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diff --git a/webrtc/modules/audio_processing/aec3/decimator.cc b/webrtc/modules/audio_processing/aec3/decimator.cc
new file mode 100644
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+++ b/webrtc/modules/audio_processing/aec3/decimator.cc
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+/*
+ *  Copyright (c) 2017 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/aec3/decimator.h"
+
+#include <array>
+#include <vector>
+
+#include "modules/audio_processing/aec3/aec3_common.h"
+#include "rtc_base/checks.h"
+
+namespace webrtc {
+namespace {
+
+// signal.butter(2, 3400/8000.0, 'lowpass', analog=False)
+const std::vector<CascadedBiQuadFilter::BiQuadParam> GetLowPassFilterDS2() {
+  return std::vector<CascadedBiQuadFilter::BiQuadParam>{
+      {{-1.f, 0.f}, {0.13833231f, 0.40743176f}, 0.22711796393486466f},
+      {{-1.f, 0.f}, {0.13833231f, 0.40743176f}, 0.22711796393486466f},
+      {{-1.f, 0.f}, {0.13833231f, 0.40743176f}, 0.22711796393486466f}};
+}
+
+// signal.ellip(6, 1, 40, 1800/8000, btype='lowpass', analog=False)
+const std::vector<CascadedBiQuadFilter::BiQuadParam> GetLowPassFilterDS4() {
+  return std::vector<CascadedBiQuadFilter::BiQuadParam>{
+      {{-0.08873842f, 0.99605496f}, {0.75916227f, 0.23841065f}, 0.26250696827f},
+      {{0.62273832f, 0.78243018f}, {0.74892112f, 0.5410152f}, 0.26250696827f},
+      {{0.71107693f, 0.70311421f}, {0.74895534f, 0.63924616f}, 0.26250696827f}};
+}
+
+// signal.cheby1(1, 6, [1000/8000, 2000/8000], btype='bandpass', analog=False)
+const std::vector<CascadedBiQuadFilter::BiQuadParam> GetBandPassFilterDS8() {
+  return std::vector<CascadedBiQuadFilter::BiQuadParam>{
+      {{1.f, 0.f}, {0.7601815f, 0.46423542f}, 0.10330478266505948f, true},
+      {{1.f, 0.f}, {0.7601815f, 0.46423542f}, 0.10330478266505948f, true},
+      {{1.f, 0.f}, {0.7601815f, 0.46423542f}, 0.10330478266505948f, true},
+      {{1.f, 0.f}, {0.7601815f, 0.46423542f}, 0.10330478266505948f, true},
+      {{1.f, 0.f}, {0.7601815f, 0.46423542f}, 0.10330478266505948f, true}};
+}
+
+// signal.butter(2, 1000/8000.0, 'highpass', analog=False)
+const std::vector<CascadedBiQuadFilter::BiQuadParam> GetHighPassFilter() {
+  return std::vector<CascadedBiQuadFilter::BiQuadParam>{
+      {{1.f, 0.f}, {0.72712179f, 0.21296904f}, 0.7570763753338849f}};
+}
+
+const std::vector<CascadedBiQuadFilter::BiQuadParam> GetPassThroughFilter() {
+  return std::vector<CascadedBiQuadFilter::BiQuadParam>{};
+}
+}  // namespace
+
+Decimator::Decimator(size_t down_sampling_factor)
+    : down_sampling_factor_(down_sampling_factor),
+      anti_aliasing_filter_(down_sampling_factor_ == 4
+                                ? GetLowPassFilterDS4()
+                                : (down_sampling_factor_ == 8
+                                       ? GetBandPassFilterDS8()
+                                       : GetLowPassFilterDS2())),
+      noise_reduction_filter_(down_sampling_factor_ == 8
+                                  ? GetPassThroughFilter()
+                                  : GetHighPassFilter()) {
+  RTC_DCHECK(down_sampling_factor_ == 2 || down_sampling_factor_ == 4 ||
+             down_sampling_factor_ == 8);
+}
+
+void Decimator::Decimate(rtc::ArrayView<const float> in,
+                         rtc::ArrayView<float> out) {
+  RTC_DCHECK_EQ(kBlockSize, in.size());
+  RTC_DCHECK_EQ(kBlockSize / down_sampling_factor_, out.size());
+  std::array<float, kBlockSize> x;
+
+  // Limit the frequency content of the signal to avoid aliasing.
+  anti_aliasing_filter_.Process(in, x);
+
+  // Reduce the impact of near-end noise.
+  noise_reduction_filter_.Process(x);
+
+  // Downsample the signal.
+  for (size_t j = 0, k = 0; j < out.size(); ++j, k += down_sampling_factor_) {
+    RTC_DCHECK_GT(kBlockSize, k);
+    out[j] = x[k];
+  }
+}
+
+}  // namespace webrtc