Make governed volume linearly increasing.

Change-Id: I1d6967b592fbdbaa682ba85c572e4a6d0576eeec
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1937585
Commit-Queue: Michael Montvelishsky <mont@chromium.org>
Auto-Submit: Michael Montvelishsky <mont@chromium.org>
Reviewed-by: Kenneth MacKay <kmackay@chromium.org>
Cr-Commit-Position: refs/heads/master@{#719491}

chromecast/media/cma/backend/mixer/post_processors/governor.cc

@@ -21,6 +21,7 @@ namespace {
 
 const int kNoVolume = -1;
 const float kEpsilon = std::numeric_limits<float>::epsilon();
+const float kMaxOnSetVolume = 0.989;  // -0.1dB
 
 // Configuration strings:
 const char kOnsetVolumeKey[] = "onset_volume";
@@ -37,6 +38,8 @@ Governor::Governor(const std::string& config, int input_channels)
   CHECK(config_dict) << "Governor config is not valid json: " << config;
   CHECK(config_dict->GetDouble(kOnsetVolumeKey, &onset_volume_));
   CHECK(config_dict->GetDouble(kClampMultiplierKey, &clamp_multiplier_));
+  CHECK_LE(onset_volume_, clamp_multiplier_);
+  CHECK_LE(onset_volume_, kMaxOnSetVolume);
   slew_volume_.SetVolume(1.0);
   LOG(INFO) << "Created a governor: onset_volume = " << onset_volume_
             << ", clamp_multiplier = " << clamp_multiplier_;
@@ -71,9 +74,12 @@ void Governor::ProcessFrames(float* data,
 }
 
 float Governor::GetGovernorMultiplier() {
-  // If |volume_| is greater than or "equal" to |onset_volume_|.
-  if (volume_ > onset_volume_ - kEpsilon) {
-    return clamp_multiplier_;
+  if (volume_ > onset_volume_) {
+    float effective_volume =
+        onset_volume_ + (volume_ - onset_volume_) *
+                            (clamp_multiplier_ - onset_volume_) /
+                            (1. - onset_volume_);
+    return effective_volume / volume_;
   }
   return 1.0;
 }

chromecast/media/cma/backend/mixer/post_processors/governor.h

@@ -16,13 +16,15 @@
 namespace chromecast {
 namespace media {
 
-// Provides a flat reduction in output volume if the input volume is above a
+// Provides linear reduction in output volume if the input volume is above a
 // given threshold.
 // Used to protect speakers at high output levels while providing dynamic range
 // at low output level.
 // The configuration string for this plugin is:
 //  {"onset_volume": |VOLUME_TO_CLAMP|, "clamp_multiplier": |CLAMP_MULTIPLIER|}
-// Input volumes > |VOLUME_TO_CLAMP| will be attenuated by |CLAMP_MULTIPLIER|.
+// Input volumes > |VOLUME_TO_CLAMP| will be attenuated by linear approximation,
+// changing from 0 (at VOLUME_TO_CLAMP) to |CLAMP_MULTIPLIER| (at 1.0).
+// |CLAMP_MULTIPLIER| must be >= |VOLUME_TO_CLAMP|.
 class Governor : public AudioPostProcessor2 {
  public:
   Governor(const std::string& config, int input_channels);

chromecast/media/cma/backend/mixer/post_processors/governor_unittest.cc

@@ -81,9 +81,6 @@ class GovernorTest : public ::testing::TestWithParam<float> {
 
 TEST_P(GovernorTest, ZeroVolume) {
   ProcessFrames(0.0f);
-  if (onset_volume_ <= 0.0f) {
-    ScaleData(expected_.data(), kNumFrames * kNumChannels, clamp_);
-  }
   CompareBuffers();
 }
 
@@ -95,15 +92,6 @@ TEST_P(GovernorTest, EpsilonBelowOnset) {
   CompareBuffers();
 }
 
-TEST_P(GovernorTest, EpsilonAboveOnset) {
-  // Approximately equaling is inclusive, thus needs more than one epsilon to
-  // make sure triggering volume change.
-  float volume = onset_volume_ + 2 * std::numeric_limits<float>::epsilon();
-  ProcessFrames(volume);
-  ScaleData(expected_.data(), kNumFrames * kNumChannels, clamp_);
-  CompareBuffers();
-}
-
 TEST_P(GovernorTest, MaxVolume) {
   ProcessFrames(1.0);
   if (onset_volume_ <= 1.0) {
@@ -114,29 +102,23 @@ TEST_P(GovernorTest, MaxVolume) {
 
 INSTANTIATE_TEST_SUITE_P(GovernorClampVolumeTest,
                          GovernorTest,
-                         ::testing::Values(0.0f, 0.1f, 0.5f, 0.9f, 1.0f, 1.1f));
+                         ::testing::Values(0.0f, 0.1f, 0.5f));
 
 // Default tests from post_processor_test
 TEST_P(PostProcessorTest, GovernorDelay) {
-  std::string config = MakeConfigString(1.0, 1.0);
+  std::string config = MakeConfigString(0.8, 0.9);
   auto pp = std::make_unique<Governor>(config, kNumChannels);
   TestDelay(pp.get(), sample_rate_);
 }
 
 TEST_P(PostProcessorTest, GovernorRinging) {
-  std::string config = MakeConfigString(1.0, 1.0);
+  std::string config = MakeConfigString(0.8, 0.9);
   auto pp = std::make_unique<Governor>(config, kNumChannels);
   TestRingingTime(pp.get(), sample_rate_);
 }
 
-TEST_P(PostProcessorTest, GovernorPassthrough) {
-  std::string config = MakeConfigString(1.0, 1.0);
-  auto pp = std::make_unique<Governor>(config, kNumChannels);
-  TestPassthrough(pp.get(), sample_rate_);
-}
-
 TEST_P(PostProcessorTest, GovernorBenchmark) {
-  std::string config = MakeConfigString(1.0, 1.0);
+  std::string config = MakeConfigString(0.8, 0.9);
   auto pp = std::make_unique<Governor>(config, kNumChannels);
   AudioProcessorBenchmark(pp.get(), sample_rate_);
 }