwardTransform(
+    vec1D32F& x,
+    vec1D32F& fft)
+{
+    /* The input vector can be modified by the fft function. */
+    fft.reserve(x.size() + 2);
+    fft.resize(x.size() + 2, 0);
+    math::MathUtils::FftF32(x, fft, this->m_fftInstReal);
+
+    /* Normalise. */
+    for (auto& f : fft) {
+        f /= this->m_fftInstReal.m_fftLen;
+    }
+
+    /* Place the last freq element correctly */
+    fft[fft.size()-2] = fft[1];
+    fft[1] = 0;
+
+    /* NOTE: We don't truncate out FFT vector as it already contains only the
+     * first half of the FFT's. The conjugates are not present. */
+}
+
+void RNNoiseProcess::ComputeBandEnergy(const vec1D32F& fftX, vec1D32F& bandE)
+{
+    bandE = vec1D32F(NB_BANDS, 0);
+
+    VERIFY(this->m_eband5ms.size() >= NB_BANDS);
+    for (uint32_t i = 0; i < NB_BANDS - 1; i++) {
+        const auto bandSize = (this->m_eband5ms[i + 1] - this->m_eband5ms[i])
+                              << FRAME_SIZE_SHIFT;
+
+        for (uint32_t j = 0; j < bandSize; j++) {
+            const auto frac = static_cast<float>(j) / bandSize;
+            const auto idx = (this->m_eband5ms[i] << FRAME_SIZE_SHIFT) + j;
+
+            auto tmp = fftX[2 * idx] * fftX[2 * idx]; /* Real part */
+            tmp += fftX[2 * idx + 1] * fftX[2 * idx + 1]; /* Imaginary part */
+
+            bandE[i] += (1 - frac) * tmp;
+            bandE[i + 1] += frac * tmp;
+        }
+    }
+    bandE[0] *= 2;
+    bandE[NB_BANDS - 1] *= 2;
+}
+
+void RNNoiseProcess::ComputeBandCorr(const vec1D32F& X, const vec1D32F& P, vec1D32F& bandC)
+{
+    bandC = vec1D32F(NB_BANDS, 0);
+    VERIFY(this->m_eband5ms.size() >= NB_BANDS);
+
+    for (uint32_t i = 0; i < NB_BANDS - 1; i++) {
+        const auto bandSize = (this->m_eband5ms[i + 1] - this->m_eband5ms[i]) << FRAME_SIZE_SHIFT;
+
+        for (uint32_t j = 0; j < bandSize; j++) {
+            const auto frac = static_cast<float>(j) / bandSize;
+            const auto idx = (this->m_eband5ms[i] << FRAME_SIZE_SHIFT) + j;
+
+            auto tmp = X[2 * idx] * P[2 * idx]; /* Real part */
+            tmp += X[2 * idx + 1] * P[2 * idx + 1]; /* Imaginary part */
+
+            bandC[i] += (1 - frac) * tmp;
+            bandC[i + 1] += frac * tmp;
+        }
+    }
+    bandC[0] *= 2;
+    bandC[NB_BANDS - 1] *= 2;
+}
+
+void RNNoiseProcess::DCT(vec1D32F& input, vec1D32F& output)
+{
+    VERIFY(this->m_dctTable.size() >= NB_BANDS * NB_BANDS);
+    for (uint32_t i = 0; i < NB_BANDS; ++i) {
+        float sum = 0;
+
+        for (uint32_t j = 0, k = 0; j < NB_BANDS; ++j, k += NB_BANDS) {
+            sum += input[j] * this->m_dctTable[k + i];
+        }
+        output[i] = sum * math::MathUtils::SqrtF32(2.0/22);
+    }
+}
+
+void RNNoiseProcess::PitchDownsample(vec1D32F& pitchBuf, size_t pitchBufSz) {
+    for (size_t i = 1; i < (pitchBufSz >> 1); ++i) {
+        pitchBuf[i] = 0.5 * (
+                        0.5 * (this->m_pitchBuf[2 * i - 1] + this->m_pitchBuf[2 * i + 1])
+                            + this->m_pitchBuf[2 * i]);
+    }
+
+    pitchBuf[0] = 0.5*(0.5*(this->m_pitchBuf[1]) + this->m_pitchBuf[0]);
+
+    vec1D32F ac(5, 0);
+    size_t numLags = 4;
+
+    this->AutoCorr(pitchBuf, ac, numLags, pitchBufSz >> 1);
+
+    /* Noise floor -40db */
+    ac[0] *= 1.0001;
+
+    /* Lag windowing. */
+    for (size_t i = 1; i < numLags + 1; ++i) {
+        ac[i] -= ac[i] * (0.008 * i) * (0.008 * i);
+    }
+
+    vec1D32F lpc(numLags, 0);
+    this->LPC(ac, numLags, lpc);
+
+    float tmp = 1.0;
+    for (size_t i = 0; i < numLags; ++i) {
+        tmp = 0.9f * tmp;
+        lpc[i] = lpc[i] * tmp;
+    }
+
+    vec1D32F lpc2(numLags + 1, 0);
+    float c1 = 0.8;
+
+    /* Add a zero. */
+    lpc2[0] = lpc[0] + 0.8;
+    lpc2[1] = lpc[1] + (c1 * lpc[0]);
+    lpc2[2] = lpc[2] + (c1 * lpc[1]);
+    lpc2[3] = lpc[3] + (c1 * lpc[2]);
+    lpc2[4] = (c1 * lpc[3]);
+
+    this->Fir5(lpc2, pitchBufSz >> 1, pitchBuf);
+}
+
+int RNNoiseProcess::PitchSearch(vec1D32F& xLp, vec1D32F& y, uint32_t len, uint32_t maxPitch) {
+    uint32_t lag = len + maxPitch;
+    vec1D32F xLp4(len >> 2, 0);
+    vec1D32F yLp4(lag >> 2, 0);
+    vec1D32F xCorr(maxPitch >> 1, 0);
+
+    /* Downsample by 2 again. */
+    for (size_t j = 0; j < (len >> 2); ++j) {
+        xLp4[j] = xLp[2*j];
+    }
+    for (size_t j = 0; j < (lag >> 2); ++j) {
+        yLp4[j] = y[2*j];
+    }
+
+    this->PitchXCorr(xLp4, yLp4, xCorr, len >> 2, maxPitch >> 2);
+
+    /* Coarse search with 4x decimation. */
+    arrHp bestPitch = this->FindBestPitch(xCorr, yLp4, len >> 2, maxPitch >> 2);
+
+    /* Finer search with 2x decimation. */
+    const int maxIdx = (maxPitch >> 1);
+    for (int i = 0; i < maxIdx; ++i) {
+        xCorr[i] = 0;
+        if (std::abs(i - 2*bestPitch[0]) > 2 and std::abs(i - 2*bestPitch[1]) > 2) {
+            continue;
+        }
+        float sum = 0;
+        for (size_t j = 0; j < len >> 1; ++j) {
+            sum += xLp[j] * y[i+j];
+        }
+
+        xCorr[i] = std::max(-1.0f, sum);
+    }
+
+    bestPitch = this->FindBestPitch(xCorr, y, len >> 1, maxPitch >> 1);
+
+    int offset;
+    /* Refine by pseudo-interpolation. */
+    if ( 0 < bestPitch[0] && bestPitch[0] < ((maxPitch >> 1) - 1)) {
+        float a = xCorr[bestPitch[0] - 1];
+        float b = xCorr[bestPitch[0]];
+        float c = xCorr[bestPitch[0] + 1];
+
+        if ( (c-a) > 0.7*(b-a) ) {
+            offset = 1;
+        } else if ( (a-c) > 0.7*(b-c) ) {
+            offset = -1;
+        } else {
+            offset = 0;
+        }
+    } else {
+        offset = 0;
+    }
+
+    return 2*bestPitch[0] - offset;
+}
+
+arrHp RNNoiseProcess::FindBestPitch(vec1D32F& xCorr, vec1D32F& y, uint32_t len, uint32_t maxPitch)
+{
+    float Syy = 1;
+    arrHp bestNum {-1, -1};
+    arrHp bestDen {0, 0};
+    arrHp bestPitch {0, 1};
+
+    for (size_t j = 0; j < len; ++j) {
+        Syy += (y[j] * y[j]);
+    }
+
+    for (size_t i = 0; i < maxPitch; ++i ) {
+        if (xCorr[i] > 0) {
+            float xCorr16 = xCorr[i] * 1e-12f;  /* Avoid problems when squaring. */
+
+            float num = xCorr16 * xCorr16;
+            if (num*bestDen[1] > bestNum[1]*Syy) {
+                if (num*bestDen[0] > bestNum[0]*Syy) {
+                    bestNum[1] = bestNum[0];
+                    bestDen[1] = bestDen[0];
+                    bestPitch[1] = bestPitch[0];
+                    bestNum[0] = num;
+                    bestDen[0] = Syy;
+                    bestPitch[0] = i;
+                } else {
+                    bestNum[1] = num;
+                    bestDen[1] = Syy;
+                    bestPitch[1] = i;
+                }
+            }
+        }
+
+        Syy += (y[i+len]*y[i+len]) - (y[i]*y[i]);
+        Syy = std::max(1.0f, Syy);
+    }
+
+    return bestPitch;
+}
+
+int RNNoiseProcess::RemoveDoubling(
+    vec1D32F& pitchBuf,
+    uint32_t maxPeriod,
+    uint32_t minPeriod,
+    uint32_t frameSize,
+    size_t pitchIdx0_)
+{
+    constexpr std::array<size_t, 16> secondCheck {0, 0, 3, 2, 3, 2, 5, 2, 3, 2, 3, 2, 5, 2, 3, 2};
+    uint32_t minPeriod0 = minPeriod;
+    float lastPeriod = static_cast<float>(this->m_lastPeriod)/2;
+    float lastGain = static_cast<float>(this->m_lastGain);
+
+    maxPeriod /= 2;
+    minPeriod /= 2;
+    pitchIdx0_ /= 2;
+    frameSize /= 2;
+    uint32_t xStart = maxPeriod;
+
+    if (pitchIdx0_ >= maxPeriod) {
+        pitchIdx0_ = maxPeriod - 1;
+    }
+
+    size_t pitchIdx  = pitchIdx0_;
+    size_t pitchIdx0 = pitchIdx0_;
+
+    float xx = 0;
+    for ( size_t i = xStart; i < xStart+frameSize; ++i) {
+        xx += (pitchBuf[i] * pitchBuf[i]);
+    }
+
+    float xy = 0;
+    for ( size_t i = xStart; i < xStart+frameSize; ++i) {
+        xy += (pitchBuf[i] * pitchBuf[i-pitchIdx0]);
+    }
+
+    vec1D32F yyLookup (maxPeriod+1, 0);
+    yyLookup[0] = xx;
+    float yy = xx;
+
+    for ( size_t i = 1; i < maxPeriod+1; ++i) {
+        yy = yy + (pitchBuf[xStart-i] * pitchBuf[xStart-i]) -
+                (pitchBuf[xStart+frameSize-i] * pitchBuf[xStart+frameSize-i]);
+        yyLookup[i] = std::max(0.0f, yy);
+    }
+
+    yy = yyLookup[pitchIdx0];
+    float bestXy = xy;
+    float bestYy = yy;
+
+    float g = this->ComputePitchGain(xy, xx, yy);
+    float g0 = g;
+
+    /* Look for any pitch at pitchIndex/k. */
+    for ( size_t k = 2; k < 16; ++k) {
+        size_t pitchIdx1 = (2*pitchIdx0+k) / (2*k);
+        if (pitchIdx1 < minPeriod) {
+            break;
+        }
+
+        size_t pitchIdx1b;
+        /* Look for another strong correlation at T1b. */
+        if (k == 2) {
+            if ((pitchIdx1 + pitchIdx0) > maxPeriod) {
+                pitchIdx1b = pitchIdx0;
+            } else {
+                pitchIdx1b = pitchIdx0 + pitchIdx1;
+            }
+        } else {
+            pitchIdx1b = (2*(secondCheck[k])*pitchIdx0 + k) / (2*k);
+        }
+
+        xy = 0;
+        for ( size_t i = xStart; i < xStart+frameSize; ++i) {
+            xy += (pitchBuf[i] * pitchBuf[i-pitchIdx1]);
+        }
+
+        float xy2 = 0;
+        for ( size_t i = xStart; i < xStart+frameSize; ++i) {
+            xy2 += (pitchBuf[i] * pitchBuf[i-pitchIdx1b]);
+        }
+        xy = 0.5f * (xy + xy2);
+        yy = 0.5f * (yyLookup[pitchIdx1] + yyLookup[pitchIdx1b]);
+
+        float g1 = this->ComputePitchGain(xy, xx, yy);
+
+        float cont;
+        if (std::abs(pitchIdx1-lastPeriod) <= 1) {
+            cont = lastGain;
+        } else if (std::abs(pitchIdx1-lastPeriod) <= 2 and 5*k*k < pitchIdx0) {
+            cont = 0.5f*lastGain;
+        } else {
+            cont = 0.0f;
+        }
+
+        float thresh = std::max(0.3, 0.7*g0-cont);
+
+        /* Bias against very high pitch (very short period) to avoid false-positives
+         * due to short-term correlation */
+        if (pitchIdx1 < 3*minPeriod) {
+            thresh = std::max(0.4, 0.85*g0-cont);
+        } else if (pitchIdx1 < 2*minPeriod) {
+            thresh = std::max(0.5, 0.9*g0-cont);
+        }
+        if (g1 > thresh) {
+            bestXy = xy;
+            bestYy = yy;
+            pitchIdx = pitchIdx1;
+            g = g1;
+        }
+    }
+
+    bestXy = std::max(0.0f, bestXy);
+    float pg;
+    if (bestYy <= bestXy) {
+        pg = 1.0;
+    } else {
+        pg = bestXy/(bestYy+1);
+    }
+
+    std::array<float, 3> xCorr {0};
+    for ( size_t k = 0; k < 3; ++k ) {
+        for ( size_t i = xStart; i < xStart+frameSize; ++i) {
+            xCorr[k] += (pitchBuf[i] * pitchBuf[i-(pitchIdx+k-1)]);
+        }
+    }
+
+    size_t offset;
+    if ((xCorr[2]-xCorr[0]) > 0.7*(xCorr[1]-xCorr[0])) {
+        offset = 1;
+    } else if ((xCorr[0]-xCorr[2]) > 0.7*(xCorr[1]-xCorr[2])) {
+        offset = -1;
+    } else {
+        offset = 0;
+    }
+
+    if (pg > g) {
+        pg = g;
+    }
+
+    pitchIdx0_ = 2*pitchIdx + offset;
+
+    if (pitchIdx0_ < minPeriod0) {
+        pitchIdx0_ = minPeriod0;
+    }
+
+    this->m_lastPeriod = pitchIdx0_;
+    this->m_lastGain = pg;
+
+    return this->m_lastPeriod;
+}
+
+float RNNoiseProcess::ComputePitchGain(float xy, float xx, float yy)
+{
+    return xy / math::MathUtils::SqrtF32(1+xx*yy);
+}
+
+void RNNoiseProcess::AutoCorr(
+    const vec1D32F& x,
+    vec1D32F& ac,
+    size_t lag,
+    size_t n)
+{
+    if (n < lag) {
+        printf_err("Invalid parameters for AutoCorr\n");
+        return;
+    }
+
+    auto fastN = n - lag;
+
+    /* Auto-correlation - can be done by PlatformMath functions */
+    this->PitchXCorr(x, x, ac, fastN, lag + 1);
+
+    /* Modify auto-correlation by summing with auto-correlation for different lags. */
+    for (size_t k = 0; k < lag + 1; k++) {
+        float d = 0;
+        for (size_t i = k + fastN; i < n; i++) {
+            d += x[i] * x[i - k];
+        }
+        ac[k] += d;
+    }
+}
+
+
+void RNNoiseProcess::PitchXCorr(
+    const vec1D32F& x,
+    const vec1D32F& y,
+    vec1D32F& ac,
+    size_t len,
+    size_t maxPitch)
+{
+    for (size_t i = 0; i < maxPitch; i++) {
+        float sum = 0;
+        for (size_t j = 0; j < len; j++) {
+            sum += x[j] * y[i + j];
+        }
+        ac[i] = sum;
+    }
+}
+
+/* Linear predictor coefficients */
+void RNNoiseProcess::LPC(
+    const vec1D32F& ac,
+    int32_t p,
+    vec1D32F& lpc)
+{
+    auto error = ac[0];
+
+    if (error != 0) {
+        for (int i = 0; i < p; i++) {
+
+            /* Sum up this iteration's reflection coefficient */
+            float rr = 0;
+            for (int j = 0; j < i; j++) {
+                rr += lpc[j] * ac[i - j];
+            }
+
+            rr += ac[i + 1];
+            auto r = -rr / error;
+
+            /* Update LP coefficients and total error */
+            lpc[i] = r;
+            for (int j = 0; j < ((i + 1) >> 1); j++) {
+                auto tmp1 = lpc[j];
+                auto tmp2 = lpc[i - 1 - j];
+                lpc[j] = tmp1 + (r * tmp2);
+                lpc[i - 1 - j] = tmp2 + (r * tmp1);
+            }
+
+            error = error - (r * r * error);
+
+            /* Bail out once we get 30dB gain */
+            if (error < (0.001 * ac[0])) {
+                break;
+            }
+        }
+    }
+}
+
+void RNNoiseProcess::Fir5(
+    const vec1D32F &num,
+    uint32_t N,
+    vec1D32F &x)
+{
+    auto num0 = num[0];
+    auto num1 = num[1];
+    auto num2 = num[2];
+    auto num3 = num[3];
+    auto num4 = num[4];
+    auto mem0 = 0;
+    auto mem1 = 0;
+    auto mem2 = 0;
+    auto mem3 = 0;
+    auto mem4 = 0;
+    for (uint32_t i = 0; i < N; i++)
+    {
+        auto sum_ = x[i] +  (num0 * mem0) + (num1 * mem1) +
+                    (num2 * mem2) + (num3 * mem3) + (num4 * mem4);
+        mem4 = mem3;
+        mem3 = mem2;
+        mem2 = mem1;
+        mem1 = mem0;
+        mem0 = x[i];
+        x[i] = sum_;
+    }
+}
+
+void RNNoiseProcess::PitchFilter(FrameFeatures &features, vec1D32F &g) {
+    std::vector<float> r(NB_BANDS, 0);
+    std::vector<float> rf(FREQ_SIZE, 0);
+    std::vector<float> newE(NB_BANDS);
+
+    for (size_t i = 0; i < NB_BANDS; i++) {
+        if (features.m_Exp[i] > g[i]) {
+            r[i] = 1;
+        } else {
+
+
+            r[i] = std::pow(features.m_Exp[i], 2) * (1 - std::pow(g[i], 2)) /
+                   (.001 + std::pow(g[i], 2) * (1 - std::pow(features.m_Exp[i], 2)));
+        }
+
+
+        r[i] = math::MathUtils::SqrtF32(std::min(1.0f, std::max(0.0f, r[i])));
+        r[i] *= math::MathUtils::SqrtF32(features.m_Ex[i] / (1e-8f + features.m_Ep[i]));
+    }
+
+    InterpBandGain(rf, r);
+    for (size_t i = 0; i < FREQ_SIZE - 1; i++) {
+        features.m_fftX[2 * i] += rf[i] * features.m_fftP[2 * i];  /* Real. */
+        features.m_fftX[2 * i + 1] += rf[i] * features.m_fftP[2 * i + 1];  /* Imaginary. */
+
+    }
+    ComputeBandEnergy(features.m_fftX, newE);
+    std::vector<float> norm(NB_BANDS);
+    std::vector<float> normf(FRAME_SIZE, 0);
+    for (size_t i = 0; i < NB_BANDS; i++) {
+        norm[i] = math::MathUtils::SqrtF32(features.m_Ex[i] / (1e-8f + newE[i]));
+    }
+
+    InterpBandGain(normf, norm);
+    for (size_t i = 0; i < FREQ_SIZE - 1; i++) {
+        features.m_fftX[2 * i] *= normf[i];  /* Real. */
+        features.m_fftX[2 * i + 1] *= normf[i];  /* Imaginary. */
+
+    }
+}
+
+void RNNoiseProcess::FrameSynthesis(vec1D32F& outFrame, vec1D32F& fftY) {
+    std::vector<float> x(WINDOW_SIZE, 0);
+    InverseTransform(x, fftY);
+    ApplyWindow(x);
+    for (size_t i = 0; i < FRAME_SIZE; i++) {
+        outFrame[i] = x[i] + m_synthesisMem[i];
+    }
+    memcpy((m_synthesisMem.data()), &x[FRAME_SIZE], FRAME_SIZE*sizeof(float));
+}
+
+void RNNoiseProcess::InterpBandGain(vec1D32F& g, vec1D32F& bandE) {
+    for (size_t i = 0; i < NB_BANDS - 1; i++) {
+        int bandSize = (m_eband5ms[i + 1] - m_eband5ms[i]) << FRAME_SIZE_SHIFT;
+        for (int j = 0; j < bandSize; j++) {
+            float frac = static_cast<float>(j) / bandSize;
+            g[(m_eband5ms[i] << FRAME_SIZE_SHIFT) + j] = (1 - frac) * bandE[i] + frac * bandE[i + 1];
+        }
+    }
+}
+
+void RNNoiseProcess::InverseTransform(vec1D32F& out, vec1D32F& fftXIn) {
+
+    std::vector<float> x(WINDOW_SIZE * 2);  /* This is complex. */
+    vec1D32F newFFT;  /* This is complex. */
+
+    size_t i;
+    for (i = 0; i < FREQ_SIZE * 2; i++) {
+        x[i] = fftXIn[i];
+    }
+    for (i = FREQ_SIZE; i < WINDOW_SIZE; i++) {
+        x[2 * i] = x[2 * (WINDOW_SIZE - i)];  /* Real. */
+        x[2 * i + 1] = -x[2 * (WINDOW_SIZE - i) + 1];  /* Imaginary. */
+    }
+
+    constexpr uint32_t numFFt = 2 * FRAME_SIZE;
+    static_assert(numFFt != 0);
+
+    vec1D32F fftOut = vec1D32F(x.size(), 0);
+    math::MathUtils::FftF32(x,fftOut, m_fftInstCmplx);
+
+    /* Normalize. */
+    for (auto &f: fftOut) {
+        f /= numFFt;
+    }
+
+    out[0] = WINDOW_SIZE * fftOut[0];  /* Real. */
+    for (i = 1; i < WINDOW_SIZE; i++) {
+        out[i] = WINDOW_SIZE * fftOut[(WINDOW_SIZE * 2) - (2 * i)];  /* Real. */
+    }
+}
+
+
+} /* namespace rnn */
+} /* namespace app */
+} /* namspace arm */