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/*
* Purpose: A simple program that does audio recording.
* Copyright (C) 4Front Technologies, 2002-2004. Released under GPLv2/CDDL.
*
* Description:
* This is a very minimal program that does audio recording. However to
* demonstrate processiong of audio data it computes the
* maximum value of the signal and displays a "LED" bars
* (using character mode console).
*/
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>
#include <soundcard.h>
int fd_in;
int sample_rate = 48000;
/*
* The open_audio_device opens the audio device and initializes it
* for the required mode. The same routine is used in the other
* simple sample programs too.
*/
static int
open_audio_device (char *name, int mode)
{
int tmp, fd;
if ((fd = open (name, mode, 0)) == -1)
{
perror (name);
exit (-1);
}
/*
* Setup the device. Note that it's important to set the
* sample format, number of channels and sample rate exactly in this order.
* Some devices depend on the order.
*/
/*
* Set the sample format
*/
tmp = AFMT_S16_NE; /* Native 16 bits */
if (ioctl (fd, SNDCTL_DSP_SETFMT, &tmp) == -1)
{
perror ("SNDCTL_DSP_SETFMT");
exit (-1);
}
if (tmp != AFMT_S16_NE)
{
fprintf (stderr,
"The device doesn't support the 16 bit sample format.\n");
exit (-1);
}
/*
* Set the number of channels (mono)
*/
tmp = 1;
if (ioctl (fd, SNDCTL_DSP_CHANNELS, &tmp) == -1)
{
perror ("SNDCTL_DSP_CHANNELS");
exit (-1);
}
if (tmp != 1)
{
fprintf (stderr, "The device doesn't support mono mode.\n");
exit (-1);
}
/*
* Set the sample rate
*/
sample_rate = 48000;
if (ioctl (fd, SNDCTL_DSP_SPEED, &sample_rate) == -1)
{
perror ("SNDCTL_DSP_SPEED");
exit (-1);
}
/*
* No need for error checking because we will automatically adjust the
* signal based on the actual sample rate. However most application must
* check the value of sample_rate and compare it to the requested rate.
*
* Small differences between the rates (10% or less) are normal and the
* applications should usually tolerate them. However larger differences may
* cause annoying pitch problems (Mickey Mouse).
*/
return fd;
}
void
process_input (void)
{
short buffer[1024];
int l, i, level;
/*
* First read a block of audio samples with proper error checking.
*/
if ((l = read (fd_in, buffer, sizeof (buffer))) == -1)
{
perror ("Audio read");
exit (-1); /* Or return an error code */
}
/*
* We are using 16 bit samples so the number of bytes returned by read must be
* converted to the number of samples (2 bytes per a 16 bit sample).
*
* Some care must be taken if this program is converted from 1 channels
* (mono) to 2 channels (stereo) or more.
*
* Handling more than 1 channels is bit more complicated because the channels
* are interleaved. This will be demonstrated in some other programs.
*/
l = l / 2;
/*
* After this point this routine will perform the peak volume computations.
* The {!code l} variable contains the number of samples in the buffer.
*
* The remaining lines can be removed and replaced with the required
* application code.
*/
level = 0;
for (i = 0; i < l; i++)
{
/*
* Take the next sample (i) and compute it's absolute value. Check if it
* was larger than the previous peak value.
*/
int v = buffer[i];
if (v < 0)
v = -v; /* abs */
if (v > level)
level = v;
}
/*
* Finally print the simple LED bar. The maximum value for a 16 bit
* sample is 32*1024-1. Convert this to 32 bars.
*
* This program uses linear scale for simplicity. Real world audio programs
* should probably use logarithmic scale (dB).
*/
level = (level + 1) / 1024;
for (i = 0; i < level; i++)
printf ("*");
for (i = level; i < 32; i++)
printf (".");
printf ("\r");
fflush (stdout);
}
int
main (int argc, char *argv[])
{
/*
* Use /dev/dsp as the default device because the system administrator
* may select the device using the {!xlink ossctl} program or some other
* methods
*/
char *name_in = "/dev/dsp";
/*
* It's recommended to provide some method for selecting some other
* device than the default. We use command line argument but in some cases
* an environment variable or some configuration file setting may be better.
*/
if (argc > 1)
name_in = argv[1];
/*
* It's mandatory to use O_RDONLY in programs that do only recording. Other
* modes may cause increased resource (memory) usage in the driver. It may
* also prevent other applications from using the same device for
* playback at the same time.
*/
fd_in = open_audio_device (name_in, O_RDONLY);
while (1)
process_input ();
exit (0);
}
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