freq_estimator.h

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/*
 * Copyright (c) 2015 Roc Streaming authors
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 */
 
//! @file roc_audio/freq_estimator.h
//! @brief Frequency estimator.
 
#ifndef ROC_AUDIO_FREQ_ESTIMATOR_H_
#define ROC_AUDIO_FREQ_ESTIMATOR_H_
 
#include "roc_audio/freq_estimator_decim.h"
#include "roc_audio/sample.h"
#include "roc_core/noncopyable.h"
#include "roc_packet/units.h"
 
namespace roc {
namespace audio {
 
//! FreqEstimator paremeter preset.
enum FreqEstimatorProfile {
    //! Fast and responsive tuning.
    //! Good for lower network latency and jitter.
    FreqEstimatorProfile_Responsive,
 
    //! Slow and smooth tuning.
    //! Good for higher network latency and jitter.
    FreqEstimatorProfile_Gradual
};
 
//! FreqEstimator tunable parameters.
struct FreqEstimatorConfig {
    double P; //!< Proportional gain of PI-controller.
    double I; //!< Integral gain of PI-controller.
 
    //! How much downsample input value (latency buffer size) on the first stage.
    //! Must be less or equal to fe_decim_factor_max and must be greater than zero.
    size_t decimation_factor1;
 
    //! How much downsample input value on the second stage. Must be less or equal
    //! to fe_decim_factor_max. Could be zero to disable the second decimation stage.
    size_t decimation_factor2;
 
    FreqEstimatorConfig()
        : P(0)
        , I(0)
        , decimation_factor1(0)
        , decimation_factor2(0) {
    }
};
 
//! Evaluates sender's frequency to receivers's frequency ratio.
//! @remarks
//!  We provide FreqEstimator with traget latency and periodically update it with
//!  the actual latency. In response, FreqEstimator computes frequency coefficient,
//!  the ratio of sender to receiver frequency. This coefficient is then set as
//!  the scaling factor of the resampler, which in result compensates the frequency
//!  difference and moves the latency closer to its target value.
class FreqEstimator : public core::NonCopyable<> {
public:
    //! Initialize.
    //!
    //! @b Parameters
    //!  - @p profile defines configuration preset.
    //!  - @p target_latency defines latency we want to archive.
    FreqEstimator(FreqEstimatorProfile profile,
                  packet::stream_timestamp_t target_latency);
 
    //! Get current frequecy coefficient.
    float freq_coeff() const;
 
    //! Compute new value of frequency coefficient.
    void update(packet::stream_timestamp_t current_latency);
 
private:
    bool run_decimators_(packet::stream_timestamp_t current, double& filtered);
    double run_controller_(double current);
 
    const FreqEstimatorConfig config_;
    const double target_; // Target latency.
 
    double dec1_casc_buff_[fe_decim_len];
    size_t dec1_ind_;
 
    double dec2_casc_buff_[fe_decim_len];
    size_t dec2_ind_;
 
    size_t samples_counter_; // Input samples counter.
    double accum_;           // Integrator value.
 
    double coeff_; // Current frequency coefficient value.
};
 
} // namespace audio
} // namespace roc
 
#endif // ROC_AUDIO_FREQ_ESTIMATOR_H_