Fundamentals/sinetone-optimized-bank/render.cpp

Using optimized neon functions

This sketch shows how to use the mathneon library which provides optimized implementation of many simple math functions. The code is based on the sinetone/render.cpp project, with the following differences:

• we include libraries/math_neon/math_neon.h instead of cmath
• we call sinf_neon() instead of sinf()
• we can therefore have many more oscillators than in the basic project (just about 90) and we are using them for a weird additive synth

/*
 ____  _____ _        _
| __ )| ____| |      / \
|  _ \|  _| | |     / _ \
| |_) | |___| |___ / ___ \
|____/|_____|_____/_/   \_\
http://bela.io
*/
#include <Bela.h>
#include <libraries/math_neon/math_neon.h>
#include <stdlib.h>
#include <time.h>


#define NUM_OSCS 40

float gPhaseIncrement;

float gFrequencies[NUM_OSCS];
float gPhases[NUM_OSCS];

float gFrequenciesLFO[NUM_OSCS];
float gPhasesLFO[NUM_OSCS];

float gScale;

bool setup(BelaContext *context, void *userData)
{
        gPhaseIncrement = 2.0 * M_PI * 1.0 / context->audioSampleRate;
        gScale = 1 / (float)NUM_OSCS * 0.5;

        srand (time(NULL));

        for(int k = 0; k < NUM_OSCS; ++k){
                        // Fill array gFrequencies[k] with random freq between 300 - 2700Hz
                        gFrequencies[k] = rand() / (float)RAND_MAX * 2400 + 300;
                        // Fill array gFrequenciesLFO[k] with random freq between 0.001 - 0.051Hz
                        gFrequenciesLFO[k] = rand() / (float)RAND_MAX * 0.05 + 0.001;
                        gPhasesLFO[k] = 0;
                }

        return true;
}

void render(BelaContext *context, void *userData)
{
        for(unsigned int n = 0; n < context->audioFrames; n++) {
                float out[2] = {0};

                for(int k = 0; k < NUM_OSCS; ++k){

                        // Calculate the LFO amplitude
                        float LFO = sinf_neon(gPhasesLFO[k]);
                        gPhasesLFO[k] += gFrequenciesLFO[k] * gPhaseIncrement;
                        if(gPhasesLFO[k] > M_PI)
                                gPhasesLFO[k] -= 2.0f * (float)M_PI;

                        // Calculate oscillator sinewaves and output them amplitude modulated
                        // by LFO sinewave squared.
                        // Outputs from the oscillators are summed in out[],
                        // with even numbered oscillators going to the left channel out[0]
                        // and odd numbered oscillators going to the right channel out[1]
                        out[k&1] += sinf_neon(gPhases[k]) * gScale * (LFO*LFO);
                        gPhases[k] += gFrequencies[k] * gPhaseIncrement;
                        if(gPhases[k] > M_PI)
                                gPhases[k] -= 2.0f * (float)M_PI;

                }
                audioWrite(context, n, 0, out[0]);
                audioWrite(context, n, 1, out[1]);
        }
}

void cleanup(BelaContext *context, void *userData)
{

}