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.

reader = dsp.AudioFileReader('guitar_plus_tone.ogg');

scope = dsp.SpectrumAnalyzer('SampleRate',reader.SampleRate, ...
    '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');

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.

tic
helperAudioToneRemoval
t1 = toc;

fprintf('MATLAB Simulation Time: %d\n',t1)

MATLAB Simulation Time: 3.701829e+00

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

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)

Code Generation Simulation Time: 2.167587e+00

fprintf('Speedup factor: %6.2f\n',t1/t2)

Speedup factor:   1.71