onepole.h

/*
Copyright (c) 2020 Electrosmith, Corp, Emilie Gillet
 
Use of this source code is governed by an MIT-style
license that can be found in the LICENSE file or at
https://opensource.org/licenses/MIT.
*/
 
#ifndef DSY_ONEPOLE_H
#define DSY_ONEPOLE_H
 
#include "Utility/dsp.h"
#include <cmath>
#include <algorithm>
 
namespace daisysp
{
class OnePole
{
  public:
    OnePole() {}
    ~OnePole() {}
 
    enum FilterMode
    {
        FILTER_MODE_LOW_PASS,
        FILTER_MODE_HIGH_PASS
    };
 
    void Init()
    {
        Reset();
        mode_ = FILTER_MODE_LOW_PASS;
    }
 
    inline void Reset() { state_ = 0.0f; }
 
    inline void SetFrequency(float freq)
    {
        // Clip coefficient to about 100.
        freq = freq < 0.497f ? freq : 0.497f;
 
        g_  = tanf(PI_F * freq);
        gi_ = 1.f / (1.f + g_);
    }
 
    inline void SetFilterMode(FilterMode mode) { mode_ = mode; }
 
    inline float Process(float in)
    {
        float lp;
        lp     = (g_ * in + state_) * gi_;
        state_ = g_ * (in - lp) + lp;
 
        switch(mode_)
        {
            case FILTER_MODE_LOW_PASS: return lp;
            case FILTER_MODE_HIGH_PASS: return in - lp;
        }
 
        return 0.0f;
    }
 
    inline void ProcessBlock(float* in_out, size_t size)
    {
        while(size--)
        {
            *in_out = Process(*in_out);
            ++in_out;
        }
    }
 
  private:
    float      g_;
    float      gi_;
    float      state_;
    FilterMode mode_;
};
 
} // namespace daisysp
 
#endif // DSY_ONEPOLE_H