tor-browser

gain_control.h (4633B)

---

/*
*  Copyright (c) 2018 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.
*/

#ifndef MODULES_AUDIO_PROCESSING_AGC_GAIN_CONTROL_H_
#define MODULES_AUDIO_PROCESSING_AGC_GAIN_CONTROL_H_

namespace webrtc {

// The automatic gain control (AGC) component brings the signal to an
// appropriate range. This is done by applying a digital gain directly and, in
// the analog mode, prescribing an analog gain to be applied at the audio HAL.
//
// Recommended to be enabled on the client-side.
class GainControl {
public:
 // When an analog mode is set, this must be called prior to `ProcessStream()`
 // to pass the current analog level from the audio HAL. Must be within the
 // range provided to `set_analog_level_limits()`.
 virtual int set_stream_analog_level(int level) = 0;

 // When an analog mode is set, this should be called after `ProcessStream()`
 // to obtain the recommended new analog level for the audio HAL. It is the
 // users responsibility to apply this level.
 virtual int stream_analog_level() const = 0;

 enum Mode {
   // Adaptive mode intended for use if an analog volume control is available
   // on the capture device. It will require the user to provide coupling
   // between the OS mixer controls and AGC through the `stream_analog_level()`
   // functions.
   //
   // It consists of an analog gain prescription for the audio device and a
   // digital compression stage.
   kAdaptiveAnalog,

   // Adaptive mode intended for situations in which an analog volume control
   // is unavailable. It operates in a similar fashion to the adaptive analog
   // mode, but with scaling instead applied in the digital domain. As with
   // the analog mode, it additionally uses a digital compression stage.
   kAdaptiveDigital,

   // Fixed mode which enables only the digital compression stage also used by
   // the two adaptive modes.
   //
   // It is distinguished from the adaptive modes by considering only a
   // short time-window of the input signal. It applies a fixed gain through
   // most of the input level range, and compresses (gradually reduces gain
   // with increasing level) the input signal at higher levels. This mode is
   // preferred on embedded devices where the capture signal level is
   // predictable, so that a known gain can be applied.
   kFixedDigital
 };

 virtual int set_mode(Mode mode) = 0;
 virtual Mode mode() const = 0;

 // Sets the target peak `level` (or envelope) of the AGC in dBFs (decibels
 // from digital full-scale). The convention is to use positive values. For
 // instance, passing in a value of 3 corresponds to -3 dBFs, or a target
 // level 3 dB below full-scale. Limited to [0, 31].
 //
 // TODO(ajm): use a negative value here instead, if/when VoE will similarly
 //            update its interface.
 virtual int set_target_level_dbfs(int level) = 0;
 virtual int target_level_dbfs() const = 0;

 // Sets the maximum `gain` the digital compression stage may apply, in dB. A
 // higher number corresponds to greater compression, while a value of 0 will
 // leave the signal uncompressed. Limited to [0, 90].
 virtual int set_compression_gain_db(int gain) = 0;
 virtual int compression_gain_db() const = 0;

 // When enabled, the compression stage will hard limit the signal to the
 // target level. Otherwise, the signal will be compressed but not limited
 // above the target level.
 virtual int enable_limiter(bool enable) = 0;
 virtual bool is_limiter_enabled() const = 0;

 // Sets the `minimum` and `maximum` analog levels of the audio capture device.
 // Must be set if and only if an analog mode is used. Limited to [0, 65535].
 virtual int set_analog_level_limits(int minimum, int maximum) = 0;
 virtual int analog_level_minimum() const = 0;
 virtual int analog_level_maximum() const = 0;

 // Returns true if the AGC has detected a saturation event (period where the
 // signal reaches digital full-scale) in the current frame and the analog
 // level cannot be reduced.
 //
 // This could be used as an indicator to reduce or disable analog mic gain at
 // the audio HAL.
 virtual bool stream_is_saturated() const = 0;

protected:
 virtual ~GainControl() {}
};
}  // namespace webrtc

#endif  // MODULES_AUDIO_PROCESSING_AGC_GAIN_CONTROL_H_