C++ - Play back a tone generated from a sinusoidal wave

Question

Hey everyone, I'm currently trying to figure out how to play back a tone I have generated using a sinusoidal wave.

Here's my code:

#include <iostream>
#include <OpenAL/al.h>
#include <OpenAL/alc.h>
#include <Math.h>

using namespace std;

int main (int argc, char * const argv[]) {

    int number = 0;
    int i, size;
    double const Pi=4*atan(1); 
    cout << "Enter number of seconds:" << endl;
    scanf("%d", &number);
    size = 44100*number;
    unsigned char buffer [size]; //buffer array

    for(i = 0; i < size; i++){
        buffer[i] = (char)sin((2*Pi*440)/(44100*i))*127;
    }

    return 0;
}

Obviously it doesn't do anything at the moment, since I have no idea how to play the buffer. I don't want to generate a wav file, nor do I want to load one in. I just want to play back the buffer I have generated.

I am currently working on Mac OS X, and have tried using OpenAL methods - however I have found that alut and alu are not part of it anymore and if I try to use it then it turns out that it's all depredated anyway. I have also tried to include QAudioOutput, but for some reason it does not appear to be anywhere on my Mac.

I just want a simple playback of the tone I've created. Does anyone have anything they can point me to?

Thanks heaps!!!

Answer 1

I've written an example exactly for this. Runs fine with OpenAL under MacOSX and plays smooth sines. Take a look here: http://ioctl.eu/blog/2011/03/16/openal-sine-synth/

Code is quite short, i guess i can add it here as well for sake of completeness:

#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <iostream>
#include <OpenAL/al.h>
#include <OpenAL/alc.h>

#define CASE_RETURN(err) case (err): return "##err"
const char* al_err_str(ALenum err) {
    switch(err) {
        CASE_RETURN(AL_NO_ERROR);
        CASE_RETURN(AL_INVALID_NAME);
        CASE_RETURN(AL_INVALID_ENUM);
        CASE_RETURN(AL_INVALID_VALUE);
        CASE_RETURN(AL_INVALID_OPERATION);
        CASE_RETURN(AL_OUT_OF_MEMORY);
    }
    return "unknown";
}
#undef CASE_RETURN

#define __al_check_error(file,line) \
    do { \
        ALenum err = alGetError(); \
        for(; err!=AL_NO_ERROR; err=alGetError()) { \
            std::cerr << "AL Error " << al_err_str(err) << " at " << file << ":" << line << std::endl; \
        } \
    }while(0)

#define al_check_error() \
    __al_check_error(__FILE__, __LINE__)


void init_al() {
    ALCdevice *dev = NULL;
    ALCcontext *ctx = NULL;

    const char *defname = alcGetString(NULL, ALC_DEFAULT_DEVICE_SPECIFIER);
    std::cout << "Default device: " << defname << std::endl;

    dev = alcOpenDevice(defname);
    ctx = alcCreateContext(dev, NULL);
    alcMakeContextCurrent(ctx);
}

void exit_al() {
    ALCdevice *dev = NULL;
    ALCcontext *ctx = NULL;
    ctx = alcGetCurrentContext();
    dev = alcGetContextsDevice(ctx);

    alcMakeContextCurrent(NULL);
    alcDestroyContext(ctx);
    alcCloseDevice(dev);
}

int main(int argc, char* argv[]) {
    /* initialize OpenAL */
    init_al();

    /* Create buffer to store samples */
    ALuint buf;
    alGenBuffers(1, &buf);
    al_check_error();

    /* Fill buffer with Sine-Wave */
    float freq = 440.f;
    int seconds = 4;
    unsigned sample_rate = 22050;
    size_t buf_size = seconds * sample_rate;

    short *samples;
    samples = new short[buf_size];
    for(int i=0; i<buf_size; ++i) {
        samples[i] = 32760 * sin( (2.f*float(M_PI)*freq)/sample_rate * i );
    }

    /* Download buffer to OpenAL */
    alBufferData(buf, AL_FORMAT_MONO16, samples, buf_size, sample_rate);
    al_check_error();


    /* Set-up sound source and play buffer */
    ALuint src = 0;
    alGenSources(1, &src);
    alSourcei(src, AL_BUFFER, buf);
    alSourcePlay(src);

    /* While sound is playing, sleep */
    al_check_error();
    sleep(seconds);

    /* Dealloc OpenAL */
    exit_al();
    al_check_error();
    return 0;
}

Update: I've found OpenAL a bit too limiting for my needs, like I have some problems with low-latency playback as this appears to be not the primary domain of OpenAL. Instead, I've found the very convincing PortAudio: http://www.portaudio.com/ It supports all major platforms (Mac,Win,Unix/ALSA) and looks very good. There is an example for sine playback which is far more sophisticated, yet quite simple. Just download the latest release and find the sine-playback sample at test/patest_sine.c

Answer 2

You will need to go through the OS to play back sounds. It's not as straightforward as you would think. In OSX, you will need to go through CoreAudio.

A better approach would be to use a wrapper library like PortAudio (http://www.portaudio.com/) which will make your code more portable and save you some of the boilerplate needed to get sound out of your program.

Answer 3

Try this (this program uses Z transform concept, a complete example that generates dtmf tones using ALSA and compilable on LINUX are available here)‌‌‌‌‌‌‌‌‌‌‌‌‌‌‌‌‌‌‌‌‌‌‌‌‌:

/*
 *  Cosine Samples Generator
 *
 *  Autor: Volnei Klehm
 *  Data: 04/01/2014
 */

#include <math.h>
#include <stdio.h>

#define S_FREQ 8000 /*Sample frequency, should be greater thar 2*sineFrequency
          If using audio output it has to be the same saple frequency 
          Used there*/

const float frequency_in_Hertz = 697; /*set output frequency*/
const float generatorContant1 = cosf(2*M_PI*(frequency_in_Hertz/S_FREQ));
const float generatorContant2 = sinf(2*M_PI*(frequency_in_Hertz/S_FREQ));


float GenerateSignal(){
  static float Register[2]={1,0};
  static float FeedBack;

  FeedBack=2*generatorContant1*Register[0]-Register[1];
  Register[1]=Register[0];  
  Register[0]=FeedBack;

  return (generatorContant2*Register[1]);
}


int main(void) {
  /*generate 300 samples*/
  for (int NumberOfSamples = 300; NumberOfSamples > 0; NumberOfSamples--) 
    printf("\n%f", GenerateSignal());
  return 0;
}