Audio/envelope-generator/render.cpp

ADSR envelope generator

This sketch demonstrates how to make a simple oscillator with different waveforms and how to use the ADSR library to apply an envelope to an audio signal.

The ADSR gate is controlled by a button connected to digital pin 0. When the button is pressed the gate is turned ON and when it is released the gate is turned OFF.

The oscillator has 4 different waveforms available: sinewave, square wave, triangle wave and sawtooth. A button connected to digital pin 1. When the button is pressed the waveform of the oscillator changes. Continuous presses of the button will cycle over the different waveforms.

The frequency of the oscillator and the parameters of the ADSR are fixed to some predefined values in global variables. You can explore how to change these at runtime.

To learn more about ADSRs and how to use the ADSR library, make sure to check Nigel Redmon's fantastic blog: https://www.earlevel.com/main/category/envelope-generators/

/*
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| __ )| ____| |      / \
|  _ \|  _| | |     / _ \
| |_) | |___| |___ / ___ \
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http://bela.io
*/
 
#include <Bela.h>
#include <cmath>
#include <libraries/ADSR/ADSR.h>
 
ADSR envelope; // ADSR envelope
 
float gAttack = 0.1; // Envelope attack (seconds)
float gDecay = 0.25; // Envelope decay (seconds)
float gRelease = 0.5; // Envelope release (seconds)
float gSustain = 1.0; // Envelope sustain level
 
float gFrequency = 320.0; // Oscillator frequency (Hz)
float gPhase; // Oscillator phase
float gInverseSampleRate;
 
// Oscillator type
enum osc_type
{
        sine,           // 0
        triangle,       // 1
        square,         // 2
        sawtooth,       // 3
        numOscTypes
};
 
unsigned int gOscType = 0; // Selected oscillator type
float gAmplitude = 0.3f; // Amplitude scaling for oscillator's envelope
 
int gTriggerButtonPin = 0; // Digital pin to which gate button should be connected
int gTriggerButtonLastStatus = 0; // Last status of gate button
 
int gModeButtonPin = 1; // Digital pin to which oscillator selection button should be connected
int gModeButtonLastStatus = 0; // Last status of oscillator selection button
 
bool setup(BelaContext *context, void *userData)
{
        gInverseSampleRate = 1.0 / context->audioSampleRate;
        gPhase = 0.0;
 
        // Set ADSR parameters
        envelope.setAttackRate(gAttack * context->audioSampleRate);
        envelope.setDecayRate(gDecay * context->audioSampleRate);
        envelope.setReleaseRate(gRelease * context->audioSampleRate);
        envelope.setSustainLevel(gSustain);
 
        // Set buttons pins as inputs
        pinMode(context, 0, gTriggerButtonPin, INPUT);
        pinMode(context, 0, gModeButtonPin, INPUT);
 
        return true;
}
 
void render(BelaContext *context, void *userData)
{
 
        for(unsigned int n = 0; n < context->audioFrames; n++) {
 
                // Read status of gate button
                int triggerButtonStatus = digitalRead(context, n, gTriggerButtonPin);
 
                // If gate button has been pressed...
                if(triggerButtonStatus && !gTriggerButtonLastStatus) {
                        // ...turn ON the envelope's gate
                        envelope.gate(true);
                        rt_printf("Gate on\n");
                // If button has been depressed...
                } else if (!triggerButtonStatus && gTriggerButtonLastStatus) {
                        // ...turn OFF the envelope's gate
                        envelope.gate(false);
                        rt_printf("Gate off\n");
                }
                // Store last status
                gTriggerButtonLastStatus = triggerButtonStatus;
 
                // Read status of oscillator mode selector button
                int modeButtonStatus = digitalRead(context, 0, gModeButtonPin);
 
                // If button has been pressed...
                if(modeButtonStatus && !gModeButtonLastStatus) {
                        // Change oscillator type
                        gOscType += 1;
                        // Wrap around number of different oscillator types if counter is out of bounds
                        if(gOscType >= numOscTypes)
                                gOscType = 0;
                        rt_printf("Oscillator type: %d\n", gOscType);
                }
                // Store last status
                gModeButtonLastStatus = modeButtonStatus;
 
                float amp = gAmplitude * envelope.process();
 
                // Calculate output based on the selected oscillator mode
                float out;
                switch(gOscType) {
                        default:
                        // SINEWAVE
                        case sine:
                                out = sinf(gPhase);
                                break;
                        // TRIANGLE WAVE
                        case triangle:
                                if (gPhase > 0) {
                                      out = -1 + (2 * gPhase / (float)M_PI);
                                } else {
                                      out = -1 - (2 * gPhase/ (float)M_PI);
                                }
                                break;
                        // SQUARE WAVE
                        case square:
                                if (gPhase > 0) {
                                      out = 1;
                                } else {
                                      out = -1;
                                }
                                break;
                        // SAWTOOTH
                        case sawtooth:
                                out = 1 - (1 / (float)M_PI * gPhase);
                                break;
                }
                out = amp * out;
 
                // Compute phase
                gPhase += 2.0f * (float)M_PI * gFrequency * gInverseSampleRate;
                if(gPhase > M_PI)
                        gPhase -= 2.0f * (float)M_PI;
 
                // Write output to different channels
                for(unsigned int channel = 0; channel < context->audioOutChannels; channel++) {
                        audioWrite(context, n, channel, out);
                }
        }
}
 
void cleanup(BelaContext *context, void *userData)
{
}