mirror of
https://github.com/eried/portapack-mayhem.git
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87 lines
2.3 KiB
C++
87 lines
2.3 KiB
C++
/*
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* Copyright (C) 2020 Belousov Oleg
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*
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* This file is part of PortaPack.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2, or (at your option)
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* any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; see the file COPYING. If not, write to
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* the Free Software Foundation, Inc., 51 Franklin Street,
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* Boston, MA 02110-1301, USA.
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*/
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#include "dsp_hilbert.hpp"
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#include "dsp_sos_config.hpp"
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namespace dsp {
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HilbertTransform::HilbertTransform() {
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n = 0;
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sos_input.configure(half_band_lpf_config);
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sos_i.configure(half_band_lpf_config);
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sos_q.configure(half_band_lpf_config);
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}
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void HilbertTransform::execute(float in, float& out_i, float& out_q) {
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// Synthesized Hilbert Transform, it is implemented based on 1/2 band LPF and later freq shift fs/4, achieving a H.T_BW of transmitted = fs/2 ;
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// Half_band LPF means a LP filter with f_cut_off = fs/4; Half band = Half max band = 1/2 * fs_max = 1/2 x f_Nyquist = 1/2 * fs/2 = fs/4
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float a = 0, b = 0;
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float in_filtered = sos_input.execute(in) * 1.0f; // Anti-aliasing LPF at fs/4 mic audio filter front-end.
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switch (n) {
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case 0:
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a = in_filtered;
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b = 0;
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break;
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case 1:
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a = 0;
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b = -in_filtered;
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break;
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case 2:
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a = -in_filtered;
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b = 0;
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break;
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case 3:
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a = 0;
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b = in_filtered;
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break;
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}
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float i = sos_i.execute(a) * 2.0f;
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float q = sos_q.execute(b) * 2.0f;
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switch (n) {
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case 0:
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out_i = i;
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out_q = q;
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break;
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case 1:
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out_i = -q;
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out_q = i;
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break;
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case 2:
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out_i = -i;
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out_q = -q;
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break;
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case 3:
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out_i = q;
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out_q = -i;
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break;
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}
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n = (n + 1) % 4;
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}
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} /* namespace dsp */
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