portapack-mayhem/firmware/baseband/dsp_iir.hpp
2015-07-08 08:39:24 -07:00

69 lines
1.7 KiB
C++

/*
* 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"
class IIRBiquadFilter {
public:
// http://www.musicdsp.org/files/Audio-EQ-Cookbook.txt
// Assume all coefficients are normalized so that a0=1.0
constexpr IIRBiquadFilter(
std::array<float, 3> b,
std::array<float, 3> a
) : b(b),
a(a)
{
}
void execute(buffer_s16_t buffer) {
for(size_t i=0; i<buffer.count; i++) {
buffer.p[i] = execute_sample(buffer.p[i]);
}
}
private:
const std::array<float, 3> b;
const std::array<float, 3> a;
std::array<float, 3> x { { 0.0f, 0.0f, 0.0f } };
std::array<float, 3> y { { 0.0f, 0.0f, 0.0f } };
float execute_sample(const float in) {
x[0] = x[1];
x[1] = x[2];
x[2] = in;
y[0] = y[1];
y[1] = y[2];
y[2] = b[0] * x[2] + b[1] * x[1] + b[2] * x[0]
- a[1] * y[1] - a[2] * y[0];
return y[2];
}
};
#endif/*__DSP_IIR_H__*/