Generate periodic signal from single-cycle waveforms
System object™ generates a periodic signal with tunable properties. The periodic signal is
defined by a single-cycle waveform cached as the
Wavetable property of
To generate a periodic signal:
wavetableSynthesizerobject 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?
wavetable synthesizer System object,
waveSynth = wavetableSynthesizer
waveSynth, with default property values.
sets the Wavetable
waveSynth = wavetableSynthesizer(
sets the Frequency
waveSynth = wavetableSynthesizer(
waveSynth = wavetableSynthesizer(___,
sets each property
Name to the specified
Unspecified properties have default values.
wavetableSynthesizer('Amplitude',2,'DCOffset',2.5) creates a System object,
waveSynth, that generates the default sine waveform with
an amplitude of 2 and a DC offset of 2.5.
Unless otherwise indicated, properties are nontunable, which means you cannot change their
values after calling the object. Objects lock when you call them, and the
release function unlocks them.
If a property is tunable, you can change its value at any time.
For more information on changing property values, see System Design in MATLAB Using System Objects.
Wavetable — Single-cycle waveform
sin(2*pi*(0:511)/512) (default) | vector of real values
Single-cycle waveform, specified as a vector of real values. The algorithm of the
wavetableSynthesizer indexes into the single-cycle
waveform to synthesize a periodic wave.
Frequency — Frequency of generated signal (Hz)
100 (default) | real scalar
Frequency of generated signal in Hz, specified as a real scalar greater than or equal to 0.
Amplitude — Amplitude of generated signal
1 (default) | real scalar
Amplitude of generated signal, specified as a real scalar greater than or equal to 0.
The generated signal is multiplied by the value specified by
Amplitude at the output, before DCOffset is
PhaseOffset — Normalized phase offset of generated signal
0 (default) | real scalar
Normalized phase offset of generated signal, specified as a real scalar with values in the range [0, 1]. The range is a normalized 2π radians interval.
DCOffset — Value added to each element of generated signal
0 (default) | real scalar
Value added to each element of the generated signal, specified as a real scalar.
SamplesPerFrame — Number of samples per frame
512 (default) | positive integer
Number of samples per frame, specified as a positive integer in the range [1, 192000].
This property determines the vector length that your
wavetableSynthesizer object outputs.
SampleRate — Sample rate of generated signal (Hz)
44100 (default) | real positive scalar
Sample rate of generated signal in Hz, specified as a real positive scalar.
OutputDataType — Data type of generated signal
'double' (default) |
Data type of generated signal, specified as
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
Specific to wavetableSynthesizer
functions map tunable properties of the
System object to user-facing parameters:
Generate Variable-Frequency Staircase Wave
Define and plot a single-cycle waveform.
values = -1:0.1:1; singleCycleWave = ones(100,1) * values; singleCycleWave = reshape(singleCycleWave,numel(singleCycleWave),1); plot(singleCycleWave) xlabel('Index') ylabel('Amplitude')
Create a wavetable synthesizer,
waveSynth, to generate a staircase wave using the single-cycle waveform. Specify a frequency of 10 Hz.
waveSynth = wavetableSynthesizer(singleCycleWave,10);
Create a time scope to visualize the staircase wave generated by
scope = timescope( ... 'SampleRate',waveSynth.SampleRate, ... 'TimeSpanSource','Property','TimeSpan',0.1, ... 'YLimits',[-1.5,1.5], ... 'TimeSpanOverrunAction','Scroll', ... 'ShowGrid',true, ... 'Title','Variable-Frequency Staircase Wave');
Place the wavetable synthesizer in an audio stream loop. Increase the frequency of your staircase wave in 10 Hz increments.
counter = 0; while (counter < 1e4) counter = counter + 1; staircaseWave = waveSynth(); scope(staircaseWave) if mod(counter,1000)==0 waveSynth.Frequency = waveSynth.Frequency + 10; end end
Manipulate Audio Samples Using Wavetable Synthesizer
Sample an audio file and save it to the
Wavetable property of a
wavetableSynthesizer System object™. Use the wavetable synthesizer to manipulate your audio sample.
Read in an entire audio file. Clip out an interesting sound from the audio and then play it.
[audio,fs] = audioread('MainStreetOne-16-16-mono-12secs.wav'); aSound = audio(2.5e4:5e4); sound(aSound,fs)
Create a wavetable synthesizer using your audio clip. The duration of the
engine audio clip is
numel(aSound)/fs seconds. In the
wavetableSynthesizer, set the
Frequency property to 1/(clip duration). The generated signal now plays back at the same rate it was recorded at.
duration = numel(aSound)/fs; waveSynth = wavetableSynthesizer('Wavetable',aSound,'SampleRate',fs, ... 'Frequency',1/duration);
audioDeviceWriter to write to your audio device.
deviceWriter = audioDeviceWriter('SampleRate',fs);
In a loop, play the wavetable synthesizer to your device. After three seconds, begin increasing the frequency of the wavetable synthesizer. After six seconds, begin decreasing the frequency of the wavetable synthesizer.
timeElapsed = 0; while timeElapsed < 9 audioWave = waveSynth(); deviceWriter(audioWave); if (timeElapsed > 3) && (timeElapsed < 6) waveSynth.Frequency = waveSynth.Frequency + 0.001; elseif timeElapsed > 6 waveSynth.Frequency = waveSynth.Frequency - 0.002; end timeElapsed = timeElapsed + waveSynth.SamplesPerFrame*(1/fs); end
Modify Wavetable While Stream Processing
Wavetable property of a
wavetableSynthesizer object while stream processing. Visualize the wavetable and play the resulting audio.
Create a single-cycle waveform for the
wavetableSynthesizer to index into. Create a wavetable synthesizer object.
t = 0:0.001:1; exponent = 5; waveTable = [t.^exponent,fliplr(t.^exponent)] - 0.5; waveSynth = wavetableSynthesizer('Wavetable',waveTable);
dsp.ArrayPlot object to plot the wavetable as it is modified over time. Create an
audioDeviceWriter object to listen to the signal output by your wavetable synthesizer.
arrayPlotter = dsp.ArrayPlot('YLimits',[-1,1],'PlotType','Line'); deviceWriter = audioDeviceWriter;
In an audio stream loop, incrementally modify the
Wavetable property of the wavetable synthesizer and plot it. Call the synthesizer to output a waveform and play the waveform to your audio device.
tic while toc < 10 exponent = exponent - 0.01; waveSynth.Wavetable = [t.^abs(exponent),fliplr(t.^abs(exponent))] - 0.5; arrayPlotter(waveSynth.Wavetable') deviceWriter(waveSynth()); end
Tune Wavetable Synthesizer Parameters
wavetableSynthesizer to generate a waveform. Create a
timescope to visualize the waveform. Create an
audioDeviceWriter to write audio to your sound card.
fs = 44.1e3; wvSynth = wavetableSynthesizer('SampleRate',fs); scope = timescope( ... 'SampleRate',wvSynth.SampleRate, ... 'TimeSpanSource','Property','TimeSpan',1, ... 'YLimits',[-2,2], ... 'TimeSpanOverrunAction','Scroll', ... 'ShowGrid',true); deviceWriter = audioDeviceWriter('SampleRate',wvSynth.SampleRate);
parameterTuner to open a UI to tune parameters of the wavetable synthesizer while streaming.
In an audio stream loop:
Call the wavetable synthesizer without arguments to output one frame of data.
Visualize the data using the time scope.
Write the frame of audio to your audio device for listening.
While streaming, tune parameters of the wavetable synthesizer and listen to the effect.
duration = 15; numIterations = round(wvSynth.SampleRate*duration/wvSynth.SamplesPerFrame); for i = 1:numIterations audioOut = wvSynth(); scope(audioOut) deviceWriter(audioOut); drawnow limitrate % required to update parameter end
As a best practice, release your objects when done.
release(deviceWriter) release(wvSynth) release(scope)
System object synthesizes periodic signals using a cached single-cycle waveform, specified
waveform properties, and phase memory.
Compute the increment step size:
where N is the number of elements in your wavetable.
Compute Wavetable Index
for . The
PhaseOffset property determines
Index into the
Wavetable and perform linear interpolation:
Apply Amplitude and DC Offset
Amplitude and add
C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.
Usage notes and limitations:
System Objects in MATLAB Code Generation (MATLAB Coder)