Fundamentals/sinetone/render.cpp

Producing your first bleep!

This sketch is the hello world of embedded interactive audio. Better known as bleep, it produces a sine tone.

The frequency of the sine tone is determined by a global variable, gFrequency. The sine tone is produced by incrementing the phase of a sin function on every audio frame.

In render() you'll see a nested for loop structure. You'll see this in all Bela projects. The first for loop cycles through 'audioFrames', the second through 'audioChannels' (in this case left 0 and right 1). It is good to familiarise yourself with this structure as it's fundamental to producing sound with the system.

/*
 ____  _____ _        _
| __ )| ____| |      / \
|  _ \|  _| | |     / _ \
| |_) | |___| |___ / ___ \
|____/|_____|_____/_/   \_\
http://bela.io
*/
 
#include <Bela.h>
#include <cmath>
 
float gFrequency = 440.0;
float gPhase;
float gInverseSampleRate;
 
bool setup(BelaContext *context, void *userData)
{
        gInverseSampleRate = 1.0 / context->audioSampleRate;
        gPhase = 0.0;
 
        return true;
}
 
void render(BelaContext *context, void *userData)
{
        for(unsigned int n = 0; n < context->audioFrames; n++) {
                float out = 0.8f * sinf(gPhase);
                gPhase += 2.0f * (float)M_PI * gFrequency * gInverseSampleRate;
                if(gPhase > M_PI)
                        gPhase -= 2.0f * (float)M_PI;
 
                for(unsigned int channel = 0; channel < context->audioOutChannels; channel++) {
                        audioWrite(context, n, channel, out);
                }
        }
}
 
void cleanup(BelaContext *context, void *userData)
{
 
}