modules/audio_processing/agc/clipping_predictor.cc - src - Git at Google

 /*
  *  Copyright (c) 2021 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/agc/clipping_predictor.h"

 #include <algorithm>
 #include <memory>

 #include "common_audio/include/audio_util.h"
 #include "modules/audio_processing/agc/clipping_predictor_level_buffer.h"
 #include "modules/audio_processing/agc/gain_map_internal.h"
 #include "rtc_base/checks.h"
 #include "rtc_base/logging.h"
 #include "rtc_base/numerics/safe_minmax.h"

 namespace webrtc {
 namespace {

 constexpr int kClippingPredictorMaxGainChange = 15;

 // Estimates the new level from the gain error; a copy of the function
 // `LevelFromGainError` in agc_manager_direct.cc.
 int LevelFromGainError(int gain_error,
                        int level,
                        int min_mic_level,
                        int max_mic_level) {
   RTC_DCHECK_GE(level, 0);
   RTC_DCHECK_LE(level, max_mic_level);
   if (gain_error == 0) {
     return level;
   }
   int new_level = level;
   if (gain_error > 0) {
     while (kGainMap[new_level] - kGainMap[level] < gain_error &&
            new_level < max_mic_level) {
       ++new_level;
     }
   } else {
     while (kGainMap[new_level] - kGainMap[level] > gain_error &&
            new_level > min_mic_level) {
       --new_level;
     }
   }
   return new_level;
 }

 float ComputeCrestFactor(const ClippingPredictorLevelBuffer::Level& level) {
   const float crest_factor =
       FloatS16ToDbfs(level.max) - FloatS16ToDbfs(std::sqrt(level.average));
   return crest_factor;
 }

 // Crest factor-based clipping prediction and clipped level step estimation.
 class ClippingEventPredictor : public ClippingPredictor {
  public:
   // ClippingEventPredictor with `num_channels` channels (limited to values
   // higher than zero); window size `window_length` and reference window size
   // `reference_window_length` (both referring to the number of frames in the
   // respective sliding windows and limited to values higher than zero);
   // reference window delay `reference_window_delay` (delay in frames, limited
   // to values zero and higher with an additional requirement of
   // `window_length` < `reference_window_length` + reference_window_delay`);
   // and an estimation peak threshold `clipping_threshold` and a crest factor
   // drop threshold `crest_factor_margin` (both in dB).
   ClippingEventPredictor(int num_channels,
                          int window_length,
                          int reference_window_length,
                          int reference_window_delay,
                          float clipping_threshold,
                          float crest_factor_margin)
       : window_length_(window_length),
         reference_window_length_(reference_window_length),
         reference_window_delay_(reference_window_delay),
         clipping_threshold_(clipping_threshold),
         crest_factor_margin_(crest_factor_margin) {
     RTC_DCHECK_GT(num_channels, 0);
     RTC_DCHECK_GT(window_length, 0);
     RTC_DCHECK_GT(reference_window_length, 0);
     RTC_DCHECK_GE(reference_window_delay, 0);
     RTC_DCHECK_GT(reference_window_length + reference_window_delay,
                   window_length);
     const int buffer_length = GetMinFramesProcessed();
     RTC_DCHECK_GT(buffer_length, 0);
     for (int i = 0; i < num_channels; ++i) {
       ch_buffers_.push_back(
           std::make_unique<ClippingPredictorLevelBuffer>(buffer_length));
     }
   }

   ClippingEventPredictor(const ClippingEventPredictor&) = delete;
   ClippingEventPredictor& operator=(const ClippingEventPredictor&) = delete;
   ~ClippingEventPredictor() {}

   void Reset() {
     const int num_channels = ch_buffers_.size();
     for (int i = 0; i < num_channels; ++i) {
       ch_buffers_[i]->Reset();
     }
   }

   // Analyzes a frame of audio and stores the framewise metrics in
   // `ch_buffers_`.
   void Analyze(const AudioFrameView<const float>& frame) {
     const int num_channels = frame.num_channels();
     RTC_DCHECK_EQ(num_channels, ch_buffers_.size());
     const int samples_per_channel = frame.samples_per_channel();
     RTC_DCHECK_GT(samples_per_channel, 0);
     for (int channel = 0; channel < num_channels; ++channel) {
       float sum_squares = 0.0f;
       float peak = 0.0f;
       for (const auto& sample : frame.channel(channel)) {
         sum_squares += sample * sample;
         peak = std::max(std::fabs(sample), peak);
       }
       ch_buffers_[channel]->Push(
           {sum_squares / static_cast<float>(samples_per_channel), peak});
     }
   }

   // Estimates the analog gain adjustment for channel `channel` using a
   // sliding window over the frame-wise metrics in `ch_buffers_`. Returns an
   // estimate for the clipped level step equal to `default_clipped_level_step_`
   // if at least `GetMinFramesProcessed()` frames have been processed since the
   // last reset and a clipping event is predicted. `level`, `min_mic_level`, and
   // `max_mic_level` are limited to [0, 255] and `default_step` to [1, 255].
   absl::optional<int> EstimateClippedLevelStep(int channel,
                                                int level,
                                                int default_step,
                                                int min_mic_level,
                                                int max_mic_level) const {
     RTC_CHECK_GE(channel, 0);
     RTC_CHECK_LT(channel, ch_buffers_.size());
     RTC_DCHECK_GE(level, 0);
     RTC_DCHECK_LE(level, 255);
     RTC_DCHECK_GT(default_step, 0);
     RTC_DCHECK_LE(default_step, 255);
     RTC_DCHECK_GE(min_mic_level, 0);
     RTC_DCHECK_LE(min_mic_level, 255);
     RTC_DCHECK_GE(max_mic_level, 0);
     RTC_DCHECK_LE(max_mic_level, 255);
     if (level <= min_mic_level) {
       return absl::nullopt;
     }
     if (PredictClippingEvent(channel)) {
       const int new_level =
           rtc::SafeClamp(level - default_step, min_mic_level, max_mic_level);
       const int step = level - new_level;
       if (step > 0) {
         return step;
       }
     }
     return absl::nullopt;
   }

  private:
   int GetMinFramesProcessed() const {
     return reference_window_delay_ + reference_window_length_;
   }

   // Predicts clipping events based on the processed audio frames. Returns
   // true if a clipping event is likely.
   bool PredictClippingEvent(int channel) const {
     const auto metrics =
         ch_buffers_[channel]->ComputePartialMetrics(0, window_length_);
     if (!metrics.has_value() ||
         !(FloatS16ToDbfs(metrics.value().max) > clipping_threshold_)) {
       return false;
     }
     const auto reference_metrics = ch_buffers_[channel]->ComputePartialMetrics(
         reference_window_delay_, reference_window_length_);
     if (!reference_metrics.has_value()) {
       return false;
     }
     const float crest_factor = ComputeCrestFactor(metrics.value());
     const float reference_crest_factor =
         ComputeCrestFactor(reference_metrics.value());
     if (crest_factor < reference_crest_factor - crest_factor_margin_) {
       return true;
     }
     return false;
   }

   std::vector<std::unique_ptr<ClippingPredictorLevelBuffer>> ch_buffers_;
   const int window_length_;
   const int reference_window_length_;
   const int reference_window_delay_;
   const float clipping_threshold_;
   const float crest_factor_margin_;
 };

 // Performs crest factor-based clipping peak prediction.
 class ClippingPeakPredictor : public ClippingPredictor {
  public:
   // Ctor. ClippingPeakPredictor with `num_channels` channels (limited to values
   // higher than zero); window size `window_length` and reference window size
   // `reference_window_length` (both referring to the number of frames in the
   // respective sliding windows and limited to values higher than zero);
   // reference window delay `reference_window_delay` (delay in frames, limited
   // to values zero and higher with an additional requirement of
   // `window_length` < `reference_window_length` + reference_window_delay`);
   // and a clipping prediction threshold `clipping_threshold` (in dB). Adaptive
   // clipped level step estimation is used if `adaptive_step_estimation` is
   // true.
   explicit ClippingPeakPredictor(int num_channels,
                                  int window_length,
                                  int reference_window_length,
                                  int reference_window_delay,
                                  int clipping_threshold,
                                  bool adaptive_step_estimation)
       : window_length_(window_length),
         reference_window_length_(reference_window_length),
         reference_window_delay_(reference_window_delay),
         clipping_threshold_(clipping_threshold),
         adaptive_step_estimation_(adaptive_step_estimation) {
     RTC_DCHECK_GT(num_channels, 0);
     RTC_DCHECK_GT(window_length, 0);
     RTC_DCHECK_GT(reference_window_length, 0);
     RTC_DCHECK_GE(reference_window_delay, 0);
     RTC_DCHECK_GT(reference_window_length + reference_window_delay,
                   window_length);
     const int buffer_length = GetMinFramesProcessed();
     RTC_DCHECK_GT(buffer_length, 0);
     for (int i = 0; i < num_channels; ++i) {
       ch_buffers_.push_back(
           std::make_unique<ClippingPredictorLevelBuffer>(buffer_length));
     }
   }

   ClippingPeakPredictor(const ClippingPeakPredictor&) = delete;
   ClippingPeakPredictor& operator=(const ClippingPeakPredictor&) = delete;
   ~ClippingPeakPredictor() {}

   void Reset() {
     const int num_channels = ch_buffers_.size();
     for (int i = 0; i < num_channels; ++i) {
       ch_buffers_[i]->Reset();
     }
   }

   // Analyzes a frame of audio and stores the framewise metrics in
   // `ch_buffers_`.
   void Analyze(const AudioFrameView<const float>& frame) {
     const int num_channels = frame.num_channels();
     RTC_DCHECK_EQ(num_channels, ch_buffers_.size());
     const int samples_per_channel = frame.samples_per_channel();
     RTC_DCHECK_GT(samples_per_channel, 0);
     for (int channel = 0; channel < num_channels; ++channel) {
       float sum_squares = 0.0f;
       float peak = 0.0f;
       for (const auto& sample : frame.channel(channel)) {
         sum_squares += sample * sample;
         peak = std::max(std::fabs(sample), peak);
       }
       ch_buffers_[channel]->Push(
           {sum_squares / static_cast<float>(samples_per_channel), peak});
     }
   }

   // Estimates the analog gain adjustment for channel `channel` using a
   // sliding window over the frame-wise metrics in `ch_buffers_`. Returns an
   // estimate for the clipped level step (equal to
   // `default_clipped_level_step_` if `adaptive_estimation_` is false) if at
   // least `GetMinFramesProcessed()` frames have been processed since the last
   // reset and a clipping event is predicted. `level`, `min_mic_level`, and
   // `max_mic_level` are limited to [0, 255] and `default_step` to [1, 255].
   absl::optional<int> EstimateClippedLevelStep(int channel,
                                                int level,
                                                int default_step,
                                                int min_mic_level,
                                                int max_mic_level) const {
     RTC_DCHECK_GE(channel, 0);
     RTC_DCHECK_LT(channel, ch_buffers_.size());
     RTC_DCHECK_GE(level, 0);
     RTC_DCHECK_LE(level, 255);
     RTC_DCHECK_GT(default_step, 0);
     RTC_DCHECK_LE(default_step, 255);
     RTC_DCHECK_GE(min_mic_level, 0);
     RTC_DCHECK_LE(min_mic_level, 255);
     RTC_DCHECK_GE(max_mic_level, 0);
     RTC_DCHECK_LE(max_mic_level, 255);
     if (level <= min_mic_level) {
       return absl::nullopt;
     }
     absl::optional<float> estimate_db = EstimatePeakValue(channel);
     if (estimate_db.has_value() && estimate_db.value() > clipping_threshold_) {
       int step = 0;
       if (!adaptive_step_estimation_) {
         step = default_step;
       } else {
         const int estimated_gain_change =
             rtc::SafeClamp(-static_cast<int>(std::ceil(estimate_db.value())),
                            -kClippingPredictorMaxGainChange, 0);
         step =
             std::max(level - LevelFromGainError(estimated_gain_change, level,
                                                 min_mic_level, max_mic_level),
                      default_step);
       }
       const int new_level =
           rtc::SafeClamp(level - step, min_mic_level, max_mic_level);
       if (level > new_level) {
         return level - new_level;
       }
     }
     return absl::nullopt;
   }

  private:
   int GetMinFramesProcessed() {
     return reference_window_delay_ + reference_window_length_;
   }

   // Predicts clipping sample peaks based on the processed audio frames.
   // Returns the estimated peak value if clipping is predicted. Otherwise
   // returns absl::nullopt.
   absl::optional<float> EstimatePeakValue(int channel) const {
     const auto reference_metrics = ch_buffers_[channel]->ComputePartialMetrics(
         reference_window_delay_, reference_window_length_);
     if (!reference_metrics.has_value()) {
       return absl::nullopt;
     }
     const auto metrics =
         ch_buffers_[channel]->ComputePartialMetrics(0, window_length_);
     if (!metrics.has_value() ||
         !(FloatS16ToDbfs(metrics.value().max) > clipping_threshold_)) {
       return absl::nullopt;
     }
     const float reference_crest_factor =
         ComputeCrestFactor(reference_metrics.value());
     const float& mean_squares = metrics.value().average;
     const float projected_peak =
         reference_crest_factor + FloatS16ToDbfs(std::sqrt(mean_squares));
     return projected_peak;
   }

   std::vector<std::unique_ptr<ClippingPredictorLevelBuffer>> ch_buffers_;
   const int window_length_;
   const int reference_window_length_;
   const int reference_window_delay_;
   const int clipping_threshold_;
   const bool adaptive_step_estimation_;
 };

 }  // namespace

 std::unique_ptr<ClippingPredictor> CreateClippingPredictor(
     int num_channels,
     const AudioProcessing::Config::GainController1::AnalogGainController::
         ClippingPredictor& config) {
   if (!config.enabled) {
     RTC_LOG(LS_INFO) << "[agc] Clipping prediction disabled.";
     return nullptr;
   }
   RTC_LOG(LS_INFO) << "[agc] Clipping prediction enabled.";
   using ClippingPredictorMode = AudioProcessing::Config::GainController1::
       AnalogGainController::ClippingPredictor::Mode;
   switch (config.mode) {
     case ClippingPredictorMode::kClippingEventPrediction:
       return std::make_unique<ClippingEventPredictor>(
           num_channels, config.window_length, config.reference_window_length,
           config.reference_window_delay, config.clipping_threshold,
           config.crest_factor_margin);
     case ClippingPredictorMode::kAdaptiveStepClippingPeakPrediction:
       return std::make_unique<ClippingPeakPredictor>(
           num_channels, config.window_length, config.reference_window_length,
           config.reference_window_delay, config.clipping_threshold,
           /*adaptive_step_estimation=*/true);
     case ClippingPredictorMode::kFixedStepClippingPeakPrediction:
       return std::make_unique<ClippingPeakPredictor>(
           num_channels, config.window_length, config.reference_window_length,
           config.reference_window_delay, config.clipping_threshold,
           /*adaptive_step_estimation=*/false);
   }
   RTC_DCHECK_NOTREACHED();
 }

 }  // namespace webrtc
	/*
	* Copyright (c) 2021 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/agc/clipping_predictor.h"

	#include <algorithm>
	#include <memory>

	#include "common_audio/include/audio_util.h"
	#include "modules/audio_processing/agc/clipping_predictor_level_buffer.h"
	#include "modules/audio_processing/agc/gain_map_internal.h"
	#include "rtc_base/checks.h"
	#include "rtc_base/logging.h"
	#include "rtc_base/numerics/safe_minmax.h"

	namespace webrtc {
	namespace {

	constexpr int kClippingPredictorMaxGainChange = 15;

	// Estimates the new level from the gain error; a copy of the function
	// `LevelFromGainError` in agc_manager_direct.cc.
	int LevelFromGainError(int gain_error,
	int level,
	int min_mic_level,
	int max_mic_level) {
	RTC_DCHECK_GE(level, 0);
	RTC_DCHECK_LE(level, max_mic_level);
	if (gain_error == 0) {
	return level;
	}
	int new_level = level;
	if (gain_error > 0) {
	while (kGainMap[new_level] - kGainMap[level] < gain_error &&
	new_level < max_mic_level) {
	++new_level;
	}
	} else {
	while (kGainMap[new_level] - kGainMap[level] > gain_error &&
	new_level > min_mic_level) {
	--new_level;
	}
	}
	return new_level;
	}

	float ComputeCrestFactor(const ClippingPredictorLevelBuffer::Level& level) {
	const float crest_factor =
	FloatS16ToDbfs(level.max) - FloatS16ToDbfs(std::sqrt(level.average));
	return crest_factor;
	}

	// Crest factor-based clipping prediction and clipped level step estimation.
	class ClippingEventPredictor : public ClippingPredictor {
	public:
	// ClippingEventPredictor with `num_channels` channels (limited to values
	// higher than zero); window size `window_length` and reference window size
	// `reference_window_length` (both referring to the number of frames in the
	// respective sliding windows and limited to values higher than zero);
	// reference window delay `reference_window_delay` (delay in frames, limited
	// to values zero and higher with an additional requirement of
	// `window_length` < `reference_window_length` + reference_window_delay`);
	// and an estimation peak threshold `clipping_threshold` and a crest factor
	// drop threshold `crest_factor_margin` (both in dB).
	ClippingEventPredictor(int num_channels,
	int window_length,
	int reference_window_length,
	int reference_window_delay,
	float clipping_threshold,
	float crest_factor_margin)
	: window_length_(window_length),
	reference_window_length_(reference_window_length),
	reference_window_delay_(reference_window_delay),
	clipping_threshold_(clipping_threshold),
	crest_factor_margin_(crest_factor_margin) {
	RTC_DCHECK_GT(num_channels, 0);
	RTC_DCHECK_GT(window_length, 0);
	RTC_DCHECK_GT(reference_window_length, 0);
	RTC_DCHECK_GE(reference_window_delay, 0);
	RTC_DCHECK_GT(reference_window_length + reference_window_delay,
	window_length);
	const int buffer_length = GetMinFramesProcessed();
	RTC_DCHECK_GT(buffer_length, 0);
	for (int i = 0; i < num_channels; ++i) {
	ch_buffers_.push_back(
	std::make_unique<ClippingPredictorLevelBuffer>(buffer_length));
	}
	}

	ClippingEventPredictor(const ClippingEventPredictor&) = delete;
	ClippingEventPredictor& operator=(const ClippingEventPredictor&) = delete;
	~ClippingEventPredictor() {}

	void Reset() {
	const int num_channels = ch_buffers_.size();
	for (int i = 0; i < num_channels; ++i) {
	ch_buffers_[i]->Reset();
	}
	}

	// Analyzes a frame of audio and stores the framewise metrics in
	// `ch_buffers_`.
	void Analyze(const AudioFrameView<const float>& frame) {
	const int num_channels = frame.num_channels();
	RTC_DCHECK_EQ(num_channels, ch_buffers_.size());
	const int samples_per_channel = frame.samples_per_channel();
	RTC_DCHECK_GT(samples_per_channel, 0);
	for (int channel = 0; channel < num_channels; ++channel) {
	float sum_squares = 0.0f;
	float peak = 0.0f;
	for (const auto& sample : frame.channel(channel)) {
	sum_squares += sample * sample;
	peak = std::max(std::fabs(sample), peak);
	}
	ch_buffers_[channel]->Push(
	{sum_squares / static_cast<float>(samples_per_channel), peak});
	}
	}

	// Estimates the analog gain adjustment for channel `channel` using a
	// sliding window over the frame-wise metrics in `ch_buffers_`. Returns an
	// estimate for the clipped level step equal to `default_clipped_level_step_`
	// if at least `GetMinFramesProcessed()` frames have been processed since the
	// last reset and a clipping event is predicted. `level`, `min_mic_level`, and
	// `max_mic_level` are limited to [0, 255] and `default_step` to [1, 255].
	absl::optional<int> EstimateClippedLevelStep(int channel,
	int level,
	int default_step,
	int min_mic_level,
	int max_mic_level) const {
	RTC_CHECK_GE(channel, 0);
	RTC_CHECK_LT(channel, ch_buffers_.size());
	RTC_DCHECK_GE(level, 0);
	RTC_DCHECK_LE(level, 255);
	RTC_DCHECK_GT(default_step, 0);
	RTC_DCHECK_LE(default_step, 255);
	RTC_DCHECK_GE(min_mic_level, 0);
	RTC_DCHECK_LE(min_mic_level, 255);
	RTC_DCHECK_GE(max_mic_level, 0);
	RTC_DCHECK_LE(max_mic_level, 255);
	if (level <= min_mic_level) {
	return absl::nullopt;
	}
	if (PredictClippingEvent(channel)) {
	const int new_level =
	rtc::SafeClamp(level - default_step, min_mic_level, max_mic_level);
	const int step = level - new_level;
	if (step > 0) {
	return step;
	}
	}
	return absl::nullopt;
	}

	private:
	int GetMinFramesProcessed() const {
	return reference_window_delay_ + reference_window_length_;
	}

	// Predicts clipping events based on the processed audio frames. Returns
	// true if a clipping event is likely.
	bool PredictClippingEvent(int channel) const {
	const auto metrics =
	ch_buffers_[channel]->ComputePartialMetrics(0, window_length_);
	if (!metrics.has_value() \|\|
	!(FloatS16ToDbfs(metrics.value().max) > clipping_threshold_)) {
	return false;
	}
	const auto reference_metrics = ch_buffers_[channel]->ComputePartialMetrics(
	reference_window_delay_, reference_window_length_);
	if (!reference_metrics.has_value()) {
	return false;
	}
	const float crest_factor = ComputeCrestFactor(metrics.value());
	const float reference_crest_factor =
	ComputeCrestFactor(reference_metrics.value());
	if (crest_factor < reference_crest_factor - crest_factor_margin_) {
	return true;
	}
	return false;
	}

	std::vector<std::unique_ptr<ClippingPredictorLevelBuffer>> ch_buffers_;
	const int window_length_;
	const int reference_window_length_;
	const int reference_window_delay_;
	const float clipping_threshold_;
	const float crest_factor_margin_;
	};

	// Performs crest factor-based clipping peak prediction.
	class ClippingPeakPredictor : public ClippingPredictor {
	public:
	// Ctor. ClippingPeakPredictor with `num_channels` channels (limited to values
	// higher than zero); window size `window_length` and reference window size
	// `reference_window_length` (both referring to the number of frames in the
	// respective sliding windows and limited to values higher than zero);
	// reference window delay `reference_window_delay` (delay in frames, limited
	// to values zero and higher with an additional requirement of
	// `window_length` < `reference_window_length` + reference_window_delay`);
	// and a clipping prediction threshold `clipping_threshold` (in dB). Adaptive
	// clipped level step estimation is used if `adaptive_step_estimation` is
	// true.
	explicit ClippingPeakPredictor(int num_channels,
	int window_length,
	int reference_window_length,
	int reference_window_delay,
	int clipping_threshold,
	bool adaptive_step_estimation)
	: window_length_(window_length),
	reference_window_length_(reference_window_length),
	reference_window_delay_(reference_window_delay),
	clipping_threshold_(clipping_threshold),
	adaptive_step_estimation_(adaptive_step_estimation) {
	RTC_DCHECK_GT(num_channels, 0);
	RTC_DCHECK_GT(window_length, 0);
	RTC_DCHECK_GT(reference_window_length, 0);
	RTC_DCHECK_GE(reference_window_delay, 0);
	RTC_DCHECK_GT(reference_window_length + reference_window_delay,
	window_length);
	const int buffer_length = GetMinFramesProcessed();
	RTC_DCHECK_GT(buffer_length, 0);
	for (int i = 0; i < num_channels; ++i) {
	ch_buffers_.push_back(
	std::make_unique<ClippingPredictorLevelBuffer>(buffer_length));
	}
	}

	ClippingPeakPredictor(const ClippingPeakPredictor&) = delete;
	ClippingPeakPredictor& operator=(const ClippingPeakPredictor&) = delete;
	~ClippingPeakPredictor() {}

	void Reset() {
	const int num_channels = ch_buffers_.size();
	for (int i = 0; i < num_channels; ++i) {
	ch_buffers_[i]->Reset();
	}
	}

	// Analyzes a frame of audio and stores the framewise metrics in
	// `ch_buffers_`.
	void Analyze(const AudioFrameView<const float>& frame) {
	const int num_channels = frame.num_channels();
	RTC_DCHECK_EQ(num_channels, ch_buffers_.size());
	const int samples_per_channel = frame.samples_per_channel();
	RTC_DCHECK_GT(samples_per_channel, 0);
	for (int channel = 0; channel < num_channels; ++channel) {
	float sum_squares = 0.0f;
	float peak = 0.0f;
	for (const auto& sample : frame.channel(channel)) {
	sum_squares += sample * sample;
	peak = std::max(std::fabs(sample), peak);
	}
	ch_buffers_[channel]->Push(
	{sum_squares / static_cast<float>(samples_per_channel), peak});
	}
	}

	// Estimates the analog gain adjustment for channel `channel` using a
	// sliding window over the frame-wise metrics in `ch_buffers_`. Returns an
	// estimate for the clipped level step (equal to
	// `default_clipped_level_step_` if `adaptive_estimation_` is false) if at
	// least `GetMinFramesProcessed()` frames have been processed since the last
	// reset and a clipping event is predicted. `level`, `min_mic_level`, and
	// `max_mic_level` are limited to [0, 255] and `default_step` to [1, 255].
	absl::optional<int> EstimateClippedLevelStep(int channel,
	int level,
	int default_step,
	int min_mic_level,
	int max_mic_level) const {
	RTC_DCHECK_GE(channel, 0);
	RTC_DCHECK_LT(channel, ch_buffers_.size());
	RTC_DCHECK_GE(level, 0);
	RTC_DCHECK_LE(level, 255);
	RTC_DCHECK_GT(default_step, 0);
	RTC_DCHECK_LE(default_step, 255);
	RTC_DCHECK_GE(min_mic_level, 0);
	RTC_DCHECK_LE(min_mic_level, 255);
	RTC_DCHECK_GE(max_mic_level, 0);
	RTC_DCHECK_LE(max_mic_level, 255);
	if (level <= min_mic_level) {
	return absl::nullopt;
	}
	absl::optional<float> estimate_db = EstimatePeakValue(channel);
	if (estimate_db.has_value() && estimate_db.value() > clipping_threshold_) {
	int step = 0;
	if (!adaptive_step_estimation_) {
	step = default_step;
	} else {
	const int estimated_gain_change =
	rtc::SafeClamp(-static_cast<int>(std::ceil(estimate_db.value())),
	-kClippingPredictorMaxGainChange, 0);
	step =
	std::max(level - LevelFromGainError(estimated_gain_change, level,
	min_mic_level, max_mic_level),
	default_step);
	}
	const int new_level =
	rtc::SafeClamp(level - step, min_mic_level, max_mic_level);
	if (level > new_level) {
	return level - new_level;
	}
	}
	return absl::nullopt;
	}

	private:
	int GetMinFramesProcessed() {
	return reference_window_delay_ + reference_window_length_;
	}

	// Predicts clipping sample peaks based on the processed audio frames.
	// Returns the estimated peak value if clipping is predicted. Otherwise
	// returns absl::nullopt.
	absl::optional<float> EstimatePeakValue(int channel) const {
	const auto reference_metrics = ch_buffers_[channel]->ComputePartialMetrics(
	reference_window_delay_, reference_window_length_);
	if (!reference_metrics.has_value()) {
	return absl::nullopt;
	}
	const auto metrics =
	ch_buffers_[channel]->ComputePartialMetrics(0, window_length_);
	if (!metrics.has_value() \|\|
	!(FloatS16ToDbfs(metrics.value().max) > clipping_threshold_)) {
	return absl::nullopt;
	}
	const float reference_crest_factor =
	ComputeCrestFactor(reference_metrics.value());
	const float& mean_squares = metrics.value().average;
	const float projected_peak =
	reference_crest_factor + FloatS16ToDbfs(std::sqrt(mean_squares));
	return projected_peak;
	}

	std::vector<std::unique_ptr<ClippingPredictorLevelBuffer>> ch_buffers_;
	const int window_length_;
	const int reference_window_length_;
	const int reference_window_delay_;
	const int clipping_threshold_;
	const bool adaptive_step_estimation_;
	};

	} // namespace

	std::unique_ptr<ClippingPredictor> CreateClippingPredictor(
	int num_channels,
	const AudioProcessing::Config::GainController1::AnalogGainController::
	ClippingPredictor& config) {
	if (!config.enabled) {
	RTC_LOG(LS_INFO) << "[agc] Clipping prediction disabled.";
	return nullptr;
	}
	RTC_LOG(LS_INFO) << "[agc] Clipping prediction enabled.";
	using ClippingPredictorMode = AudioProcessing::Config::GainController1::
	AnalogGainController::ClippingPredictor::Mode;
	switch (config.mode) {
	case ClippingPredictorMode::kClippingEventPrediction:
	return std::make_unique<ClippingEventPredictor>(
	num_channels, config.window_length, config.reference_window_length,
	config.reference_window_delay, config.clipping_threshold,
	config.crest_factor_margin);
	case ClippingPredictorMode::kAdaptiveStepClippingPeakPrediction:
	return std::make_unique<ClippingPeakPredictor>(
	num_channels, config.window_length, config.reference_window_length,
	config.reference_window_delay, config.clipping_threshold,
	/adaptive_step_estimation=/true);
	case ClippingPredictorMode::kFixedStepClippingPeakPrediction:
	return std::make_unique<ClippingPeakPredictor>(
	num_channels, config.window_length, config.reference_window_length,
	config.reference_window_delay, config.clipping_threshold,
	/adaptive_step_estimation=/false);
	}
	RTC_DCHECK_NOTREACHED();
	}

	} // namespace webrtc