ref: 36a83aede9accc17bf02d97d2ac7d1c306e0eff7
dir: /src/synth.c/
/* libSoX synth - Synthesizer Effect.
*
* Copyright (c) 2001-2009 SoX contributors
* Copyright (c) Jan 2001 Carsten Borchardt
*
* This source code is freely redistributable and may be used for any purpose.
* This copyright notice must be maintained. The authors are not responsible
* for the consequences of using this software.
*
* Except for synth types: pluck, tpdf, & brownnoise, and sweep types: linear
* square & exp, which are:
*
* Copyright (c) 2006-2009 robs@users.sourceforge.net
*
* This library is free software; you can redistribute it and/or modify it
* under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation; either version 2.1 of the License, or (at
* your option) any later version.
*
* This library 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 Lesser
* General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this library; if not, write to the Free Software Foundation,
* Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include "sox_i.h"
#include <string.h>
#include <ctype.h>
typedef enum {
synth_sine,
synth_square,
synth_sawtooth,
synth_triangle,
synth_trapezium,
synth_trapetz = synth_trapezium, /* Deprecated name for trapezium */
synth_exp,
/* Tones above, noises below */
synth_whitenoise,
synth_noise = synth_whitenoise, /* Just a handy alias */
synth_tpdfnoise,
synth_pinknoise,
synth_brownnoise,
synth_pluck
} type_t;
static lsx_enum_item const synth_type[] = {
LSX_ENUM_ITEM(synth_, sine)
LSX_ENUM_ITEM(synth_, square)
LSX_ENUM_ITEM(synth_, sawtooth)
LSX_ENUM_ITEM(synth_, triangle)
LSX_ENUM_ITEM(synth_, trapezium)
LSX_ENUM_ITEM(synth_, trapetz)
LSX_ENUM_ITEM(synth_, exp)
LSX_ENUM_ITEM(synth_, whitenoise)
LSX_ENUM_ITEM(synth_, noise)
LSX_ENUM_ITEM(synth_, tpdfnoise)
LSX_ENUM_ITEM(synth_, pinknoise)
LSX_ENUM_ITEM(synth_, brownnoise)
LSX_ENUM_ITEM(synth_, pluck)
{0, 0}
};
typedef enum {synth_create, synth_mix, synth_amod, synth_fmod} combine_t;
static lsx_enum_item const combine_type[] = {
LSX_ENUM_ITEM(synth_, create)
LSX_ENUM_ITEM(synth_, mix)
LSX_ENUM_ITEM(synth_, amod)
LSX_ENUM_ITEM(synth_, fmod)
{0, 0}
};
/******************************************************************************
* start of pink noise generator stuff
* algorithm stolen from:
* Author: Phil Burk, http://www.softsynth.com
*/
#define PINK_MAX_RANDOM_ROWS (30)
#define PINK_RANDOM_BITS (24)
#define PINK_RANDOM_SHIFT ((sizeof(int32_t)*8)-PINK_RANDOM_BITS)
typedef struct {
long pink_Rows[PINK_MAX_RANDOM_ROWS];
long pink_RunningSum; /* Used to optimize summing of generators. */
int pink_Index; /* Incremented each sample. */
int pink_IndexMask; /* Index wrapped by ANDing with this mask. */
float pink_Scalar; /* Used to scale within range of -1 to +1 */
} PinkNoise;
/* Setup PinkNoise structure for N rows of generators. */
static void InitializePinkNoise(PinkNoise * pink, size_t numRows)
{
size_t i;
long pmax;
pink->pink_Index = 0;
pink->pink_IndexMask = (1 << numRows) - 1;
/* Calculate maximum possible signed random value. Extra 1 for white noise always added. */
pmax = (numRows + 1) * (1 << (PINK_RANDOM_BITS - 1));
pink->pink_Scalar = 1.0f / pmax;
/* Initialize rows. */
for (i = 0; i < numRows; i++)
pink->pink_Rows[i] = 0;
pink->pink_RunningSum = 0;
}
/* Generate Pink noise values between -1 and +1 */
static float GeneratePinkNoise(PinkNoise * pink)
{
long newRandom;
long sum;
float output;
/* Increment and mask index. */
pink->pink_Index = (pink->pink_Index + 1) & pink->pink_IndexMask;
/* If index is zero, don't update any random values. */
if (pink->pink_Index != 0) {
/* Determine how many trailing zeros in PinkIndex. */
/* This algorithm will hang if n==0 so test first. */
int numZeros = 0;
int n = pink->pink_Index;
while ((n & 1) == 0) {
n = n >> 1;
numZeros++;
}
/* Replace the indexed ROWS random value.
* Subtract and add back to RunningSum instead of adding all the random
* values together. Only one changes each time.
*/
pink->pink_RunningSum -= pink->pink_Rows[numZeros];
newRandom = RANQD1 >> PINK_RANDOM_SHIFT;
pink->pink_RunningSum += newRandom;
pink->pink_Rows[numZeros] = newRandom;
}
/* Add extra white noise value. */
newRandom = RANQD1 >> PINK_RANDOM_SHIFT;
sum = pink->pink_RunningSum + newRandom;
/* Scale to range of -1 to 0.9999. */
output = pink->pink_Scalar * sum;
return output;
}
/**************** end of pink noise stuff */
typedef enum {Linear, Square, Exp, Exp_cycle} sweep_t;
typedef struct {
/* options */
type_t type;
combine_t combine;
double freq, freq2, mult;
sweep_t sweep;
double offset, phase;
double p1, p2, p3; /* Use depends on synth type */
/* internal stuff */
double lp_last_out, hp_last_out, hp_last_in, ap_last_out, ap_last_in;
double cycle_start_time_s, c0, c1, c2, c3, c4;
PinkNoise pink_noise;
double * buffer;
size_t buffer_len, pos;
} channel_t;
/* Private data for the synthesizer */
typedef struct {
char * length_str;
channel_t * getopts_channels;
size_t getopts_nchannels;
size_t samples_done;
size_t samples_to_do;
channel_t * channels;
size_t number_of_channels;
sox_bool no_headroom;
double gain;
} priv_t;
static void create_channel(channel_t * chan)
{
memset(chan, 0, sizeof(*chan));
chan->freq2 = chan->freq = 440;
chan->p3 = chan->p2 = chan->p1 = -1;
}
static void set_default_parameters(channel_t * chan, size_t c)
{
switch (chan->type) {
case synth_square: /* p1 is pulse width */
if (chan->p1 < 0)
chan->p1 = 0.5; /* default to 50% duty cycle */
break;
case synth_triangle: /* p1 is position of maximum */
if (chan->p1 < 0)
chan->p1 = 0.5;
break;
case synth_trapezium:
/* p1 is length of rising slope,
* p2 position where falling slope begins
* p3 position of end of falling slope
*/
if (chan->p1 < 0) {
chan->p1 = 0.1;
chan->p2 = 0.5;
chan->p3 = 0.6;
} else if (chan->p2 < 0) { /* try a symmetric waveform */
if (chan->p1 <= 0.5) {
chan->p2 = (1 - 2 * chan->p1) / 2;
chan->p3 = chan->p2 + chan->p1;
} else {
/* symetric is not possible, fall back to asymmetrical triangle */
chan->p2 = chan->p1;
chan->p3 = 1;
}
} else if (chan->p3 < 0)
chan->p3 = 1; /* simple falling slope to the end */
break;
case synth_pinknoise:
/* Initialize pink noise signals with different numbers of rows. */
InitializePinkNoise(&(chan->pink_noise), 10 + 2 * c);
break;
case synth_exp:
if (chan->p1 < 0) /* p1 is position of maximum */
chan->p1 = 0.5;
if (chan->p2 < 0) /* p2 is amplitude */
chan->p2 = .5;
break;
case synth_pluck:
if (chan->p1 < 0)
chan->p1 = .4;
if (chan->p2 < 0)
chan->p2 = .2, chan->p3 = .9;
default: break;
}
}
#undef NUMERIC_PARAMETER
#define NUMERIC_PARAMETER(p, min, max) { \
char * end_ptr_np; \
double d_np = strtod(argv[argn], &end_ptr_np); \
if (end_ptr_np == argv[argn]) \
break; \
if (d_np < min || d_np > max || *end_ptr_np != '\0') { \
lsx_fail("parameter error"); \
return SOX_EOF; \
} \
chan->p = d_np / 100; /* adjust so abs(parameter) <= 1 */\
if (++argn == argc) \
break; \
}
static int getopts(sox_effect_t * effp, int argc, char **argv)
{
priv_t * p = (priv_t *) effp->priv;
channel_t master, * chan = &master;
int key = INT_MAX, argn = 0;
char dummy, * end_ptr;
const char *n;
--argc, ++argv;
if (argc && !strcmp(*argv, "-n")) p->no_headroom = sox_true, ++argv, --argc;
if (argc > 1 && !strcmp(*argv, "-j") && (
sscanf(argv[1], "%i %c", &key, &dummy) == 1 || (
(key = lsx_parse_note(argv[1], &end_ptr)) != INT_MAX &&
!*end_ptr))) {
argc -= 2;
argv += 2;
}
/* Get duration if given (if first arg starts with digit) */
if (argc && (isdigit((int)argv[argn][0]) || argv[argn][0] == '.')) {
p->length_str = lsx_malloc(strlen(argv[argn]) + 1);
strcpy(p->length_str, argv[argn]);
/* Do a dummy parse of to see if it will fail */
n = lsx_parsesamples(0., p->length_str, &p->samples_to_do, 't');
if (!n || *n)
return lsx_usage(effp);
argn++;
}
create_channel(chan);
if (argn < argc) { /* [off [ph [p1 [p2 [p3]]]]]] */
do { /* break-able block */
NUMERIC_PARAMETER(offset,-100, 100)
NUMERIC_PARAMETER(phase , 0, 100)
NUMERIC_PARAMETER(p1, 0, 100)
NUMERIC_PARAMETER(p2, 0, 100)
NUMERIC_PARAMETER(p3, 0, 100)
} while (0);
}
while (argn < argc) { /* type [combine] [f1[-f2] [off [ph [p1 [p2 [p3]]]]]] */
lsx_enum_item const * enum_p = lsx_find_enum_text(argv[argn], synth_type, lsx_find_enum_item_case_sensitive);
if (enum_p == NULL) {
lsx_fail("no type given");
return SOX_EOF;
}
p->getopts_channels = lsx_realloc(p->getopts_channels, sizeof(*p->getopts_channels) * (p->getopts_nchannels + 1));
chan = &p->getopts_channels[p->getopts_nchannels++];
memcpy(chan, &master, sizeof(*chan));
chan->type = enum_p->value;
if (++argn == argc)
break;
/* maybe there is a combine-type in next arg */
enum_p = lsx_find_enum_text(argv[argn], combine_type, lsx_find_enum_item_case_sensitive);
if (enum_p != NULL) {
chan->combine = enum_p->value;
if (++argn == argc)
break;
}
/* read frequencies if given */
if (!lsx_find_enum_text(argv[argn], synth_type, lsx_find_enum_item_case_sensitive) &&
argv[argn][0] != '-') {
static const char sweeps[] = ":+/-";
chan->freq2 = chan->freq = lsx_parse_frequency_k(argv[argn], &end_ptr, key);
if (chan->freq < (chan->type == synth_pluck? 27.5 : 0) ||
(chan->type == synth_pluck && chan->freq > 4220)) {
lsx_fail("invalid freq");
return SOX_EOF;
}
if (*end_ptr && strchr(sweeps, *end_ptr)) { /* freq2 given? */
if (chan->type >= synth_noise) {
lsx_fail("can't sweep this type");
return SOX_EOF;
}
chan->sweep = strchr(sweeps, *end_ptr) - sweeps;
chan->freq2 = lsx_parse_frequency_k(end_ptr + 1, &end_ptr, key);
if (chan->freq2 < 0) {
lsx_fail("invalid freq2");
return SOX_EOF;
}
if (p->length_str == NULL) {
lsx_fail("duration must be given when using freq2");
return SOX_EOF;
}
}
if (*end_ptr) {
lsx_fail("frequency: invalid trailing character");
return SOX_EOF;
}
if (chan->sweep >= Exp && chan->freq * chan->freq2 == 0) {
lsx_fail("invalid frequency for exponential sweep");
return SOX_EOF;
}
if (++argn == argc)
break;
}
/* read rest of parameters */
do { /* break-able block */
NUMERIC_PARAMETER(offset,-100, 100)
NUMERIC_PARAMETER(phase , 0, 100)
NUMERIC_PARAMETER(p1, 0, 100)
NUMERIC_PARAMETER(p2, 0, 100)
NUMERIC_PARAMETER(p3, 0, 100)
} while (0);
}
/* If no channel parameters were given, create one default channel: */
if (!p->getopts_nchannels) {
p->getopts_channels = lsx_malloc(sizeof(*p->getopts_channels));
memcpy(&p->getopts_channels[0], &master, sizeof(channel_t));
++p->getopts_nchannels;
}
if (!effp->in_signal.channels)
effp->in_signal.channels = p->getopts_nchannels;
return SOX_SUCCESS;
}
static int start(sox_effect_t * effp)
{
priv_t * p = (priv_t *)effp->priv;
size_t i, j, k;
p->samples_done = 0;
if (p->length_str)
if (lsx_parsesamples(effp->in_signal.rate, p->length_str, &p->samples_to_do, 't') == NULL)
return lsx_usage(effp);
p->number_of_channels = effp->in_signal.channels;
p->channels = lsx_calloc(p->number_of_channels, sizeof(*p->channels));
for (i = 0; i < p->number_of_channels; ++i) {
channel_t * chan = &p->channels[i];
*chan = p->getopts_channels[i % p->getopts_nchannels];
set_default_parameters(chan, i);
if (chan->type == synth_pluck) {
double min, max, frac, p2;
/* Low pass: */
double const decay_rate = -2; /* dB / s */
double const decay_f = min(912, 266 + 106 * log(chan->freq));
double d = sqr(dB_to_linear(decay_rate / chan->freq));
d = (d * cos(2 * M_PI * decay_f / effp->in_signal.rate) - 1) / (d - 1);
chan->c0 = d - sqrt(d * d - 1);
chan->c1 = 1 - chan->c0;
/* Single-pole low pass is very rate-dependent: */
if (effp->in_signal.rate < 44100 || effp->in_signal.rate > 48000) {
lsx_fail(
"sample rate for pluck must be 44100-48000; use `rate' to resample");
return SOX_EOF;
}
/* Decay: */
chan->c1 *= exp(-2e4/ (.05+chan->p1)/ chan->freq/ effp->in_signal.rate);
/* High pass (DC-block): */
chan->c2 = exp(-2 * M_PI * 10 / effp->in_signal.rate);
chan->c3 = (1 + chan->c2) * .5;
/* All pass (for fractional delay): */
d = chan->c0 / (chan->c0 + chan->c1);
chan->buffer_len = effp->in_signal.rate / chan->freq - d;
frac = effp->in_signal.rate / chan->freq - d - chan->buffer_len;
chan->c4 = (1 - frac) / (1 + frac);
chan->pos = 0;
/* Exitation: */
chan->buffer = lsx_calloc(chan->buffer_len, sizeof(*chan->buffer));
for (k = 0, p2 = chan->p2; k < 2 && p2 >= 0; ++k, p2 = chan->p3) {
double d1 = 0, d2, colour = pow(2., 4 * (p2 - 1));
int32_t r = p2 * 100 + .5;
for (j = 0; j < chan->buffer_len; ++j) {
do d2 = d1 + (chan->phase? DRANQD1:dranqd1(r)) * colour;
while (fabs(d2) > 1);
chan->buffer[j] += d2 * (1 - .3 * k);
d1 = d2 * (colour != 1);
#ifdef TEST_PLUCK
chan->buffer[j] = sin(2 * M_PI * j / chan->buffer_len);
#endif
}
}
/* In-delay filter graduation: */
for (j = 0, min = max = 0; j < chan->buffer_len; ++j) {
double d2, t = (double)j / chan->buffer_len;
chan->lp_last_out = d2 =
chan->buffer[j] * chan->c1 + chan->lp_last_out * chan->c0;
chan->ap_last_out =
d2 * chan->c4 + chan->ap_last_in - chan->ap_last_out * chan->c4;
chan->ap_last_in = d2;
chan->buffer[j] = chan->buffer[j] * (1 - t) + chan->ap_last_out * t;
min = min(min, chan->buffer[j]);
max = max(max, chan->buffer[j]);
}
/* Normalise: */
for (j = 0, d = 0; j < chan->buffer_len; ++j) {
chan->buffer[j] = (2 * chan->buffer[j] - max - min) / (max - min);
d += sqr(chan->buffer[j]);
}
lsx_debug("rms=%f c0=%f c1=%f df=%f d3f=%f c2=%f c3=%f c4=%f frac=%f",
10 * log(d / chan->buffer_len), chan->c0, chan->c1, decay_f,
log(chan->c0)/ -2 / M_PI * effp->in_signal.rate,
chan->c2, chan->c3, chan->c4, frac);
}
switch (chan->sweep) {
case Linear: chan->mult = p->samples_to_do?
(chan->freq2 - chan->freq) / p->samples_to_do / 2 : 0;
break;
case Square: chan->mult = p->samples_to_do?
sqrt(fabs(chan->freq2 - chan->freq)) / p->samples_to_do / sqrt(3.) : 0;
if (chan->freq > chan->freq2)
chan->mult = -chan->mult;
break;
case Exp: chan->mult = p->samples_to_do?
log(chan->freq2 / chan->freq) / p->samples_to_do * effp->in_signal.rate : 1;
chan->freq /= chan->mult;
break;
case Exp_cycle: chan->mult = p->samples_to_do?
(log(chan->freq2) - log(chan->freq)) / p->samples_to_do : 1;
break;
}
lsx_debug("type=%s, combine=%s, samples_to_do=%lu, f1=%g, f2=%g, "
"offset=%g, phase=%g, p1=%g, p2=%g, p3=%g mult=%g",
lsx_find_enum_value(chan->type, synth_type)->text,
lsx_find_enum_value(chan->combine, combine_type)->text,
(unsigned long)p->samples_to_do, chan->freq, chan->freq2,
chan->offset, chan->phase, chan->p1, chan->p2, chan->p3, chan->mult);
}
p->gain = 1;
effp->out_signal.mult = p->no_headroom? NULL : &p->gain;
return SOX_SUCCESS;
}
#define elapsed_time_s p->samples_done / effp->in_signal.rate
static int flow(sox_effect_t * effp, const sox_sample_t * ibuf, sox_sample_t * obuf,
size_t * isamp, size_t * osamp)
{
priv_t * p = (priv_t *) effp->priv;
unsigned len = min(*isamp, *osamp) / effp->in_signal.channels;
unsigned c, done;
int result = SOX_SUCCESS;
for (done = 0; done < len && result == SOX_SUCCESS; ++done) {
for (c = 0; c < effp->in_signal.channels; c++) {
sox_sample_t synth_input = *ibuf++;
channel_t * chan = &p->channels[c];
double synth_out; /* [-1, 1] */
if (chan->type < synth_noise) { /* Need to calculate phase: */
double phase; /* [0, 1) */
switch (chan->sweep) {
case Linear:
phase = (chan->freq + p->samples_done * chan->mult) *
elapsed_time_s;
break;
case Square:
phase = (chan->freq + sign(chan->mult) *
sqr(p->samples_done * chan->mult)) * elapsed_time_s;
break;
case Exp:
phase = chan->freq * exp(chan->mult * elapsed_time_s);
break;
case Exp_cycle: default: {
double f = chan->freq * exp(p->samples_done * chan->mult);
double cycle_elapsed_time_s = elapsed_time_s - chan->cycle_start_time_s;
if (f * cycle_elapsed_time_s >= 1) { /* move to next cycle */
chan->cycle_start_time_s += 1 / f;
cycle_elapsed_time_s = elapsed_time_s - chan->cycle_start_time_s;
}
phase = f * cycle_elapsed_time_s;
break;
}
}
phase = fmod(phase + chan->phase, 1.0);
switch (chan->type) {
case synth_sine:
synth_out = sin(2 * M_PI * phase);
break;
case synth_square:
/* |_______ | +1
* | | |
* |_______|__________| 0
* | | |
* | |__________| -1
* | |
* 0 p1 1
*/
synth_out = -1 + 2 * (phase < chan->p1);
break;
case synth_sawtooth:
/* | __| +1
* | __/ |
* |_______/_____| 0
* | __/ |
* |_/ | -1
* | |
* 0 1
*/
synth_out = -1 + 2 * phase;
break;
case synth_triangle:
/* | . | +1
* | / \ |
* |__/___\__| 0
* | / \ |
* |/ \| -1
* | |
* 0 p1 1
*/
if (phase < chan->p1)
synth_out = -1 + 2 * phase / chan->p1; /* In rising part of period */
else
synth_out = 1 - 2 * (phase - chan->p1) / (1 - chan->p1); /* In falling part */
break;
case synth_trapezium:
/* | ______ |+1
* | / \ |
* |__/________\___________| 0
* | / \ |
* |/ \_________|-1
* | |
* 0 p1 p2 p3 1
*/
if (phase < chan->p1) /* In rising part of period */
synth_out = -1 + 2 * phase / chan->p1;
else if (phase < chan->p2) /* In high part of period */
synth_out = 1;
else if (phase < chan->p3) /* In falling part */
synth_out = 1 - 2 * (phase - chan->p2) / (chan->p3 - chan->p2);
else /* In low part of period */
synth_out = -1;
break;
case synth_exp:
/* | | | +1
* | | | |
* | _| |_ | 0
* | __- -__ |
* |____--- ---____ | f(p2)
* | |
* 0 p1 1
*/
synth_out = dB_to_linear(chan->p2 * -200); /* 0 .. 1 */
if (phase < chan->p1)
synth_out = synth_out * exp(phase * log(1 / synth_out) / chan->p1);
else
synth_out = synth_out * exp((1 - phase) * log(1 / synth_out) / (1 - chan->p1));
synth_out = synth_out * 2 - 1; /* map 0 .. 1 to -1 .. +1 */
break;
default: synth_out = 0;
}
} else switch (chan->type) {
case synth_whitenoise:
synth_out = DRANQD1;
break;
case synth_tpdfnoise:
synth_out = .5 * (DRANQD1 + DRANQD1);
break;
case synth_pinknoise:
synth_out = GeneratePinkNoise(&(chan->pink_noise));
break;
case synth_brownnoise:
do synth_out = chan->lp_last_out + DRANQD1 * (1. / 16);
while (fabs(synth_out) > 1);
chan->lp_last_out = synth_out;
break;
case synth_pluck: {
double d = chan->buffer[chan->pos];
chan->hp_last_out =
(d - chan->hp_last_in) * chan->c3 + chan->hp_last_out * chan->c2;
chan->hp_last_in = d;
synth_out = range_limit(chan->hp_last_out, -1, 1);
chan->lp_last_out = d = d * chan->c1 + chan->lp_last_out * chan->c0;
chan->ap_last_out = chan->buffer[chan->pos] =
(d - chan->ap_last_out) * chan->c4 + chan->ap_last_in;
chan->ap_last_in = d;
chan->pos = chan->pos + 1 == chan->buffer_len? 0 : chan->pos + 1;
break;
}
default: synth_out = 0;
}
/* Add offset, but prevent clipping: */
synth_out = synth_out * (1 - fabs(chan->offset)) + chan->offset;
switch (chan->combine) {
case synth_create: synth_out *= SOX_SAMPLE_MAX; break;
case synth_mix : synth_out = (synth_out * SOX_SAMPLE_MAX + synth_input) * .5; break;
case synth_amod : synth_out = (synth_out + 1) * synth_input * .5; break;
case synth_fmod : synth_out *= synth_input; break;
}
*obuf++ = synth_out < 0? synth_out * p->gain - .5 : synth_out * p->gain + .5;
}
if (++p->samples_done == p->samples_to_do)
result = SOX_EOF;
}
*isamp = *osamp = done * effp->in_signal.channels;
return result;
}
static int stop(sox_effect_t * effp)
{
priv_t * p = (priv_t *) effp->priv;
size_t i;
for (i = 0; i < p->number_of_channels; ++i)
free(p->channels[i].buffer);
free(p->channels);
return SOX_SUCCESS;
}
static int lsx_kill(sox_effect_t * effp)
{
priv_t * p = (priv_t *) effp->priv;
free(p->getopts_channels);
free(p->length_str);
return SOX_SUCCESS;
}
const sox_effect_handler_t *lsx_synth_effect_fn(void)
{
static sox_effect_handler_t handler = {
"synth", "[-j KEY] [-n] [length [offset [phase [p1 [p2 [p3]]]]]]] {type [combine] [[%]freq[k][:|+|/|-[%]freq2[k]] [offset [phase [p1 [p2 [p3]]]]]]}",
SOX_EFF_MCHAN | SOX_EFF_LENGTH | SOX_EFF_GAIN,
getopts, start, flow, 0, stop, lsx_kill, sizeof(priv_t)
};
return &handler;
}