portapack-mayhem/firmware/common/dsp_iir.hpp

/*
 * Copyright (C) 2015 Jared Boone, ShareBrained Technology, Inc.
 *
 * This file is part of PortaPack.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2, or (at your option)
 * any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; see the file COPYING.  If not, write to
 * the Free Software Foundation, Inc., 51 Franklin Street,
 * Boston, MA 02110-1301, USA.
 */

#ifndef __DSP_IIR_H__
#define __DSP_IIR_H__

#include <array>

#include "dsp_types.hpp"

struct iir_biquad_config_t {
    std::array<float, 3> b;
    std::array<float, 3> a;
};

// 0..2 - b, 3..5 - a
typedef std::array<float, 6> iir_biquad_df2_config_t;

constexpr iir_biquad_config_t iir_config_passthrough{
    {{1.0f, 0.0f, 0.0f}},
    {{0.0f, 0.0f, 0.0f}},
};

constexpr iir_biquad_config_t iir_config_no_pass{
    {{0.0f, 0.0f, 0.0f}},
    {{0.0f, 0.0f, 0.0f}},
};

class IIRBiquadFilter {
   public:
    // http://www.musicdsp.org/files/Audio-EQ-Cookbook.txt
    constexpr IIRBiquadFilter()
        : IIRBiquadFilter(iir_config_no_pass) {
    }

    // Assume all coefficients are normalized so that a0=1.0
    constexpr IIRBiquadFilter(
        const iir_biquad_config_t& config)
        : config(config) {
    }

    void configure(const iir_biquad_config_t& new_config);

    void execute(const buffer_f32_t& buffer_in, const buffer_f32_t& buffer_out);
    void execute_in_place(const buffer_f32_t& buffer);

   private:
    iir_biquad_config_t config;
    std::array<float, 3> x{{0.0f, 0.0f, 0.0f}};
    std::array<float, 3> y{{0.0f, 0.0f, 0.0f}};
};

class IIRBiquadDF2Filter {
   public:
    void configure(const iir_biquad_df2_config_t& config);
    float execute(float z);

   private:
    float b0 = 0;
    float b1 = 0;
    float b2 = 0;
    float a1 = 0;
    float a2 = 0;

    float z0 = 0;
    float z1 = 0;
};

#endif /*__DSP_IIR_H__*/