1 files changed, 90 insertions, 0 deletions
diff --git a/source/use_case/ad/src/AdMelSpectrogram.cc b/source/use_case/ad/src/AdMelSpectrogram.cc
new file mode 100644
index 0000000..183c05c
--- /dev/null
+++ b/source/use_case/ad/src/AdMelSpectrogram.cc
@@ -0,0 +1,90 @@
+/*
+ * 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 "AdMelSpectrogram.hpp"
+
+#include "PlatformMath.hpp"
+
+namespace arm {
+namespace app {
+namespace audio {
+
+    bool AdMelSpectrogram::ApplyMelFilterBank(
+            std::vector<float>&                 fftVec,
+            std::vector<std::vector<float>>&    melFilterBank,
+            std::vector<int32_t>&               filterBankFilterFirst,
+            std::vector<int32_t>&               filterBankFilterLast,
+            std::vector<float>&                 melEnergies)
+    {
+        const size_t numBanks = melEnergies.size();
+
+        if (numBanks != filterBankFilterFirst.size() ||
+            numBanks != filterBankFilterLast.size()) {
+            printf_err("unexpected filter bank lengths\n");
+            return false;
+        }
+
+        for (size_t bin = 0; bin < numBanks; ++bin) {
+            auto filterBankIter = melFilterBank[bin].begin();
+            float melEnergy = 1e-10; /* Avoid log of zero at later stages. */
+            const int32_t firstIndex = filterBankFilterFirst[bin];
+            const int32_t lastIndex = filterBankFilterLast[bin];
+
+            for (int32_t i = firstIndex; i <= lastIndex; ++i) {
+                melEnergy += (*filterBankIter++ * fftVec[i]);
+            }
+
+            melEnergies[bin] = melEnergy;
+        }
+
+        return true;
+    }
+
+    void AdMelSpectrogram::ConvertToLogarithmicScale(
+            std::vector<float>& melEnergies)
+    {
+        /* Container for natural logarithms of mel energies */
+        std::vector <float> vecLogEnergies(melEnergies.size(), 0.f);
+
+        /* Because we are taking natural logs, we need to multiply by log10(e).
+         * Also, for wav2letter model, we scale our log10 values by 10 */
+        constexpr float multiplier = 10.0 * /* default scalar */
+                                     0.4342944819032518; /* log10f(std::exp(1.0))*/
+
+        /* Take log of the whole vector */
+        math::MathUtils::VecLogarithmF32(melEnergies, vecLogEnergies);
+
+        /* Scale the log values. */
+        for (auto iterM = melEnergies.begin(), iterL = vecLogEnergies.begin();
+             iterM != melEnergies.end(); ++iterM, ++iterL) {
+
+            *iterM = *iterL * multiplier;
+        }
+    }
+
+    float AdMelSpectrogram::GetMelFilterBankNormaliser(
+            const float&    leftMel,
+            const float&    rightMel,
+            const bool      useHTKMethod)
+    {
+        /* Slaney normalization for mel weights. */
+        return (2.0f / (AdMelSpectrogram::InverseMelScale(rightMel, useHTKMethod) -
+                        AdMelSpectrogram::InverseMelScale(leftMel, useHTKMethod)));
+    }
+
+} /* namespace audio */
+} /* namespace app */
+} /* namespace arm */