audioOscillator
Generate sine, square, and sawtooth waveforms
Description
The audioOscillator
System object™ generates tunable waveforms. Typical uses include the generation of test signals
for test benches, and the generation of control signals for audio effects. Properties of the
audioOscillator
System object specify the type of waveform generated.
To generate tunable waveforms:
Create the
audioOscillatorobject and set its properties.Call the object with arguments, as if it were a function.
To learn more about how System objects work, see What Are System Objects?
Creation
Syntax
Description
osc = audioOscillatorosc, with default property values.
osc = audioOscillator(signalTypeValue)signalTypeValue.
osc = audioOscillator(signalTypeValue,frequencyValue)frequencyValue.
osc = audioOscillator(___,
sets each property Name,Value)Name to the specified Value.
Unspecified properties have default values.
Example: osc =
audioOscillator('SignalType','sine','Frequency',8000,'DCOffset',1) creates a
System object, osc, which generates 8 kHz sinusoids with a DC offset of
one.
Properties
Usage
Syntax
Description
Output Arguments
Object Functions
To use an object function, specify the
System object as the first input argument. For
example, to release system resources of a System object named obj, use
this syntax:
release(obj)
The createAudioPluginClass and configureMIDI
functions map tunable properties of the audioOscillator
System object to user-facing parameters:
| Property | Range | Mapping | Units |
|---|---|---|---|
Frequency | [0.1, 20000] | log | Hz |
Amplitude | [0, 10] | linear | no units |
DCOffset | [–10, 10] | linear | no units |
DutyCycle (available when you set
SignalType to 'square') | [0, 1] | linear | no units |
Width (available when you set
SignalType to 'sawtooth') | [0, 1] | linear | no units |
Examples
Use the audioOscillator to generate a variable-frequency sine wave.
Create an audio oscillator to generate a sine wave. Use the default settings.
osc = audioOscillator;
Create a time scope to visualize the variable-frequency sine wave generated by the audio oscillator.
scope = timescope( ... 'SampleRate',osc.SampleRate, ... 'TimeSpanSource','Property','TimeSpan',0.1, ... 'YLimits',[-1.5,1.5], ... 'TimeSpanOverrunAction','Scroll', ... 'ShowGrid',true, ... 'Title','Variable-Frequency Sine Wave');
Place the audio oscillator in an audio stream loop. Increase the frequency of your sine wave in 50-Hz increments.
counter = 0; while (counter < 1e4) counter = counter + 1; sineWave = osc(); scope(sineWave); if mod(counter,1000)==0 osc.Frequency = osc.Frequency + 50; end end
Tune the frequency of an audio oscillator at regularly spaced intervals to create a melody. Play the melody to your audio output device.
Create a structure to hold the frequency values of notes in a melody.
notes = struct('C4',261.63,'E4',329.63,'G4sharp',415.30,'A4',440,'B4',493.88, ... 'C5',523.25,'D5',587.25,'D5sharp',622.25,'E5',659.25,'Silence',0);
Create audioOscillator and audioDeviceWriter objects. Use the default settings.
osc = audioOscillator; aDW = audioDeviceWriter;
Create a vector with the initial melody of Fur Elise.
melody = [notes.Silence notes.Silence,... notes.E5 notes.D5sharp notes.E5 notes.D5sharp notes.E5 notes.B4 ... notes.D5 notes.C5 notes.A4 notes.A4 notes.Silence ... notes.C4 notes.E4 notes.A4 notes.B4 notes.B4 notes.Silence ... notes.E4 notes.G4sharp notes.B4 notes.C5 notes.C5 notes.Silence];
Specify the note duration in seconds. In an audio stream loop, call your audio oscillator and write the sound to your audio device. Update the frequency of the audio oscillator in noteDuration time steps to follow the melody. As a best practice, release your objects once complete.
noteDuration = 0.3;
i = 1;
tic
while i < numel(melody)
tone = osc();
aDW(tone);
if toc >= noteDuration
i = i + 1;
osc.Frequency = melody(i);
tic
end
end
release(osc)
release(aDW)Create a low-frequency oscillator (LFO) lowpass filter, using the audioOscillator as a control signal.
Create dsp.AudioFileReader and audioDeviceWriter System objects to read from an audio file and write to your audio device. Create an SOS filter object to apply lowpass filtering to your audio signal.
fileReader = dsp.AudioFileReader('Filename','Engine-16-44p1-stereo-20sec.wav'); deviceWriter = audioDeviceWriter('SampleRate',fileReader.SampleRate); lowpassFilter = dsp.SOSFilter(CoefficientSource='Input port');
Create an audio oscillator object. Your audio oscillator controls the cutoff frequency of the lowpass filter in an audio stream loop.
osc = audioOscillator('SignalType','sawtooth', ... 'DCOffset',0.05, ... 'Amplitude',0.03, ... 'SamplesPerFrame',fileReader.SamplesPerFrame, ... 'SampleRate',fileReader.SampleRate, ... 'Frequency',5);
In a loop, filter the audio signal through the lowpass filter. Write the output signal to your audio device.
while ~isDone(fileReader) audioIn = fileReader(); ctrlSignal = osc(); [B,A] = designVarSlopeFilter(48,ctrlSignal(end),Orientation="row"); audioOut = lowpassFilter(audioIn,B,A); deviceWriter(audioOut); end
As a best practice, release objects once complete.
release(osc) release(fileReader) release(deviceWriter)
For a more complete implementation of an LFO Filter, see audiopluginexample.LFOFilter in the Audio Plugin Example Gallery.
