atinysynth/waveform.c

/*!
 * Polyphonic synthesizer for microcontrollers.  Voice waveform generator.
 * (C) 2017 Stuart Longland
 *
 * 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 of the License, 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; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston,
 * MA  02110-1301  USA
 */

#include "waveform.h"
#include "synth.h"
#include "debug.h"
#include <stdlib.h>

/* Amplitude scaling */
#define VOICE_WF_AMP_SCALE	(8)

/*!
 * Number of fractional bits for `period` and `period_remain`.
 * This allows tuned notes even in lower sampling frequencies.
 * The integer part (12 bits) is wide enough to render a 20Hz
 * note on the higher 48kHz sampling frequency.
 */
#define PERIOD_FP_SCALE 	(4)

int8_t voice_wf_next(struct voice_wf_gen_t* const wf_gen) {
	switch(wf_gen->mode) {
		case VOICE_MODE_DC:
			_DPRINTF("wf=%p mode=DC amp=%d\n",
					wf_gen, wf_gen->amplitude);
			return wf_gen->amplitude;
		case VOICE_MODE_NOISE:
			wf_gen->sample = (rand() /
				(RAND_MAX/512)) - 256;
			wf_gen->sample *= wf_gen->amplitude;
			_DPRINTF("wf=%p mode=NOISE amp=%d → sample=%d\n",
					wf_gen, wf_gen->amplitude,
					wf_gen->sample);
			break;
		case VOICE_MODE_SQUARE:
			if ((wf_gen->period_remain >> PERIOD_FP_SCALE) == 0) {
				/* Swap value */
				wf_gen->sample = -wf_gen->sample;
				wf_gen->period_remain += wf_gen->period;
			}
			wf_gen->period_remain -= (1 << PERIOD_FP_SCALE);
			_DPRINTF("wf=%p mode=SQUARE amp=%d rem=%d "
					"→ sample=%d\n",
					wf_gen, wf_gen->amplitude,
					wf_gen->period_remain,
					wf_gen->sample);
			break;
		case VOICE_MODE_SAWTOOTH:
			if ((wf_gen->period_remain >> PERIOD_FP_SCALE) == 0) {
				/* Back to -amplitude */
				wf_gen->sample = -wf_gen->amplitude;
				wf_gen->period_remain += wf_gen->period;
			} else {
				wf_gen->sample += wf_gen->step;
			}
			wf_gen->period_remain -= (1 << PERIOD_FP_SCALE);
			_DPRINTF("wf=%p mode=SAWTOOTH amp=%d rem=%d step=%d "
					"→ sample=%d\n",
					wf_gen, wf_gen->amplitude,
					wf_gen->period_remain, wf_gen->step,
					wf_gen->sample);
			break;
		case VOICE_MODE_TRIANGLE:
			if ((wf_gen->period_remain >> PERIOD_FP_SCALE) == 0) {
				/* Switch direction */
				if (wf_gen->step > 0)
					wf_gen->sample = wf_gen->amplitude;
				else
					wf_gen->sample = -wf_gen->amplitude;
				wf_gen->step = -wf_gen->step;
				wf_gen->period_remain += wf_gen->period;
			} else {
				wf_gen->sample += wf_gen->step;
			}
			wf_gen->period_remain -= (1 << PERIOD_FP_SCALE);
			_DPRINTF("wf=%p mode=TRIANGLE amp=%d rem=%d step=%d "
					"→ sample=%d\n",
					wf_gen, wf_gen->amplitude,
					wf_gen->period_remain, wf_gen->step,
					wf_gen->sample);
			break;
	}

	return wf_gen->sample >> VOICE_WF_AMP_SCALE;
}

/* Compute frequency period (sawtooth wave) */
uint16_t voice_wf_freq_to_period(uint16_t freq) {
	/* Use 16-bit 12.4 fixed point */
	return (((uint32_t)synth_freq << PERIOD_FP_SCALE) / freq);
}

/* Compute frequency period (square/triangle wave) */
static uint16_t voice_wf_to_square_period(uint16_t period) {
	return period >> 1;
}

void voice_wf_set_dc(struct voice_wf_gen_t* const wf_gen,
		int8_t amplitude) {
	wf_gen->mode = VOICE_MODE_DC;
	wf_gen->amplitude = amplitude;
}

static void voice_wf_set_square_p(struct voice_wf_gen_t* const wf_gen,
		uint16_t period, int8_t amplitude) {
	wf_gen->mode = VOICE_MODE_SQUARE;
	wf_gen->amplitude = (int16_t)amplitude << VOICE_WF_AMP_SCALE;
	wf_gen->period = voice_wf_to_square_period(period);
	wf_gen->period_remain = wf_gen->period;
	wf_gen->sample = wf_gen->amplitude;
	_DPRINTF("wf=%p INIT mode=SQUARE amp=%d per=%d rem=%d "
			"→ sample=%d\n",
			wf_gen, wf_gen->amplitude, wf_gen->period,
			wf_gen->period_remain,
			wf_gen->sample);
}

void voice_wf_set_square(struct voice_wf_gen_t* const wf_gen,
		uint16_t freq, int8_t amplitude) {
	uint16_t period = voice_wf_freq_to_period(freq);
	voice_wf_set_square_p(wf_gen, period, amplitude);
}

static void voice_wf_set_sawtooth_p(struct voice_wf_gen_t* const wf_gen,
		uint16_t period, int8_t amplitude) {
	wf_gen->mode = VOICE_MODE_SAWTOOTH;
	wf_gen->sample = -(int16_t)amplitude << VOICE_WF_AMP_SCALE;
	wf_gen->period = period;
	wf_gen->period_remain = wf_gen->period;
	wf_gen->amplitude = -wf_gen->sample;
	wf_gen->step = (wf_gen->amplitude / (wf_gen->period >> PERIOD_FP_SCALE)) << 1;
	_DPRINTF("wf=%p INIT mode=SAWTOOTH amp=%d per=%d step=%d rem=%d "
			"→ sample=%d\n",
			wf_gen, wf_gen->amplitude, wf_gen->period,
			wf_gen->step, wf_gen->period_remain,
			wf_gen->sample);
}

void voice_wf_set_sawtooth(struct voice_wf_gen_t* const wf_gen,
		uint16_t freq, int8_t amplitude) {
	uint16_t period = voice_wf_freq_to_period(freq);
	voice_wf_set_sawtooth_p(wf_gen, period, amplitude);
}

static void voice_wf_set_triangle_p(struct voice_wf_gen_t* const wf_gen,
		uint16_t period, int8_t amplitude) {
	wf_gen->mode = VOICE_MODE_TRIANGLE;
	wf_gen->sample = -(int16_t)amplitude << VOICE_WF_AMP_SCALE;
	wf_gen->period = voice_wf_to_square_period(period);
	wf_gen->period_remain = wf_gen->period;
	wf_gen->amplitude = -wf_gen->sample;
	wf_gen->step = (wf_gen->amplitude / (wf_gen->period >> PERIOD_FP_SCALE)) << 1;
	_DPRINTF("wf=%p INIT mode=TRIANGLE amp=%d per=%d step=%d rem=%d "
			"→ sample=%d\n",
			wf_gen, wf_gen->amplitude, wf_gen->period,
			wf_gen->step, wf_gen->period_remain,
			wf_gen->sample);
}

void voice_wf_set_triangle(struct voice_wf_gen_t* const wf_gen,
		uint16_t freq, int8_t amplitude) {
	uint16_t period = voice_wf_freq_to_period(freq);
	voice_wf_set_triangle_p(wf_gen, period, amplitude);
}

void voice_wf_set_noise(struct voice_wf_gen_t* const wf_gen,
		int8_t amplitude) {
	wf_gen->mode = VOICE_MODE_NOISE;
	wf_gen->amplitude = amplitude;
}

void voice_wf_set(struct voice_wf_gen_t* const wf_gen, struct voice_wf_def_t* const wf_def) {
	switch (wf_def->mode) {
		case VOICE_MODE_DC:
			voice_wf_set_dc(wf_gen, wf_def->amplitude);
			break;
		case VOICE_MODE_SQUARE:
			voice_wf_set_square_p(wf_gen, wf_def->period, wf_def->amplitude);
			break;
		case VOICE_MODE_SAWTOOTH:
			voice_wf_set_sawtooth_p(wf_gen, wf_def->period, wf_def->amplitude);
			break;
		case VOICE_MODE_TRIANGLE:
			voice_wf_set_triangle_p(wf_gen, wf_def->period, wf_def->amplitude);
			break;
		case VOICE_MODE_NOISE:
			voice_wf_set_noise(wf_gen, wf_def->amplitude);
			break;
	}
}

/*
 * vim: set sw=8 ts=8 noet si tw=72
 */