ft8_lib/gen_ft8.cpp

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#include <cstdlib>
#include <cstring>
#include <cstdio>
#include <cmath>
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#include "common/wave.h"
#include "common/debug.h"
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//#include "ft8/v1/pack.h"
//#include "ft8/v1/encode.h"
#include "ft8/pack.h"
#include "ft8/encode.h"
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#include "ft8/constants.h"
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#define LOG_LEVEL LOG_INFO
void gfsk_pulse(int n_spsym, float b, float *pulse) {
const float c = M_PI * sqrtf(2 / logf(2));
for (int i = 0; i < 3*n_spsym; ++i) {
float t = i/(float)n_spsym - 1.5f;
pulse[i] = (erff(c * b * (t + 0.5f)) - erff(c * b * (t - 0.5f))) / 2;
}
}
// Same as synth_fsk, but uses GFSK phase shaping
void synth_gfsk(const uint8_t *symbols, int n_sym, float f0, int n_spsym, int signal_rate, float *signal)
{
LOG(LOG_DEBUG, "n_spsym = %d\n", n_spsym);
int n_wave = n_sym * n_spsym;
float hmod = 1.0f;
// Compute the smoothed frequency waveform.
// Length = (nsym+2)*nsps samples, first and last symbols extended
float dphi_peak = 2 * M_PI * hmod / n_spsym;
float dphi[n_wave + 2*n_spsym];
// Shift frequency up by f0
for (int i = 0; i < n_wave + 2*n_spsym; ++i) {
dphi[i] = 2 * M_PI * f0 / signal_rate;
}
float pulse[3 * n_spsym];
gfsk_pulse(n_spsym, 2.0f, pulse);
for (int i = 0; i < n_sym; ++i) {
int ib = i * n_spsym;
for (int j = 0; j < 3*n_spsym; ++j) {
dphi[j + ib] += dphi_peak*symbols[i]*pulse[j];
}
}
// Add dummy symbols at beginning and end with tone values equal to 1st and last symbol, respectively
for (int j = 0; j < 2*n_spsym; ++j) {
dphi[j] += dphi_peak*pulse[j + n_spsym]*symbols[0];
dphi[j + n_sym * n_spsym] += dphi_peak*pulse[j]*symbols[n_sym - 1];
}
// Calculate and insert the audio waveform
float phi = 0;
for (int k = 0; k < n_wave; ++k) { // Don't include dummy symbols
signal[k] = sinf(phi);
phi = fmodf(phi + dphi[k + n_spsym], 2*M_PI);
}
// Apply envelope shaping to the first and last symbols
int n_ramp = n_spsym / 8;
for (int i = 0; i < n_ramp; ++i) {
float env = (1 - cosf(2 * M_PI * i / (2 * n_ramp))) / 2;
signal[i] *= env;
signal[n_wave - 1 - i] *= env;
}
}
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// Convert a sequence of symbols (tones) into a sinewave of continuous phase (FSK).
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// Symbol 0 gets encoded as a sine of frequency f0, the others are spaced in increasing
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// fashion.
void synth_fsk(const uint8_t *symbols, int num_symbols, float f0, float spacing,
float symbol_rate, float signal_rate, float *signal) {
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float phase = 0;
float dt = 1/signal_rate;
float dt_sym = 1/symbol_rate;
float t = 0;
int j = 0;
int i = 0;
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while (j < num_symbols) {
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float f = f0 + symbols[j] * spacing;
phase = fmodf(phase + 2 * M_PI * f / signal_rate, 2 * M_PI);
signal[i] = sinf(phase);
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t += dt;
if (t >= dt_sym) {
// Move to the next symbol
t -= dt_sym;
++j;
}
++i;
}
}
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void usage() {
printf("Generate a 15-second WAV file encoding a given message.\n");
printf("Usage:\n");
printf("\n");
printf("gen_ft8 MESSAGE WAV_FILE [FREQUENCY]\n");
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printf("\n");
printf("(Note that you might have to enclose your message in quote marks if it contains spaces)\n");
}
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int main(int argc, char **argv) {
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// Expect two command-line arguments
if (argc < 3) {
usage();
return -1;
}
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const char *message = argv[1];
const char *wav_path = argv[2];
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float frequency = 1000.0;
if (argc > 3) {
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frequency = atof(argv[3]);
}
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// First, pack the text data into binary message
uint8_t packed[ft8::K_BYTES];
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//int rc = packmsg(message, packed);
int rc = ft8::pack77(message, packed);
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if (rc < 0) {
printf("Cannot parse message!\n");
printf("RC = %d\n", rc);
return -2;
}
printf("Packed data: ");
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for (int j = 0; j < 10; ++j) {
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printf("%02x ", packed[j]);
}
printf("\n");
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// Second, encode the binary message as a sequence of FSK tones
uint8_t tones[ft8::NN]; // FT8_NN = 79, lack of better name at the moment
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//genft8(packed, 0, tones);
ft8::genft8(packed, tones);
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printf("FSK tones: ");
for (int j = 0; j < ft8::NN; ++j) {
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printf("%d", tones[j]);
}
printf("\n");
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// Third, convert the FSK tones into an audio signal
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const int sample_rate = 12000;
const float symbol_rate = 6.25f;
const int num_samples = (int)(0.5f + ft8::NN / symbol_rate * sample_rate);
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const int num_silence = (15 * sample_rate - num_samples) / 2;
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float signal[num_silence + num_samples + num_silence];
for (int i = 0; i < num_silence + num_samples + num_silence; i++) {
signal[i] = 0;
}
// synth_fsk(tones, ft8::NN, frequency, symbol_rate, symbol_rate, sample_rate, signal + num_silence);
synth_gfsk(tones, ft8::NN, frequency, sample_rate / symbol_rate, sample_rate, signal + num_silence);
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save_wav(signal, num_silence + num_samples + num_silence, sample_rate, wav_path);
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return 0;
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}