audio_cv_meter.h

// Copyright 2014 Emilie Gillet.
//
// Author: Emilie Gillet (emilie.o.gillet@gmail.com)
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
// 
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
// 
// See http://creativecommons.org/licenses/MIT/ for more information.
//
// -----------------------------------------------------------------------------
//
// Discriminate an ADC signal into audio or CV ; and provide RMS stats.

#ifndef STREAMS_AUDIO_CV_METER_H_
#define STREAMS_AUDIO_CV_METER_H_

#include "stmlib/stmlib.h"

namespace streams {

class AudioCvMeter {
 public:
  AudioCvMeter() { }
  ~AudioCvMeter() { }
  
  void Init() {
    peak_ = 0;
    
    zero_crossing_interval_ = 0;
    average_zero_crossing_interval_ = 0;

    previous_sample_ = 0;
    cv_ = false;
  }
  
  void Process(int32_t sample) {
    if ((sample >> 1) * previous_sample_ < 0 ||
        zero_crossing_interval_ >= 4096) {
      int32_t error = zero_crossing_interval_ - average_zero_crossing_interval_;
      average_zero_crossing_interval_ += error >> 3;
      zero_crossing_interval_ = 0;
    } else {
      ++zero_crossing_interval_;
    }
    
    if (cv_ && average_zero_crossing_interval_ < 200) {
      cv_ = false;
    } else if (!cv_ && average_zero_crossing_interval_ > 400) {
      cv_ = true;
    }
    
    previous_sample_ = sample;
    
    if (sample < 0) {
      sample = -sample;
    }
    int32_t error = sample - peak_;
    int32_t coefficient = 33;  // 250ms at 1kHz
    if (error > 0) {
      coefficient = 809;  // 10ms at 1kHz
    }
    peak_ += error * coefficient >> 15;
  }
  
  inline bool cv() const { return cv_; }
  inline int32_t peak() const { return peak_; }

 private:
  bool cv_;
  int32_t peak_;
  int32_t zero_crossing_interval_;
  int32_t average_zero_crossing_interval_;
  int32_t previous_sample_;
  
  DISALLOW_COPY_AND_ASSIGN(AudioCvMeter);
};

}  // namespace streams

#endif  // STREAMS_AUDIO_CV_METER_H_