| | Open Sound System |
| Do you have problems with sound/audio application development? Don't panic! Click here for help! |
Copyright (C) 4Front Technologies, 2002-2004. Released under GPLv2/CDDL.
This program was supposed to do a frequency sweep down from sample_rate/2 to 0 Hz. However due to some arithmetic problem the result was much more interesting.
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <soundcard.h>
char *dspname = "/dev/dsp";
int fd;
#define SIN_STEPS 48
static short sinebuf[48] = {
0, 4276, 8480, 12539, 16383, 19947, 23169, 25995,
28377, 30272, 31650, 32486, 32767, 32486, 31650, 30272,
28377, 25995, 23169, 19947, 16383, 12539, 8480, 4276,
0, -4276, -8480, -12539, -16383, -19947, -23169, -25995,
-28377, -30272, -31650, -32486, -32767, -32486, -31650, -30272,
-28377, -25995, -23169, -19947, -16383, -12539, -8480, -4276
};
#define F_SCALE (1000000)
int phase = 0, freq = F_SCALE / 2;
static void
sweeper (int speed, int channels, int fragsize)
{
short buf[4096], *p = buf;
int c, i, n, v, x;
fragsize /= 2 * channels;
speed /= 100;
for (i = 0; i < fragsize; i++)
{
x = (phase + F_SCALE / 2) / F_SCALE;
if (x < 0) x = 0;
v = sinebuf[x % SIN_STEPS] / 4;
phase = phase + freq * 480 / speed;
if (freq > 1000)
freq -= 3 * 480 / speed;
else
freq -= 1;
for (c = 0; c < channels; c++)
*p++ = v;
if (freq <= 0)
break;
}
write (fd, buf, i * 2 * channels);
}
int
main (int argc, char *argv[])
{
int bits, channels, speed, tmp;
int i, l;
if (argc == 2)
dspname = argv[1];
if ((fd = open (dspname, O_WRONLY, 0)) == -1)
{
perror (dspname);
exit (-1);
}
speed = 96000;
channels = 2;
bits = AFMT_S16_NE;
if (ioctl (fd, SNDCTL_DSP_CHANNELS, &channels) == -1)
{
perror ("SNDCTL_DSP_CHANNELS");
exit (-1);
}
if (ioctl (fd, SNDCTL_DSP_SETFMT, &bits) == -1)
{
perror ("SNDCTL_DSP_SETFMT");
exit (-1);
}
if (bits != AFMT_S16_NE)
{
fprintf (stderr,
"Device %s doesn't support 16 bit (native endian) format\n",
dspname);
exit (-1);
}
if (ioctl (fd, SNDCTL_DSP_SPEED, &speed) == -1)
{
perror ("SNDCTL_DSP_SPEED");
exit (-1);
}
if (ioctl (fd, SNDCTL_DSP_GETBLKSIZE, &tmp) == -1)
{
perror ("SNDCTL_DSP_GETBLKSIZE");
exit (-1);
}
printf ("Outputting sweep at %d Hz, %d channels, 16 bits\n", speed,
channels);
printf ("Fragment size is %d\n", tmp);
while (freq > 0)
sweeper (speed, channels, tmp);
exit (0);
}