From f469b63d44bc8ccbf18873a153f277e507731249 Mon Sep 17 00:00:00 2001
From: Gustaf Ullberg <gustaf@webrtc.org>
Date: Thu, 7 Jun 2018 11:25:21 +0200
Subject: [PATCH] AEC3: Improved anti-aliasing filter for DSF 4
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This change contains a new anti-aliasing filter for the delay estimator
for down-sampling factor 4. The new (elliptic) filter has a much wider
main lobe allowing for faster convergence.

Bug: webrtc:9288,chromium:846615
Change-Id: Id109974a59fe6f48c5e0ccc4f4e06c0d94c8bd03
Reviewed-on: https://webrtc-review.googlesource.com/81680
Reviewed-by: Per Åhgren <peah@webrtc.org>
Commit-Queue: Gustaf Ullberg <gustaf@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23534}
---
 modules/audio_processing/aec3/decimator.cc         |  8 ++++----
 .../aec3/echo_path_delay_estimator_unittest.cc     | 14 ++++++++------
 2 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/modules/audio_processing/aec3/decimator.cc b/modules/audio_processing/aec3/decimator.cc
index 0ebc7db0bb..3f350582b4 100644
--- a/modules/audio_processing/aec3/decimator.cc
+++ b/modules/audio_processing/aec3/decimator.cc
@@ -20,11 +20,11 @@ const std::vector<CascadedBiQuadFilter::BiQuadParam> kLowPassFilterDS2 = {
     {{-1.f, 0.f}, {0.13833231f, 0.40743176f}, 0.22711796393486466f},
     {{-1.f, 0.f}, {0.13833231f, 0.40743176f}, 0.22711796393486466f}};
 
-// signal.butter(2, 750/8000.0, 'lowpass', analog=False)
+// signal.ellip(6, 1, 40, 1800/8000, btype='lowpass', analog=False)
 const std::vector<CascadedBiQuadFilter::BiQuadParam> kLowPassFilterDS4 = {
-    {{-1.f, 0.f}, {0.79396855f, 0.17030506f}, 0.017863192751682862f},
-    {{-1.f, 0.f}, {0.79396855f, 0.17030506f}, 0.017863192751682862f},
-    {{-1.f, 0.f}, {0.79396855f, 0.17030506f}, 0.017863192751682862f}};
+    {{-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> kBandPassFilterDS8 = {
diff --git a/modules/audio_processing/aec3/echo_path_delay_estimator_unittest.cc b/modules/audio_processing/aec3/echo_path_delay_estimator_unittest.cc
index 38f31c9ea6..8dd3bc638b 100644
--- a/modules/audio_processing/aec3/echo_path_delay_estimator_unittest.cc
+++ b/modules/audio_processing/aec3/echo_path_delay_estimator_unittest.cc
@@ -93,12 +93,14 @@ TEST(EchoPathDelayEstimator, DelayEstimation) {
       }
 
       if (estimated_delay_samples) {
-        // Due to the internal down-sampling done inside the delay estimator
-        // the estimated delay cannot be expected to be exact to the true delay.
-        EXPECT_NEAR(delay_samples,
-                    estimated_delay_samples->delay -
-                        (config.delay.api_call_jitter_blocks + 1) * 64,
-                    config.delay.down_sampling_factor);
+        // Allow estimated delay to be off by one sample in the down-sampled
+        // domain.
+        size_t delay_ds = delay_samples / down_sampling_factor;
+        size_t estimated_delay_ds =
+            (estimated_delay_samples->delay -
+             (config.delay.api_call_jitter_blocks + 1) * 64) /
+            down_sampling_factor;
+        EXPECT_NEAR(delay_ds, estimated_delay_ds, 1);
       } else {
         ADD_FAILURE();
       }