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// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// The EnergyEndpointer class finds likely speech onset and offset points.
// The implementation described here is about the simplest possible.
// It is based on timings of threshold crossings for overall signal
// RMS. It is suitable for light weight applications.
// As written, the basic idea is that one specifies intervals that
// must be occupied by super- and sub-threshold energy levels, and
// defers decisions re onset and offset times until these
// specifications have been met. Three basic intervals are tested: an
// onset window, a speech-on window, and an offset window. We require
// super-threshold to exceed some mimimum total durations in the onset
// and speech-on windows before declaring the speech onset time, and
// we specify a required sub-threshold residency in the offset window
// before declaring speech offset. As the various residency requirements are
// met, the EnergyEndpointer instance assumes various states, and can return the
// ID of these states to the client (see EpStatus below).
// The levels of the speech and background noise are continuously updated. It is
// important that the background noise level be estimated initially for
// robustness in noisy conditions. The first frames are assumed to be background
// noise and a fast update rate is used for the noise level. The duration for
// fast update is controlled by the fast_update_dur_ paramter.
// If used in noisy conditions, the endpointer should be started and run in the
// EnvironmentEstimation mode, for at least 200ms, before switching to
// UserInputMode.
// Audio feedback contamination can appear in the input audio, if not cut
// out or handled by echo cancellation. Audio feedback can trigger a false
// accept. The false accepts can be ignored by setting
// ep_contamination_rejection_period.
#include <stdint.h>
#include <memory>
#include <vector>
#include "base/memory/scoped_ptr.h"
#include "content/browser/speech/endpointer/energy_endpointer_params.h"
namespace content {
// Endpointer status codes
enum EpStatus {
class EnergyEndpointer {
// The default construction MUST be followed by Init(), before any
// other use can be made of the instance.
virtual ~EnergyEndpointer();
void Init(const EnergyEndpointerParams& params);
// Start the endpointer. This should be called at the beginning of a session.
void StartSession();
// Stop the endpointer.
void EndSession();
// Start environment estimation. Audio will be used for environment estimation
// i.e. noise level estimation.
void SetEnvironmentEstimationMode();
// Start user input. This should be called when the user indicates start of
// input, e.g. by pressing a button.
void SetUserInputMode();
// Computes the next input frame and modifies EnergyEndpointer status as
// appropriate based on the computation.
void ProcessAudioFrame(int64_t time_us,
const int16_t* samples,
int num_samples,
float* rms_out);
// Returns the current state of the EnergyEndpointer and the time
// corresponding to the most recently computed frame.
EpStatus Status(int64_t* status_time_us) const;
bool estimating_environment() const {
return estimating_environment_;
// Returns estimated noise level in dB.
float GetNoiseLevelDb() const;
class HistoryRing;
// Resets the endpointer internal state. If reset_threshold is true, the
// state will be reset completely, including adaptive thresholds and the
// removal of all history information.
void Restart(bool reset_threshold);
// Update internal speech and noise levels.
void UpdateLevels(float rms);
// Returns the number of frames (or frame number) corresponding to
// the 'time' (in seconds).
int TimeToFrame(float time) const;
EpStatus status_; // The current state of this instance.
float offset_confirm_dur_sec_; // max on time allowed to confirm POST_SPEECH
endpointer_time_us_; // Time of the most recently received audio frame.
fast_update_frames_; // Number of frames for initial level adaptation.
frame_counter_; // Number of frames seen. Used for initial adaptation.
float max_window_dur_; // Largest search window size (seconds)
float sample_rate_; // Sampling rate.
// Ring buffers to hold the speech activity history.
scoped_ptr<HistoryRing> history_;
// Configuration parameters.
EnergyEndpointerParams params_;
// RMS which must be exceeded to conclude frame is speech.
float decision_threshold_;
// Flag to indicate that audio should be used to estimate environment, prior
// to receiving user input.
bool estimating_environment_;
// Estimate of the background noise level. Used externally for UI feedback.
float noise_level_;
// An adaptive threshold used to update decision_threshold_ when appropriate.
float rms_adapt_;
// Start lag corresponds to the highest fundamental frequency.
int start_lag_;
// End lag corresponds to the lowest fundamental frequency.
int end_lag_;
// Time when mode switched from environment estimation to user input. This
// is used to time forced rejection of audio feedback contamination.
int64_t user_input_start_time_us_;
} // namespace content