AGC2 VAD probability: instant decay / slow attack

Feature added to gain robustness to occasional VAD speech probability
spikes. In such a case, the attack process reduces the chance that the
smoothed values are greater than the speech threshold.

Bug: webrtc:7494
Change-Id: I6babe5afe30ea3dea021181a19d86bb74b33a98c
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/185046
Commit-Queue: Alessio Bazzica <alessiob@webrtc.org>
Reviewed-by: Gustaf Ullberg <gustaf@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#32198}

modules/audio_processing/agc2/BUILD.gn

@@ -95,6 +95,7 @@ rtc_library("common") {
     "../../../rtc_base:rtc_base_approved",
     "../../../system_wrappers:field_trial",
   ]
+  absl_deps = [ "//third_party/abseil-cpp/absl/types:optional" ]
 }
 
 rtc_library("fixed_digital") {
@@ -168,6 +169,7 @@ rtc_library("rnn_vad_with_level") {
     "vad_with_level.h",
   ]
   deps = [
+    ":common",
     "..:audio_frame_view",
     "../../../api:array_view",
     "../../../common_audio",
@@ -265,9 +267,12 @@ rtc_library("rnn_vad_with_level_unittests") {
   testonly = true
   sources = [ "vad_with_level_unittest.cc" ]
   deps = [
+    ":common",
     ":rnn_vad_with_level",
     "..:audio_frame_view",
     "../../../rtc_base:gunit_helpers",
+    "../../../rtc_base:safe_compare",
+    "../../../test:test_support",
   ]
 }
 

modules/audio_processing/agc2/agc2_common.h

@@ -49,6 +49,9 @@ constexpr float kFullBufferLeakFactor = 1.f - 1.f / kFullBufferSizeMs;
 
 constexpr float kInitialSpeechLevelEstimateDbfs = -30.f;
 
+// Robust VAD probability and speech decisions.
+constexpr float kDefaultSmoothedVadProbabilityAttack = 1.f;
+
 // Saturation Protector settings.
 float GetInitialSaturationMarginDb();
 float GetExtraSaturationMarginOffsetDb();

modules/audio_processing/agc2/vad_with_level.cc

@@ -17,6 +17,7 @@
 #include "api/array_view.h"
 #include "common_audio/include/audio_util.h"
 #include "common_audio/resampler/include/push_resampler.h"
+#include "modules/audio_processing/agc2/agc2_common.h"
 #include "modules/audio_processing/agc2/rnn_vad/common.h"
 #include "modules/audio_processing/agc2/rnn_vad/features_extraction.h"
 #include "modules/audio_processing/agc2/rnn_vad/rnn.h"
@@ -61,12 +62,32 @@ class Vad : public VoiceActivityDetector {
   rnn_vad::RnnBasedVad rnn_vad_;
 };
 
+// Returns an updated version of `p_old` by using instant decay and the given
+// `attack` on a new VAD probability value `p_new`.
+float SmoothedVadProbability(float p_old, float p_new, float attack) {
+  RTC_DCHECK_GT(attack, 0.f);
+  RTC_DCHECK_LE(attack, 1.f);
+  if (p_new < p_old || attack == 1.f) {
+    // Instant decay (or no smoothing).
+    return p_new;
+  } else {
+    // Attack phase.
+    return attack * p_new + (1.f - attack) * p_old;
+  }
+}
+
 }  // namespace
 
-VadLevelAnalyzer::VadLevelAnalyzer() : vad_(std::make_unique<Vad>()) {}
+VadLevelAnalyzer::VadLevelAnalyzer()
+    : VadLevelAnalyzer(kDefaultSmoothedVadProbabilityAttack,
+                       std::make_unique<Vad>()) {}
 
-VadLevelAnalyzer::VadLevelAnalyzer(std::unique_ptr<VoiceActivityDetector> vad)
-    : vad_(std::move(vad)) {
+VadLevelAnalyzer::VadLevelAnalyzer(float vad_probability_attack)
+    : VadLevelAnalyzer(vad_probability_attack, std::make_unique<Vad>()) {}
+
+VadLevelAnalyzer::VadLevelAnalyzer(float vad_probability_attack,
+                                   std::unique_ptr<VoiceActivityDetector> vad)
+    : vad_(std::move(vad)), vad_probability_attack_(vad_probability_attack) {
   RTC_DCHECK(vad_);
 }
 
@@ -74,13 +95,18 @@ VadLevelAnalyzer::~VadLevelAnalyzer() = default;
 
 VadLevelAnalyzer::Result VadLevelAnalyzer::AnalyzeFrame(
     AudioFrameView<const float> frame) {
+  // Compute levels.
   float peak = 0.f;
   float rms = 0.f;
   for (const auto& x : frame.channel(0)) {
     peak = std::max(std::fabs(x), peak);
     rms += x * x;
   }
-  return {vad_->ComputeProbability(frame),
+  // Compute smoothed speech probability.
+  vad_probability_ = SmoothedVadProbability(
+      /*p_old=*/vad_probability_, /*p_new=*/vad_->ComputeProbability(frame),
+      vad_probability_attack_);
+  return {vad_probability_,
           FloatS16ToDbfs(std::sqrt(rms / frame.samples_per_channel())),
           FloatS16ToDbfs(peak)};
 }

modules/audio_processing/agc2/vad_with_level.h

@@ -36,8 +36,10 @@ class VadLevelAnalyzer {
 
   // Ctor. Uses the default VAD.
   VadLevelAnalyzer();
+  explicit VadLevelAnalyzer(float vad_probability_attack);
   // Ctor. Uses a custom `vad`.
-  explicit VadLevelAnalyzer(std::unique_ptr<VoiceActivityDetector> vad);
+  VadLevelAnalyzer(float vad_probability_attack,
+                   std::unique_ptr<VoiceActivityDetector> vad);
   VadLevelAnalyzer(const VadLevelAnalyzer&) = delete;
   VadLevelAnalyzer& operator=(const VadLevelAnalyzer&) = delete;
   ~VadLevelAnalyzer();
@@ -47,6 +49,8 @@ class VadLevelAnalyzer {
 
  private:
   std::unique_ptr<VoiceActivityDetector> vad_;
+  const float vad_probability_attack_;
+  float vad_probability_ = 0.f;
 };
 
 }  // namespace webrtc

modules/audio_processing/agc2/vad_with_level_unittest.cc

@@ -10,30 +10,121 @@
 
 #include "modules/audio_processing/agc2/vad_with_level.h"
 
+#include <memory>
+#include <vector>
+
+#include "modules/audio_processing/agc2/agc2_common.h"
+#include "modules/audio_processing/include/audio_frame_view.h"
 #include "rtc_base/gunit.h"
+#include "rtc_base/numerics/safe_compare.h"
+#include "test/gmock.h"
 
 namespace webrtc {
 namespace {
 
-TEST(AutomaticGainController2VadWithLevelEstimator,
-     PeakLevelGreaterThanRmsLevel) {
-  constexpr size_t kSampleRateHz = 8000;
+using ::testing::AnyNumber;
+using ::testing::ReturnRoundRobin;
 
-  // 10 ms input frame, constant except for one peak value.
-  // Handcrafted so that the average is lower than the peak value.
-  std::array<float, kSampleRateHz / 100> frame;
-  frame.fill(1000.f);
-  frame[10] = 2000.f;
-  float* const channel0 = frame.data();
-  AudioFrameView<float> frame_view(&channel0, 1, frame.size());
+constexpr float kInstantAttack = 1.f;
+constexpr float kSlowAttack = 0.1f;
+
+constexpr int kSampleRateHz = 8000;
+
+class MockVad : public VadLevelAnalyzer::VoiceActivityDetector {
+ public:
+  MOCK_METHOD(float,
+              ComputeProbability,
+              (AudioFrameView<const float> frame),
+              (override));
+};
+
+// Creates a `VadLevelAnalyzer` injecting a mock VAD which repeatedly returns
+// the next value from `speech_probabilities` until it reaches the end and will
+// restart from the beginning.
+std::unique_ptr<VadLevelAnalyzer> CreateVadLevelAnalyzerWithMockVad(
+    float vad_probability_attack,
+    const std::vector<float>& speech_probabilities) {
+  auto vad = std::make_unique<MockVad>();
+  EXPECT_CALL(*vad, ComputeProbability)
+      .Times(AnyNumber())
+      .WillRepeatedly(ReturnRoundRobin(speech_probabilities));
+  return std::make_unique<VadLevelAnalyzer>(vad_probability_attack,
+                                            std::move(vad));
+}
+
+// 10 ms mono frame.
+struct FrameWithView {
+  // Ctor. Initializes the frame samples with `value`.
+  FrameWithView(float value = 0.f)
+      : channel0(samples.data()),
+        view(&channel0, /*num_channels=*/1, samples.size()) {
+    samples.fill(value);
+  }
+  std::array<float, kSampleRateHz / 100> samples;
+  const float* const channel0;
+  const AudioFrameView<const float> view;
+};
+
+TEST(AutomaticGainController2VadLevelAnalyzer, PeakLevelGreaterThanRmsLevel) {
+  // Handcrafted frame so that the average is lower than the peak value.
+  FrameWithView frame(1000.f);  // Constant frame.
+  frame.samples[10] = 2000.f;   // Except for one peak value.
 
   // Compute audio frame levels (the VAD result is ignored).
   VadLevelAnalyzer analyzer;
-  auto levels_and_vad_prob = analyzer.AnalyzeFrame(frame_view);
+  auto levels_and_vad_prob = analyzer.AnalyzeFrame(frame.view);
 
   // Compare peak and RMS levels.
   EXPECT_LT(levels_and_vad_prob.rms_dbfs, levels_and_vad_prob.peak_dbfs);
 }
 
+// Checks that the unprocessed and the smoothed speech probabilities match when
+// instant attack is used.
+TEST(AutomaticGainController2VadLevelAnalyzer, NoSpeechProbabilitySmoothing) {
+  const std::vector<float> speech_probabilities{0.709f, 0.484f, 0.882f, 0.167f,
+                                                0.44f,  0.525f, 0.858f, 0.314f,
+                                                0.653f, 0.965f, 0.413f, 0.f};
+  auto analyzer =
+      CreateVadLevelAnalyzerWithMockVad(kInstantAttack, speech_probabilities);
+  FrameWithView frame;
+  for (int i = 0; rtc::SafeLt(i, speech_probabilities.size()); ++i) {
+    SCOPED_TRACE(i);
+    EXPECT_EQ(speech_probabilities[i],
+              analyzer->AnalyzeFrame(frame.view).speech_probability);
+  }
+}
+
+// Checks that the smoothed speech probability does not instantly converge to
+// the unprocessed one when slow attack is used.
+TEST(AutomaticGainController2VadLevelAnalyzer,
+     SlowAttackSpeechProbabilitySmoothing) {
+  const std::vector<float> speech_probabilities{0.f, 0.f, 1.f, 1.f, 1.f, 1.f};
+  auto analyzer =
+      CreateVadLevelAnalyzerWithMockVad(kSlowAttack, speech_probabilities);
+  FrameWithView frame;
+  float prev_probability = 0.f;
+  for (int i = 0; rtc::SafeLt(i, speech_probabilities.size()); ++i) {
+    SCOPED_TRACE(i);
+    const float smoothed_probability =
+        analyzer->AnalyzeFrame(frame.view).speech_probability;
+    EXPECT_LT(smoothed_probability, 1.f);  // Not enough time to reach 1.
+    EXPECT_LE(prev_probability, smoothed_probability);  // Converge towards 1.
+    prev_probability = smoothed_probability;
+  }
+}
+
+// Checks that the smoothed speech probability instantly decays to the
+// unprocessed one when slow attack is used.
+TEST(AutomaticGainController2VadLevelAnalyzer, SpeechProbabilityInstantDecay) {
+  const std::vector<float> speech_probabilities{1.f, 1.f, 1.f, 1.f, 1.f, 0.f};
+  auto analyzer =
+      CreateVadLevelAnalyzerWithMockVad(kSlowAttack, speech_probabilities);
+  FrameWithView frame;
+  for (int i = 0; rtc::SafeLt(i, speech_probabilities.size() - 1); ++i) {
+    analyzer->AnalyzeFrame(frame.view);
+  }
+  EXPECT_EQ(0.f, analyzer->AnalyzeFrame(frame.view).speech_probability);
+}
+
 }  // namespace
 }  // namespace webrtc