parrot.c

/*
 * EXAMPLE CODE. Found on ORLY Website.
 *
 * parrot.c
 * Program to illustrate /dev/dsp device
 * Records several seconds of sound, then echoes it back.
 * Runs until Control-C is pressed.
 
    EXTRA CHALLENGES!!
    
# Make the parameters selectable using command-line options (sample rate, size, time). See the effect on sound quality with different sampling rates.

# Reverse the sound samples (and listen for hidden messages), or play them back at a different sampling rate from the one at which they were recorded.

# Automatically start recording when the voice starts and stop when silence occurs (or a maximum time is reached). Hints: for 8-bit unsigned data the zero value is 0x80, but you will likely see values that vary around this level due to noise. Set a noise threshold (or better yet, measure the background noise level at the start of the program).

# Bonus question: modify the program so that it can recognize the words that are spoken. 
 
 */

#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/ioctl.h>
#include <stdlib.h>
#include <stdio.h>
#include <linux/soundcard.h>

#define LENGTH 3    /* how many seconds of speech to store */
#define RATE 8000   /* the sampling rate */
#define SIZE 8      /* sample size: 8 or 16 bits */
#define CHANNELS 1  /* 1 = mono 2 = stereo */

/* this buffer holds the digitized audio */
unsigned char buf[LENGTH*RATE*SIZE*CHANNELS/8];

int main()
{
    int fd;	/* sound device file descriptor */
    int arg;	/* argument for ioctl calls */
    int status;   /* return status of system calls */

    /* open sound device */
    fd = open("/dev/dsp", O_RDWR);
    if (fd < 0) {
        perror("open of /dev/dsp failed");
        exit(1);
    }

    /* set sampling parameters */
    arg = SIZE;	   /* sample size */
    status = ioctl(fd, SOUND_PCM_WRITE_BITS, &arg);
    if (status == -1)
        perror("SOUND_PCM_WRITE_BITS ioctl failed");
    if (arg != SIZE)
        perror("unable to set sample size");

    arg = CHANNELS;  /* mono or stereo */
    status = ioctl(fd, SOUND_PCM_WRITE_CHANNELS, &arg);
    if (status == -1)
        perror("SOUND_PCM_WRITE_CHANNELS ioctl failed");
    if (arg != CHANNELS)
        perror("unable to set number of channels");

    arg = RATE;	   /* sampling rate */
    status = ioctl(fd, SOUND_PCM_WRITE_RATE, &arg);
    if (status == -1)
        perror("SOUND_PCM_WRITE_WRITE ioctl failed");

    while (1) { /* loop until Control-C */
        printf("Say something:\n");
        status = read(fd, buf, sizeof(buf)); /* record some sound */
        if (status != sizeof(buf))
            perror("read wrong number of bytes");
        printf("You said:\n");
        status = write(fd, buf, sizeof(buf)); /* play it back */
        if (status != sizeof(buf))
            perror("wrote wrong number of bytes");
        /* wait for playback to complete before recording again */
        status = ioctl(fd, SOUND_PCM_SYNC, 0); 
        if (status == -1)
            perror("SOUND_PCM_SYNC ioctl failed");
    }
}