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Diffstat (limited to 'third_party/libwebrtc/modules/audio_processing/agc2/rnn_vad/lp_residual.cc')
-rw-r--r-- | third_party/libwebrtc/modules/audio_processing/agc2/rnn_vad/lp_residual.cc | 141 |
1 files changed, 141 insertions, 0 deletions
diff --git a/third_party/libwebrtc/modules/audio_processing/agc2/rnn_vad/lp_residual.cc b/third_party/libwebrtc/modules/audio_processing/agc2/rnn_vad/lp_residual.cc new file mode 100644 index 0000000000..484bfba459 --- /dev/null +++ b/third_party/libwebrtc/modules/audio_processing/agc2/rnn_vad/lp_residual.cc @@ -0,0 +1,141 @@ +/* + * Copyright (c) 2018 The WebRTC project authors. All Rights Reserved. + * + * Use of this source code is governed by a BSD-style license + * that can be found in the LICENSE file in the root of the source + * tree. An additional intellectual property rights grant can be found + * in the file PATENTS. All contributing project authors may + * be found in the AUTHORS file in the root of the source tree. + */ + +#include "modules/audio_processing/agc2/rnn_vad/lp_residual.h" + +#include <algorithm> +#include <array> +#include <cmath> +#include <numeric> + +#include "rtc_base/checks.h" +#include "rtc_base/numerics/safe_compare.h" + +namespace webrtc { +namespace rnn_vad { +namespace { + +// Computes auto-correlation coefficients for `x` and writes them in +// `auto_corr`. The lag values are in {0, ..., max_lag - 1}, where max_lag +// equals the size of `auto_corr`. +void ComputeAutoCorrelation( + rtc::ArrayView<const float> x, + rtc::ArrayView<float, kNumLpcCoefficients> auto_corr) { + constexpr int max_lag = auto_corr.size(); + RTC_DCHECK_LT(max_lag, x.size()); + for (int lag = 0; lag < max_lag; ++lag) { + auto_corr[lag] = + std::inner_product(x.begin(), x.end() - lag, x.begin() + lag, 0.f); + } +} + +// Applies denoising to the auto-correlation coefficients. +void DenoiseAutoCorrelation( + rtc::ArrayView<float, kNumLpcCoefficients> auto_corr) { + // Assume -40 dB white noise floor. + auto_corr[0] *= 1.0001f; + // Hard-coded values obtained as + // [np.float32((0.008*0.008*i*i)) for i in range(1,5)]. + auto_corr[1] -= auto_corr[1] * 0.000064f; + auto_corr[2] -= auto_corr[2] * 0.000256f; + auto_corr[3] -= auto_corr[3] * 0.000576f; + auto_corr[4] -= auto_corr[4] * 0.001024f; + static_assert(kNumLpcCoefficients == 5, "Update `auto_corr`."); +} + +// Computes the initial inverse filter coefficients given the auto-correlation +// coefficients of an input frame. +void ComputeInitialInverseFilterCoefficients( + rtc::ArrayView<const float, kNumLpcCoefficients> auto_corr, + rtc::ArrayView<float, kNumLpcCoefficients - 1> lpc_coeffs) { + float error = auto_corr[0]; + for (int i = 0; i < kNumLpcCoefficients - 1; ++i) { + float reflection_coeff = 0.f; + for (int j = 0; j < i; ++j) { + reflection_coeff += lpc_coeffs[j] * auto_corr[i - j]; + } + reflection_coeff += auto_corr[i + 1]; + + // Avoid division by numbers close to zero. + constexpr float kMinErrorMagnitude = 1e-6f; + if (std::fabs(error) < kMinErrorMagnitude) { + error = std::copysign(kMinErrorMagnitude, error); + } + + reflection_coeff /= -error; + // Update LPC coefficients and total error. + lpc_coeffs[i] = reflection_coeff; + for (int j = 0; j < ((i + 1) >> 1); ++j) { + const float tmp1 = lpc_coeffs[j]; + const float tmp2 = lpc_coeffs[i - 1 - j]; + lpc_coeffs[j] = tmp1 + reflection_coeff * tmp2; + lpc_coeffs[i - 1 - j] = tmp2 + reflection_coeff * tmp1; + } + error -= reflection_coeff * reflection_coeff * error; + if (error < 0.001f * auto_corr[0]) { + break; + } + } +} + +} // namespace + +void ComputeAndPostProcessLpcCoefficients( + rtc::ArrayView<const float> x, + rtc::ArrayView<float, kNumLpcCoefficients> lpc_coeffs) { + std::array<float, kNumLpcCoefficients> auto_corr; + ComputeAutoCorrelation(x, auto_corr); + if (auto_corr[0] == 0.f) { // Empty frame. + std::fill(lpc_coeffs.begin(), lpc_coeffs.end(), 0); + return; + } + DenoiseAutoCorrelation(auto_corr); + std::array<float, kNumLpcCoefficients - 1> lpc_coeffs_pre{}; + ComputeInitialInverseFilterCoefficients(auto_corr, lpc_coeffs_pre); + // LPC coefficients post-processing. + // TODO(bugs.webrtc.org/9076): Consider removing these steps. + lpc_coeffs_pre[0] *= 0.9f; + lpc_coeffs_pre[1] *= 0.9f * 0.9f; + lpc_coeffs_pre[2] *= 0.9f * 0.9f * 0.9f; + lpc_coeffs_pre[3] *= 0.9f * 0.9f * 0.9f * 0.9f; + constexpr float kC = 0.8f; + lpc_coeffs[0] = lpc_coeffs_pre[0] + kC; + lpc_coeffs[1] = lpc_coeffs_pre[1] + kC * lpc_coeffs_pre[0]; + lpc_coeffs[2] = lpc_coeffs_pre[2] + kC * lpc_coeffs_pre[1]; + lpc_coeffs[3] = lpc_coeffs_pre[3] + kC * lpc_coeffs_pre[2]; + lpc_coeffs[4] = kC * lpc_coeffs_pre[3]; + static_assert(kNumLpcCoefficients == 5, "Update `lpc_coeffs(_pre)`."); +} + +void ComputeLpResidual( + rtc::ArrayView<const float, kNumLpcCoefficients> lpc_coeffs, + rtc::ArrayView<const float> x, + rtc::ArrayView<float> y) { + RTC_DCHECK_GT(x.size(), kNumLpcCoefficients); + RTC_DCHECK_EQ(x.size(), y.size()); + // The code below implements the following operation: + // y[i] = x[i] + dot_product({x[i], ..., x[i - kNumLpcCoefficients + 1]}, + // lpc_coeffs) + // Edge case: i < kNumLpcCoefficients. + y[0] = x[0]; + for (int i = 1; i < kNumLpcCoefficients; ++i) { + y[i] = + std::inner_product(x.crend() - i, x.crend(), lpc_coeffs.cbegin(), x[i]); + } + // Regular case. + auto last = x.crend(); + for (int i = kNumLpcCoefficients; rtc::SafeLt(i, y.size()); ++i, --last) { + y[i] = std::inner_product(last - kNumLpcCoefficients, last, + lpc_coeffs.cbegin(), x[i]); + } +} + +} // namespace rnn_vad +} // namespace webrtc |