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#define _GNU_SOURCE
#include <stdio.h>
#include <signal.h>
#include <complex.h>
#include <fftw3.h>
#include <alsa/asoundlib.h>
#define SAMPLE_RATE 8000
#define FFT_SIZE (1<<13)
static double *fft_in;
static fftw_complex *fft_out;
static fftw_plan fft_plan;
static int capturing = 1;
static void handle_signals(int signum __attribute__((unused)))
{
capturing = 0;
}
static int set_alsa_params(snd_pcm_t *pcm_handle)
{
snd_pcm_hw_params_t *hwparams;
unsigned int rate = SAMPLE_RATE;
snd_pcm_uframes_t bufsize = FFT_SIZE;
snd_pcm_hw_params_alloca(&hwparams);
if (snd_pcm_hw_params_any(pcm_handle, hwparams) < 0) {
fprintf(stderr, "Failed configuring device\n");
return -1;
}
if (snd_pcm_hw_params_set_access(pcm_handle, hwparams, SND_PCM_ACCESS_RW_INTERLEAVED) < 0) {
fprintf(stderr, "Failed setting access mode\n");
return -1;
}
if (snd_pcm_hw_params_set_format(pcm_handle, hwparams, SND_PCM_FORMAT_FLOAT64_LE) < 0) {
fprintf(stderr, "Failed setting format\n");
return -1;
}
if (snd_pcm_hw_params_set_rate_near(pcm_handle, hwparams, &rate, 0) < 0) {
fprintf(stderr, "Failed setting sample rate\n");
return -1;
}
if (snd_pcm_hw_params_set_buffer_size_near(pcm_handle, hwparams, &bufsize) < 0) {
fprintf(stderr, "Failed setting buffer size\n");
return -1;
}
if (snd_pcm_hw_params_set_channels(pcm_handle, hwparams, 1) < 0) {
fprintf(stderr, "Failed setting channel number\n");
return -1;
}
if (snd_pcm_hw_params(pcm_handle, hwparams) < 0) {
fprintf(stderr, "Failed applying hardware parameters\n");
return -1;
}
return 0;
}
static void fft_init()
{
fft_in = fftw_alloc_real(FFT_SIZE);
fft_out = fftw_alloc_complex(FFT_SIZE);
fft_plan = fftw_plan_dft_r2c_1d(FFT_SIZE, fft_in, fft_out, FFTW_ESTIMATE);
}
static void fft_cleanup()
{
fftw_destroy_plan(fft_plan);
fftw_free(fft_in);
fftw_free(fft_out);
}
static void process_frames()
{
int i, freq, index = -1;
double largest = -1;
fftw_execute(fft_plan);
/* find point with largest magnitude */
for (i=0; i<FFT_SIZE; i++) {
/* +1 because out[0] is DC result */
double a = cabs(fft_out[i+1]);
if (a > largest) {
largest = a;
index = i;
}
}
freq = index * SAMPLE_RATE / FFT_SIZE;
printf("freq: %d Hz\n", freq);
}
static void capture(snd_pcm_t *pcm_handle)
{
int read;
while(capturing) {
while ((read = snd_pcm_readi(pcm_handle, fft_in, FFT_SIZE)) < 0) {
snd_pcm_prepare(pcm_handle);
printf("overrun\n");
}
if (read == FFT_SIZE) {
process_frames();
}
}
}
int main()
{
snd_pcm_t *pcm_handle;
if (snd_pcm_open(&pcm_handle, "default", SND_PCM_STREAM_CAPTURE, 0) < 0) {
fprintf(stderr, "Failed opening device for capturing\n");
return 1;
}
if (set_alsa_params(pcm_handle) < 0) {
return 1;
}
signal(SIGINT, handle_signals);
signal(SIGTERM, handle_signals);
fft_init();
capture(pcm_handle);
snd_pcm_close(pcm_handle);
fft_cleanup();
return 0;
}
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