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ADSR-based synthesizer for microcontrollers

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Stuart Longland 2017-04-08 18:54:00 +10:00
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GNU GENERAL PUBLIC LICENSE
Version 2, June 1991
Copyright (C) 1989, 1991 Free Software Foundation, Inc.
51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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# Compiler definitions
CROSS_COMPILE ?= avr-
CC = $(CROSS_COMPILE)gcc
AR = $(CROSS_COMPILE)ar
OBJCOPY = $(CROSS_COMPILE)objcopy
OBJDUMP = $(CROSS_COMPILE)objdump
SIZE = $(CROSS_COMPILE)size
MCU ?= attiny85
CFLAGS ?= -g -mmcu=$(MCU) -O3 -Werror -Woverflow
CPPFLAGS ?= -DF_CPU=$(FREQ) -D_POLY_CFG=\"poly_cfg.h\"
LDFLAGS ?= -mmcu=$(MCU) -O3 -Wl,--as-needed
PROG ?= avrdude
PROG_ARGS ?= -B 10 -c stk500v2 -P /dev/ttyACM0
PROG_DEV ?= t85
BINDIR ?= bin
SRCDIR ?= .
OBJDIR ?= obj
LFUSE=0xc1
HFUSE=0xdf
EFUSE=0xff
FREQ=16000000
.PHONY: setfuse all clean
-include local.mk
all: bindir/synth.hex
%.hex: %.elf
$(OBJCOPY) -j .text -j .data -O ihex $< $@
$(BINDIR)/synth.elf: $(OBJDIR)/main.o $(OBJDIR)/poly.a
@[ -d $(BINDIR) ] || mkdir $(BINDIR)
$(CC) -g -o $@ $(LDFLAGS) $^
$(OBJDIR)/poly.a: $(OBJDIR)/adsr.o $(OBJDIR)/waveform.o
$(AR) rcs $@ $^
$(OBJDIR)/%.o: $(SRCDIR)/%.c
@[ -d $(OBJDIR) ] || mkdir $(OBJDIR)
$(CC) -o $@ -c $(CPPFLAGS) $(CFLAGS) $<
clean:
-rm -fr $(OBJDIR) $(BINDIR)
%.ihex: %.elf
$(OBJCOPY) -j .text -j .data -O ihex $^ $@
%.pgm: %.ihex
$(PROG) $(PROG_ARGS) -p $(PROG_DEV) -U flash:w:$^:i
setfuse:
$(PROG) $(PROG_ARGS) -p $(PROG_DEV) \
-U lfuse:w:$(LFUSE):m \
-U hfuse:w:$(HFUSE):m \
-U efuse:w:$(EFUSE):m

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ADSR-based Polyphonic Synthesizer
=================================
This project is intended to be a polyphonic synthesizer for use in
embedded microcontrollers. It features multi-voice synthesis for multiple
channels.
The synthesis is inspired from the highly regarded MOS Technologies 6581
"SID" chip, which supported up to 3 voices each producing either a
square wave, triangle wave or sawtooth wave output and hardware
attack/decay/sustain/release envelope generation.
This tries to achieve the same thing in software.
Code is presently a work-in-progress.

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/*!
* Polyphonic synthesizer for microcontrollers. ADSR Envelope 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 "adsr.h"
#include <stdlib.h>
#ifdef __AVR_ARCH__
#include <avr/pgmspace.h>
#endif
/* ADSR attack/decay adjustments */
#define ADSR_EXP_AMP_FACTOR (6)
#define ADSR_EXP_SHIFT (-8)
#define ADSR_EXP_TIME_FACTOR (1)
#define ADSR_LIN_AMP_FACTOR (6)
#define ADSR_DECAY_OFFSET (16)
/*!
* ADSR Attack amplitude exponential shift.
*/
static uint8_t adsr_attack_shift(uint8_t sample) {
return (sample + ADSR_EXP_SHIFT)/ADSR_EXP_TIME_FACTOR
- ADSR_EXP_AMP_FACTOR;
}
/*!
* ADSR Release amplitude exponential shift.
*/
static uint8_t adsr_release_shift(uint8_t sample) {
return adsr_attack_shift(ADSR_DECAY_OFFSET - sample);
}
/*!
* Reset the ADSR state ready for the next note
*/
void adsr_reset(struct adsr_env_gen_t* const adsr) {
adsr->next_event = 0;
adsr->state = ADSR_STATE_IDLE;
}
/*!
* Compute the ADSR amplitude
*/
uint8_t adsr_next(struct adsr_env_gen_t* const adsr) {
if (adsr->next_event) {
/* Still waiting for next event */
adsr->next_event--;
return adsr->amplitude;
}
/*
* We use if statements here since we might want to jump
* between states. This lets us do that more easily.
*/
if (adsr->state == ADSR_STATE_IDLE) {
/* Are registers set up? */
if (!adsr->time_scale)
return 0;
if (!(adsr->delay_time || adsr->attack_time
|| adsr->decay_time || adsr->release_time))
return 0;
if (!(adsr->peak_amp || adsr->sustain_amp))
return 0;
/* All good */
if (adsr->delay_time)
adsr->state = ADSR_STATE_DELAY_INIT;
else
adsr->state = ADSR_STATE_DELAY_EXPIRE;
}
if (adsr->state == ADSR_STATE_DELAY_INIT) {
/* Setting up a delay */
adsr->amplitude = 0;
adsr->next_event = adsr->time_scale
* adsr->delay_time;
adsr->state = ADSR_STATE_DELAY_EXPIRE;
/* Wait for delay */
return adsr->amplitude;
}
if (adsr->state == ADSR_STATE_DELAY_EXPIRE) {
/* Delay has expired */
if (adsr->attack_time)
adsr->state = ADSR_STATE_ATTACK_INIT;
else
adsr->state = ADSR_STATE_ATTACK_EXPIRE;
}
if (adsr->state == ADSR_STATE_ATTACK_INIT) {
/* Attack is divided into 16 segments */
adsr->time_step = (uint16_t)((adsr->attack_time
* adsr->time_scale) >> 4);
adsr->counter = 16;
adsr->next_event = adsr->time_step;
adsr->state = ADSR_STATE_ATTACK;
}
if (adsr->state == ADSR_STATE_ATTACK) {
if (adsr->counter) {
/* Change of amplitude */
uint16_t lin_amp = (16-adsr->counter)
* adsr->peak_amp;
adsr->amplitude = lin_amp
>> ADSR_LIN_AMP_FACTOR;
adsr->amplitude += adsr->peak_amp >>
adsr_attack_shift(adsr->counter);
/* Go around again */
adsr->counter--;
adsr->next_event = adsr->time_step;
return adsr->amplitude;
} else {
adsr->state = ADSR_STATE_ATTACK_EXPIRE;
}
}
if (adsr->state == ADSR_STATE_ATTACK_EXPIRE) {
if (adsr->decay_time)
adsr->state = ADSR_STATE_DECAY_INIT;
else
adsr->state = ADSR_STATE_DECAY_EXPIRE;
}
if (adsr->state == ADSR_STATE_DECAY_INIT) {
/* We should be at full amplitude */
adsr->amplitude = adsr->peak_amp;
adsr->time_step = (uint16_t)((adsr->decay_time
* adsr->time_scale) >> 4);
adsr->counter = 16;
adsr->next_event = adsr->time_step;
adsr->state = ADSR_STATE_DECAY;
}
if (adsr->state == ADSR_STATE_DECAY) {
if (adsr->counter) {
/* Linear decrease in amplitude */
uint16_t delta = adsr->peak_amp
- adsr->sustain_amp;
delta *= adsr->counter;
delta >>= 4;
adsr->amplitude = adsr->sustain_amp + delta;
adsr->next_event = adsr->time_step;
adsr->counter--;
} else {
adsr->state = ADSR_STATE_DECAY_EXPIRE;
}
}
if (adsr->state == ADSR_STATE_DECAY_EXPIRE) {
if (adsr->sustain_time)
adsr->state = ADSR_STATE_SUSTAIN_INIT;
else
adsr->state = ADSR_STATE_SUSTAIN_EXPIRE;
}
if (adsr->state == ADSR_STATE_SUSTAIN_INIT) {
adsr->amplitude = adsr->sustain_amp;
adsr->next_event = adsr->time_scale
* adsr->sustain_time;
adsr->state = ADSR_STATE_SUSTAIN_EXPIRE;
/* Wait for delay */
return adsr->amplitude;
}
if (adsr->state == ADSR_STATE_SUSTAIN_EXPIRE) {
if (adsr->release_time)
adsr->state = ADSR_STATE_RELEASE_INIT;
else
adsr->state = ADSR_STATE_RELEASE_EXPIRE;
}
if (adsr->state == ADSR_STATE_RELEASE_INIT) {
adsr->time_step = (uint16_t)((adsr->release_time
* adsr->time_scale) >> 4);
adsr->counter = 16;
adsr->next_event = adsr->time_step;
adsr->state = ADSR_STATE_RELEASE;
}
if (adsr->state == ADSR_STATE_RELEASE) {
if (adsr->counter) {
/* Change of amplitude */
uint16_t lin_amp = adsr->counter
* adsr->peak_amp;
adsr->amplitude = lin_amp
>> ADSR_LIN_AMP_FACTOR;
adsr->amplitude += adsr->peak_amp >>
adsr_release_shift(adsr->counter);
/* Go around again */
adsr->counter--;
adsr->next_event = adsr->time_step;
} else {
adsr->state = ADSR_STATE_RELEASE_EXPIRE;
}
}
if (adsr->state == ADSR_STATE_RELEASE_EXPIRE) {
/* Reset the state */
adsr->state = ADSR_STATE_IDLE;
adsr->amplitude = 0;
}
return adsr->amplitude;
}
/*
* vim: set sw=8 ts=8 noet si tw=72
*/

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/*!
* Polyphonic synthesizer for microcontrollers. ADSR Envelope 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
*/
#ifndef _ADSR_H
#define _ADSR_H
#include <stdint.h>
/* ADSR states */
#define ADSR_STATE_IDLE (0x00)
#define ADSR_STATE_DELAY_INIT (0x10)
#define ADSR_STATE_DELAY_EXPIRE (0x1f)
#define ADSR_STATE_ATTACK_INIT (0x20)
#define ADSR_STATE_ATTACK (0x21)
#define ADSR_STATE_ATTACK_EXPIRE (0x2f)
#define ADSR_STATE_DECAY_INIT (0x30)
#define ADSR_STATE_DECAY (0x31)
#define ADSR_STATE_DECAY_EXPIRE (0x3f)
#define ADSR_STATE_SUSTAIN_INIT (0x40)
#define ADSR_STATE_SUSTAIN_EXPIRE (0x4f)
#define ADSR_STATE_RELEASE_INIT (0x50)
#define ADSR_STATE_RELEASE (0x51)
#define ADSR_STATE_RELEASE_EXPIRE (0x5f)
/*!
* ADSR Envelope Generator data. 20 bytes.
*/
struct adsr_env_gen_t {
/*! Time to next event, samples */
uint32_t next_event;
/*! Time step, samples */
uint16_t time_step;
/*! Time scale, samples per unit */
uint32_t time_scale;
/*! Delay period, time units */
uint8_t delay_time;
/*! Attack period, time units */
uint8_t attack_time;
/*! Decay period, time units */
uint8_t decay_time;
/*! Sustain period, time units */
uint8_t sustain_time;
/*! Release period, time units */
uint8_t release_time;
/*! Attack peak amplitude */
uint8_t peak_amp;
/*! Sustain amplitude */
uint8_t sustain_amp;
/*! Present amplitude */
uint8_t amplitude;
/*! ADSR state */
uint8_t state;
/*! ADSR counter */
uint8_t counter;
};
/*!
* Reset the ADSR state ready for the next note
*/
void adsr_reset(struct adsr_env_gen_t* const adsr);
/*!
* Compute the ADSR amplitude
*/
uint8_t adsr_next(struct adsr_env_gen_t* const adsr);
#endif
/*
* vim: set sw=8 ts=8 noet si tw=72
*/

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/*!
* Polyphonic synthesizer for microcontrollers.
* (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
*/
#ifndef _SYNTH_H
#define _SYNTH_H
#include "voice.h"
/*
* _POLY_CFG_H is a definition that can be given when compiling poly.c
* and firmware code to define a header file that contains definitions for
* the Polyphonic synthesizer.
*/
#ifdef SYNTH_CFG
#include SYNTH_CFG
#endif
#ifndef SYNTH_FREQ
/*!
* Sample rate for the synthesizer: this needs to be declared in the
* application.
*/
extern const uint16_t __attribute__((weak)) synth_freq;
#else
#define synth_freq SYNTH_FREQ
#endif
/*!
* Polyphonic synthesizer structure
*/
struct poly_synth_t {
/*! Pointer to voices. There may be up to 16 voices referenced. */
struct voice_ch_t* const voice;
/*!
* Bit-field enabling given voices. This allows selective turning
* on and off of given voice channels. If the corresponding bit is
* not a 1, then that channel is not computed.
*
* Note no bounds checking is done, if you have only defined 4
* channels, then only set bits 0-3, don't set bits 4 onwards here.
*/
uintptr_t enable;
/*!
* Bit-field muting given voices. This allows for selective adding
* of voices to the overall output. If a field is 1, then that voice
* channel is not included. (Note, disabled channels are *also*
* not included.)
*/
uintptr_t mute;
};
/*!
* Compute the next synthesizer sample.
*/
static inline int8_t poly_synth_next(struct poly_synth_t* const synth) {
int16_t sample = 0;
uintptr_t mask = 1;
uint8_t idx = 0;
while (mask) {
if (synth->enable & mask) {
/* Channel is enabled */
int8_t ch_sample = voice_ch_next(
&(synth->voice[idx]));
if (!(synth->mute & mask))
sample += ch_sample;
}
idx++;
mask <<= 1;
}
/* Handle clipping */
if (sample > INT8_MAX)
sample = INT8_MAX;
else if (sample < INT8_MIN)
sample = INT8_MIN;
return sample;
};
#endif
/*
* vim: set sw=8 ts=8 noet si tw=72
*/

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/*!
* Polyphonic synthesizer for microcontrollers. Voice generation.
* (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 "adsr.h"
/*!
* Voice channel state. 30 bytes.
*/
struct voice_ch_t {
/*!
* ADSR Envelope generator state.
*/
struct adsr_env_gen_t adsr;
/*!
* Waveform generator state.
*/
struct voice_wf_gen_t wf;
};
/*!
* Compute the next voice channel sample.
*/
inline static int8_t voice_ch_next(struct voice_ch_t* const voice) {
uint8_t amplitude = adsr_next(&(voice->adsr));
if (!amplitude)
return 0;
int16_t value = voice_wf_next(&(voice->wf));
value *= amplitude;
/* Saturation handling */
if (value < INT8_MIN)
return INT8_MIN;
else if (value > INT8_MAX)
return INT8_MAX;
else
return value;
}
/*
* vim: set sw=8 ts=8 noet si tw=72
*/

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/*!
* 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 <stdlib.h>
/* Waveform generation modes */
#define VOICE_MODE_DC (0)
#define VOICE_MODE_SQUARE (1)
#define VOICE_MODE_SAWTOOTH (2)
#define VOICE_MODE_TRIANGLE (3)
#define VOICE_MODE_NOISE (4)
/* Amplitude scaling */
#define VOICE_WF_AMP_SCALE (8)
int8_t voice_wf_next(struct voice_wf_gen_t* const wf_gen) {
switch(wf_gen->mode) {
case VOICE_MODE_DC:
return wf_gen->amplitude;
case VOICE_MODE_NOISE:
wf_gen->sample = (rand() /
(RAND_MAX/512)) - 256;
wf_gen->sample *= wf_gen->amplitude;
break;
case VOICE_MODE_SQUARE:
if (!wf_gen->period_remain) {
/* Swap value */
wf_gen->sample = -wf_gen->sample;
wf_gen->period_remain = wf_gen->period;
} else {
wf_gen->period_remain--;
}
break;
case VOICE_MODE_SAWTOOTH:
if (!wf_gen->period_remain) {
/* Back to -amplitude */
wf_gen->sample = -wf_gen->amplitude
<< VOICE_WF_AMP_SCALE;
wf_gen->period_remain = wf_gen->period;
} else {
wf_gen->sample += wf_gen->step;
wf_gen->period_remain--;
}
break;
case VOICE_MODE_TRIANGLE:
if (!wf_gen->period_remain) {
/* 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--;
}
break;
}
return wf_gen->sample >> VOICE_WF_AMP_SCALE;
}
/* Compute frequency period (sawtooth wave) */
static uint8_t voice_wf_calc_sawtooth_period(uint16_t freq) {
return (synth_freq / freq);
}
/* Compute frequency period (square/triangle wave) */
static uint8_t voice_wf_calc_square_period(uint16_t freq) {
return voice_wf_calc_sawtooth_period(freq) >> 1;
}
void voice_wf_set_dc(struct voice_wf_gen_t* const wf_gen,
uint8_t amplitude) {
wf_gen->mode = VOICE_MODE_DC;
wf_gen->amplitude = amplitude;
}
void voice_wf_set_square(struct voice_wf_gen_t* const wf_gen,
uint16_t freq, uint8_t amplitude) {
wf_gen->mode = VOICE_MODE_SQUARE;
wf_gen->amplitude = amplitude << VOICE_WF_AMP_SCALE;
wf_gen->period = voice_wf_calc_square_period(freq);
wf_gen->period_remain = wf_gen->period;
wf_gen->sample = wf_gen->amplitude;
}
void voice_wf_set_sawtooth(struct voice_wf_gen_t* const wf_gen,
uint16_t freq, uint8_t amplitude) {
wf_gen->mode = VOICE_MODE_SAWTOOTH;
wf_gen->sample = wf_gen->amplitude << VOICE_WF_AMP_SCALE;
wf_gen->period = voice_wf_calc_sawtooth_period(freq);
wf_gen->period_remain = wf_gen->period;
wf_gen->amplitude = -wf_gen->sample;
wf_gen->step = ((int32_t)(wf_gen->amplitude << 1)) / wf_gen->period;
}
void voice_wf_set_triangle(struct voice_wf_gen_t* const wf_gen,
uint16_t freq, uint8_t amplitude) {
wf_gen->mode = VOICE_MODE_TRIANGLE;
wf_gen->sample = wf_gen->amplitude << VOICE_WF_AMP_SCALE;
wf_gen->period = voice_wf_calc_square_period(freq);
wf_gen->period_remain = wf_gen->period;
wf_gen->amplitude = -wf_gen->sample;
wf_gen->step = ((int32_t)(wf_gen->amplitude << 1)) / wf_gen->period;
}
void voice_wf_set_noise(struct voice_wf_gen_t* const wf_gen,
uint8_t amplitude) {
wf_gen->mode = VOICE_MODE_SQUARE;
wf_gen->amplitude = amplitude;
}
/*
* vim: set sw=8 ts=8 noet si tw=72
*/

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/*!
* 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
*/
#ifndef _WAVEFORM_H
#define _WAVEFORM_H
#include <stdint.h>
/*!
* Waveform generator state. 10 bytes.
*/
struct voice_wf_gen_t {
/*! Waveform output sample in fixed-point */
int16_t sample;
/*! Amplitude sample in fixed point */
int16_t amplitude;
/*! Samples to next waveform period */
uint16_t period_remain;
/*!
* Period duration in samples.
* (Half period for SQUARE and TRIANGLE)
*/
uint16_t period;
/*! Amplitude step for TRIANGLE and SAWTOOTH */
int8_t step;
/*! Waveform generation mode */
uint8_t mode;
};
/*!
* Configure the generator for a DC offset synthesis.
*/
void voice_wf_set_dc(struct voice_wf_gen_t* const wf_gen,
uint8_t amplitude);
/*!
* Configure the generator for square wave synthesis.
*/
void voice_wf_set_square(struct voice_wf_gen_t* const wf_gen,
uint16_t freq, uint8_t amplitude);
/*!
* Configure the generator for sawtooth wave synthesis.
*/
void voice_wf_set_sawtooth(struct voice_wf_gen_t* const wf_gen,
uint16_t freq, uint8_t amplitude);
/*!
* Configure the generator for sawtooth wave synthesis.
*/
void voice_wf_set_triangle(struct voice_wf_gen_t* const wf_gen,
uint16_t freq, uint8_t amplitude);
/*!
* Configure the generator for pseudorandom noise synthesis.
*/
void voice_wf_set_noise(struct voice_wf_gen_t* const wf_gen,
uint8_t amplitude);
/*!
* Retrieve the next sample from the generator.
*/
int8_t voice_wf_next(struct voice_wf_gen_t* const wf_gen);
#endif
/*
* vim: set sw=8 ts=8 noet si tw=72
*/