# Dash MATLAB Example: Signal with FFT and noise **URL:** \ **Category:** Dash for MATLAB®\ **Created:** [September 28, 2021, 7:13pm UTC](https://community.plotly.com/t/dash-matlab-example-signal-with-fft-and-noise/57086 "2021-09-28T19:13:08Z")\ **Posts on this page:** 1\ **Page:** 1
**Author:** ![carlosp](https://sea2.discourse-cdn.com/flex024/user_avatar/community.plotly.com/carlosp/32/16513_2.png) [@carlosp](https://community.plotly.com/u/carlosp)\ **Post date:** [September 28, 2021, 7:13pm UTC](https://community.plotly.com/t/dash-matlab-example-signal-with-fft-and-noise/57086/1 "2021-09-28T19:13:08Z")
> New to Dash MATLAB®? See: > > - [About the Dash for MATLAB® category](https://community.plotly.com/t/about-the-dash-for-matlab-category/56545) > - [Dash MATLAB® Quickstart. Part I: Download and install](https://community.plotly.com/t/dash-matlab-quickstart-part-i-download-and-install/56937) > - [Dash MATLAB® Quickstart. Part II: Making your first app](https://community.plotly.com/t/dash-matlab-quickstart-part-ii-making-your-first-app/57004) > - [Dash MATLAB® Quickstart. Part III: App layout with bar graph](https://community.plotly.com/t/dash-matlab-quickstart-part-iii-layout-with-bar-graph/56974) > - [Official Dash docs for MATLAB®](https://dash.plotly.com/matlab/) > > Follow [this link](https://community.plotly.com/c/dash/matlab/27) to see more examples and learn how to use Dash for MATLAB®! > > We encorage you to ask any questions you may have about Dash for MATLAB®. We are here to help! You can also share your ideas with the community. In this example we are going to see how can we make a Dash app with some signal, and compute its [Fast Fourier Transform](https://www.mathworks.com/help/matlab/ref/fft.html). This app will have two subplots (one for the original signal, and another for the fft), four sliders, and a [boolean swtich](https://www.mathworks.com/help/matlab/ref/uiswitch.html). The function we are going to use is: **A1·Sin(2·π·f1·t) + A2·Sin(2·π·f2·t)** Therefore we have one slider for each parameter: **A1** , **A2** , **f1** and **f2**. The boolean switch lets us choose whether we want to add a random noise to the signal or not. The running app looks like this: ![fftExample](https://us1.discourse-cdn.com/flex024/uploads/plot/original/3X/b/8/b86b2507d8d6bf1c526cf14059262f2bfcd68ab9.gif) Make a new MATLAB script called `fftApp.m` with the following code: ```auto terminate(pyenv); clearvars; uiFigure = uifigure('visible', 'off'); size = [12, 12]; uiGrid = uigridlayout(uiFigure, size); % Initial Plot ax = axes(uiGrid); ax.Tag = 'my-plot'; % Toggle FFT switch switchButton = uiswitch(uiGrid, 'Tag', 'my-switch'); switchButton.Layout.Row = 1; switchButton.Layout.Column = 8; switchLabel = uilabel(uiGrid, 'Text', 'Touch to add/remove noise',... 'FontSize', 14, 'FontColor', 'white'); switchLabel.Layout.Row = 1; switchLabel.Layout.Column = 8; % Frequency 1 frequencySlider1 = uislider(uiGrid, 'Tag', 'freq-slider-1'); frequencySlider1.Value = 50; frequencySlider1.MajorTicks = (0:25:500); frequencySlider1.Layout.Row = 3; frequencySlider1.Layout.Column = [1, 6]; frequencyLabel1 = uilabel(uiGrid, 'Text', 'Frequency 1',... 'FontSize', 16, 'FontWeight', 'bold', 'FontColor', 'white'); frequencyLabel1.Layout.Row = 2; frequencyLabel1.Layout.Column = [2, 4]; % Frequency 2 frequencySlider2 = uislider(uiGrid, 'Tag', 'freq-slider-2'); frequencySlider2.Limits = [0 140]; frequencySlider2.Value = 125.0; frequencySlider2.MajorTicks = (0:25:500); frequencySlider2.Layout.Row = 3; frequencySlider2.Layout.Column = [7, 12]; frequencyLabel1 = uilabel(uiGrid, 'Text', 'Frequency 2',... 'FontSize', 16, 'FontWeight', 'bold', 'FontColor', 'white'); frequencyLabel1.Layout.Row = 2; frequencyLabel1.Layout.Column = [9, 11]; % Amplitude 1 amplitudeSlider1 = uislider(uiGrid, 'Tag', 'ampl-slider-1'); amplitudeSlider1.Value = 0.7; amplitudeSlider1.MajorTicks = (0:0.1:2); amplitudeSlider1.Layout.Row = 5; amplitudeSlider1.Layout.Column = [1, 6]; amplitudeLabel1 = uilabel(uiGrid, 'Text', 'Amplitude 1',... 'FontSize', 16, 'FontWeight', 'bold', 'FontColor', 'white'); amplitudeLabel1.Layout.Row = 4; amplitudeLabel1.Layout.Column = [2, 4]; % Amplitude 2 amplitudeSlider2 = uislider(uiGrid, 'Tag', 'ampl-slider-2'); amplitudeSlider2.Value = 1.0; amplitudeSlider2.MajorTicks = (0:0.1:2); amplitudeSlider2.Layout.Row = 5; amplitudeSlider2.Layout.Column = [7, 12]; amplitudeLabel2 = uilabel(uiGrid, 'Text', 'Amplitude 2',... 'FontSize', 16, 'FontWeight', 'bold', 'FontColor', 'white'); amplitudeLabel2.Layout.Row = 4; amplitudeLabel2.Layout.Column = [9, 11]; args = {... argsOut('my-plot', 'figure'),... argsIn('freq-slider-1','value'),... argsIn('freq-slider-2','value'),... argsIn('ampl-slider-1','value'),... argsIn('ampl-slider-2','value'),... argsIn('my-switch','on')}; handle = 'updateGraph'; % Callback function callbackDat = {args, handle}; % run the app startDash(uiGrid, 8057, callbackDat, 'SOLAR'); ``` The callback function `updateGraph.m`: ```auto function plotlyFig = updateGraph(freq1, freq2, amp1, amp2, noiseButton) F1 = double(freq1); F2 = double(freq2); A1 = double(amp1); A2 = double(amp2); % Signal subplot(2,1,1); Fs = 1000; % Sampling frequency T = 1/Fs; % Sampling period L = 1500; % Length of signal t = (0:L-1)*T; % Time vector S = A1*sin(2*pi*F1*t) + A2*sin(2*pi*F2*t); if strcmp(string(noiseButton), 'true') X = S + 2*randn(size(t)); else X = S; end plot(1000*t(1:50),X(1:50), 'LineWidth', 1.5) title(A1+"·sin(2·π·"+F1+"·t)+"+... A2+"·sin(2·π·"+F2+"·t)", 'FontSize', 16) xlabel('t (milliseconds)', 'FontSize', 14) ylabel('X(t)', 'FontSize', 14) % Compute FFT subplot(2,1,2); Y = fft(X); P2 = abs(Y/L); P1 = P2(1:L/2+1); P1(2:end-1) = 2*P1(2:end-1); f = Fs*(0:(L/2))/L; plot(f,P1, 'LineWidth', 1.5) title('Single-Sided Amplitude Spectrum of X(t)', 'FontSize', 16) xlabel('f (Hz)', 'FontSize', 14) ylabel('|P1(f)|', 'FontSize', 14) fig = fig2plotly(gcf, 'offline', true, 'open', false, 'Visible', false); addtheme(fig, 'plotly_dark'); plotlyFig1 = {struct('data', {fig.('data')}, 'layout', fig.('layout'))}; plotlyFig = char(jsonencode(plotlyFig1)); end ``` You can try to add a third term to the signal, or you can try to include a custom signal from an external file!