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Desktop Real-Time Audio Acceleration with MATLAB Coder

This example shows how to accelerate a real-time audio application using C code generation with MATLAB® Coder™. You must have the MATLAB Coder™ software installed to run this example.

Introduction

Replacing parts of your MATLAB code with an automatically generated MATLAB executable (MEX-function) can speed up simulation. Using MATLAB Coder, you can generate readable and portable C code and compile it into a MEX-function that replaces the equivalent section of your MATLAB algorithm.

This example showcases code generation using an audio notch filtering application.

Notch Filtering

A notch filter is used to eliminate a specific frequency from a signal. Typical filter design parameters for notch filters are the notch center frequency and the 3 dB bandwidth. The center frequency is the frequency at which the filter has a linear gain of zero. The 3 dB bandwidth measures the frequency width of the notch of the filter computed at the half-power or 3 dB attenuation point.

The helper function used in this example is helperAudioToneRemoval. The function reads an audio signal corrupted by a 250 Hz sinusoidal tone from a file. helperAudioToneRemoval uses a notch filter to remove the interfering tone and writes the filtered signal to a file.

You can visualize the corrupted audio signal using a spectrum analyzer.

scope = dsp.SpectrumAnalyzer('SampleRate',44.1e3,...
    'RBWSource','Property','RBW',5,...
    'PlotAsTwoSidedSpectrum',false,...
    'SpectralAverages',10,...
    'FrequencySpan','Start and stop frequencies',...
    'StartFrequency',20,...
    'StopFrequency',1000,...
    'Title','Audio signal corrupted by 250 Hz tone');
reader = dsp.AudioFileReader('guitar_plus_tone.ogg');

while ~isDone(reader)
    audio = reader();
    scope(audio(:,1));
end

C Code Generation Speedup

Measure the time it takes to read the audio file, filter out the interfering tone, and write the filtered output using MATLAB code. Because helperAudioToneRemoval writes an audio file output, you must have write permission in the current directory. To ensure write access, change directory to your system's temporary folder.

mydir = pwd; addpath(mydir); cd(tempdir);
tic;
helperAudioToneRemoval;
t1 = toc;
fprintf('MATLAB Simulation Time: %d\n',t1);
MATLAB Simulation Time: 5.342373e+00

Next, generate a MEX-function from helperAudioToneRemoval using the MATLAB Coder function, codegen.

codegen helperAudioToneRemoval

Measure the time it takes to execute the MEX-function and calculate the speedup gain with a compiled function.

tic;
helperAudioToneRemoval_mex
t2 = toc;
fprintf('Code Generation Simulation Time: %d\n',t2);
fprintf('Speedup factor: %6.2f\n',t1/t2);

cd(mydir);
Code Generation Simulation Time: 2.498943e+00
Speedup factor:   2.14

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