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86 lines
2.4 KiB
C
86 lines
2.4 KiB
C
/*!
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* Polyphonic synthesizer for microcontrollers. ADSR Envelope generator.
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* (C) 2017 Stuart Longland
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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 of the License, or
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* (at your option) 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; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston,
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* MA 02110-1301 USA
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*/
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#ifndef _ADSR_H
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#define _ADSR_H
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#include <stdint.h>
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/* ADSR states */
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#define ADSR_STATE_IDLE (0x00)
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#define ADSR_STATE_DELAY_INIT (0x10)
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#define ADSR_STATE_DELAY_EXPIRE (0x1f)
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#define ADSR_STATE_ATTACK_INIT (0x20)
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#define ADSR_STATE_ATTACK (0x21)
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#define ADSR_STATE_ATTACK_EXPIRE (0x2f)
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#define ADSR_STATE_DECAY_INIT (0x30)
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#define ADSR_STATE_DECAY (0x31)
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#define ADSR_STATE_DECAY_EXPIRE (0x3f)
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#define ADSR_STATE_SUSTAIN_INIT (0x40)
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#define ADSR_STATE_SUSTAIN_EXPIRE (0x4f)
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#define ADSR_STATE_RELEASE_INIT (0x50)
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#define ADSR_STATE_RELEASE (0x51)
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#define ADSR_STATE_RELEASE_EXPIRE (0x5f)
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/*!
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* ADSR Envelope Generator data. 20 bytes.
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*/
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struct adsr_env_gen_t {
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/*! Time to next event, samples */
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uint32_t next_event;
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/*! Time step, samples */
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uint16_t time_step;
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/*! Time scale, samples per unit */
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uint32_t time_scale;
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/*! Delay period, time units */
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uint8_t delay_time;
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/*! Attack period, time units */
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uint8_t attack_time;
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/*! Decay period, time units */
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uint8_t decay_time;
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/*! Sustain period, time units */
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uint8_t sustain_time;
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/*! Release period, time units */
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uint8_t release_time;
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/*! Attack peak amplitude */
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uint8_t peak_amp;
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/*! Sustain amplitude */
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uint8_t sustain_amp;
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/*! Present amplitude */
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uint8_t amplitude;
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/*! ADSR state */
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uint8_t state;
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/*! ADSR counter */
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uint8_t counter;
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};
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/*!
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* Reset the ADSR state ready for the next note
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*/
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void adsr_reset(struct adsr_env_gen_t* const adsr);
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/*!
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* Compute the ADSR amplitude
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*/
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uint8_t adsr_next(struct adsr_env_gen_t* const adsr);
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#endif
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/*
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* vim: set sw=8 ts=8 noet si tw=72
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*/
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