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
