gain_control.h - mozsearch

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/*

 *  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_