OpenAL - Test #1

Well, it wasn't in my plans to to this this evening... This test wasn't planned at all :D But since I had headache this evening, I didn't feel the right mood for studying :P
So, I got disconnected from the IM client (all of them), took a tutorial and the reference of OpenAL and I tried to make a sound.

The reason is simple: in these days I'm getting into nerdcore music (notabily, 8 Bit Weapon :D So I absolutely wanted to create my own 8-bit sound (and, you know, once you get the sound you want, you did the most).

So, OpenAL was my way.

I'm not an audio expert, I really find sampling, frequencies and so on difficult to get (well, actually it isn't at all :D It's only that I found a bit difficult to build a PCM sine wave from nothing. Then I found out that my problem is only that "buffer frequency" was the "sampling frequency", not the "frequency of my signal" (obviusly)).

So, this is my test. Quite short for 2 hours of works! (or more). Well, it was my first time :D Now I got it, so next works should be more easy.

#if 0
#!/bin/sh

FILE=`basename $0 | sed "s/\.[Cc].*$//"`
EXT=` basename $0 | sed "s/^.*\.\([Cc].*\)$/\1/"`

CC="gcc -g -Wall -Wextra -pedantic -std=c99"

$CC $FILE.$EXT -o $FILE -lm -lopenal -lalut

exit
#endif

#include 
#include 

#include 

#define D2R 0.0174532925

#include 
#include 

#include 

int main(int argc, char **argv)
{
 // Initialize a context
 alutInit(&argc, argv);
 // Clean error flags
 alGetError();

 // Allocate buffers
 ALuint buffer[1];

 // Create the buffers
 alGenBuffers(1, buffer);
 if (alGetError() != AL_NO_ERROR)
  return -1;

 // Build the data
 ALenum format = AL_FORMAT_MONO8;
 ALsizei size;
 ALsizei freq;
 ALboolean loop;
 ALvoid *data;

 char file[512];
 printf("Please insert a path for the file to play (space for none), enter to confirm\n");
 fgets(file, 512, stdin);
 if (file[0] < ' ') // The first char is not a string valid char (i.e. empty string)
  // Load from extern file
  alutLoadWAVFile(file, &format, &data, &size, &freq, &loop);
 else {
  printf("Generating sine wave on user parameters\n");
  // Generate using math
  // We want a note of 440 Hz. 32 samples for each oscillation
  // for 1 seconds, means 440*32 bytes
  unsigned char *sineWave;
  int samples,
   frequency;
  printf("Which frequency? ");
  scanf("%d", &frequency);
  printf("How many samples for the wave? [try me between 2 and 16] ");
  scanf("%d", &samples);
  freq = samples * frequency;
  printf("We will use a sampling frequency equal to the signal frequency:\n"
    "sgnFreq * sgnSampl = %d * %d = %d\n", frequency, samples, freq);
  size = freq; // We don't need an higher frequency than the signal
  if (!(sineWave = malloc(size)))
   return -2;

  for (int i = 0; i < size; ++i) {
   float x = i * 360.0 / (float)samples;
   sineWave[i] = sin(x * D2R) * 128 + 128; // Clamp to [0,255]
  // printf("Sinewave[%d] = %d\n", i, sineWave[i]);
  }
  data = sineWave;
 }

 printf("Values: fmt: %d siz %d freq %d\n", format, size, freq);
 alBufferData(buffer[0], format, data, size, freq);

 // Setup sources
 ALuint source[1];
 alGenSources(1, source);
 if (alGetError() != AL_NO_ERROR)
  return -3;

 float srcPos[] = {3.0, 0.0, -3.0};

 alSourcei(source[0], AL_BUFFER, buffer[0]);
 alSourcefv(source[0], AL_POSITION, srcPos);

 float lstPos[] = {0.0, 0.0, 0.0};
 alListenerfv(AL_POSITION, lstPos);

 alSourcePlay(source[0]);

 // Wait until termination of the sound
 sleep(2);

 // Clear the things
 alDeleteSources(1, source);
 alDeleteBuffers(1, buffer);
 alutExit();

 return EXIT_SUCCESS;
}

The scope of this isn't really the use of openal (which is really simple), but the construction of a digital signal. In detail, you can actually understand how changing sampling frequency affect the riproduction of the signal.

Stay --sync