Trill/square-sound/render.cpp

Trill Square oscillator pad

This example shows how to communicate with the Trill Square sensor using the Trill library. It sonifies the X-Y position and size of the touch via the control of an oscillator.

In this file Trill sensor is scanned in an AuxiliaryTask running in parallel with the audio thread and the horizontal and vertical position and size are stored in global variables.

The vertical position of the touch is mapped to frequency, while the horizontal position maps to left/right panning. Touch size is used to control the overal amplitude of the oscillator.

Changes in frequency, amplitude and panning are smoothed using LP filters to avoid artifacts.

/*
 ____  _____ _        _
| __ )| ____| |      / \
|  _ \|  _| | |     / _ \
| |_) | |___| |___ / ___ \
|____/|_____|_____/_/   \_\
http://bela.io
*/
#include <Bela.h>
#include <cmath>
#include <libraries/Trill/Trill.h>
#include <libraries/OnePole/OnePole.h>
#include <libraries/Oscillator/Oscillator.h>

// Trill object declaration
Trill touchSensor;

// Horizontal and vertical position for Trill sensor
float gTouchPosition[2] = { 0.0 , 0.0 };
// Touch size
float gTouchSize = 0.0;

// Oscillator object declaration
Oscillator osc;

// Range for oscillator frequency mapping
float gFreqRange[2] = { 200.0, 1500.0 };

// One Pole filters objects declaration
OnePole freqFilt, panFilt, ampFilt;

// Default panning values for the sinewave
float gAmpL = 1.0;
float gAmpR = 1.0;

// Sleep time for auxiliary task
unsigned int gTaskSleepTime = 12000; // microseconds

/*
 * Function to be run on an auxiliary task that reads data from the Trill sensor.
 * Here, a loop is defined so that the task runs recurrently for as long as the
 * audio thread is running.
 */
void loop(void*)
{
        while(!Bela_stopRequested())
        {
                // Read locations from Trill sensor
                touchSensor.readI2C();
                gTouchSize = touchSensor.compoundTouchSize();
                gTouchPosition[0] = touchSensor.compoundTouchHorizontalLocation();
                gTouchPosition[1] = touchSensor.compoundTouchLocation();
                usleep(gTaskSleepTime);
        }
}

bool setup(BelaContext *context, void *userData)
{
        // Setup a Trill Square on i2c bus 1, using the default mode and address
        if(touchSensor.setup(1, Trill::SQUARE) != 0) {
                fprintf(stderr, "Unable to initialise Trill Square\n");
                return false;
        }

        touchSensor.printDetails();

        // Set and schedule auxiliary task for reading sensor data from the I2C bus
        Bela_runAuxiliaryTask(loop);

        // Setup low pass filters for smoothing frequency, amplitude and panning
        freqFilt.setup(1, context->audioSampleRate); // Cut-off frequency = 1Hz
        panFilt.setup(1, context->audioSampleRate); // Cut-off frequency = 1Hz
        ampFilt.setup(1, context->audioSampleRate); // Cut-off frequency = 1Hz

        // Setup triangle oscillator
        osc.setup(context->audioSampleRate, Oscillator::triangle);

        return true;
}

void render(BelaContext *context, void *userData)
{
        for(unsigned int n = 0; n < context->audioFrames; n++) {

                float frequency;
                // Map Y-axis to a frequency range
                frequency = map(gTouchPosition[1], 0, 1, gFreqRange[0], gFreqRange[1]);
                // Smooth frequency using low-pass filter
                frequency = freqFilt.process(frequency);

                // Smooth panning (given by the X-axis) changes using low-pass filter
                float panning = panFilt.process(gTouchPosition[0]);
                // Calculate amplitude of left and right channels
                gAmpL = 1 - panning;
                gAmpR = panning;

                // Smooth changes in the amplitude of the oscillator (given by touch
                // size) using a low-pass filter
                float amplitude = ampFilt.process(gTouchSize);
                // Calculate output of the oscillator
                float out = amplitude * osc.process(frequency);

                // Write oscillator to left and right channels
                for(unsigned int channel = 0; channel < context->audioOutChannels; channel++) {
                        if(channel == 0) {
                                audioWrite(context, n, channel, gAmpL*out);
                        } else if (channel == 1) {
                                audioWrite(context, n, channel, gAmpR*out);
                        }
                }
        }
}

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