Increasing the amplitude of the sine

Hello ! Is it possible to increase the amplitude of sine and then plot the sine ? Basically i want to plot a sine with a small amplitude which is getting bigger over the time. And last, i want to make it visible, so i can see the change of the amplitude. I thought about using a for loop, but it didn't worked out like i imagined. (Btw English is not my first language, sorry about that..)

Answer 1

[Image Analyst]

Try this:

% Define a time axis:
t = 0 : 0.1 : 20;
% Define the period
period = 3;
% Make a function for how the amplitude varies with time:
% For example the amplitude is the square root of time, 
% or whatever formula you want to use.
amplitude = sqrt(t);
% Now make the sine wave
y = amplitude .* sin(2 * pi * t / period);
plot(t, y, 'b-');
grid on;

[Jack Walker]

Hi, thank you very much for help !! Now I understand it. Thanks again.

[Image Analyst]

You're welcome. You can "Accept" only one answer but you can "Vote" for as many as you want.

[Andy Nguyen]

can you play the audio from this with sound()? how would you go about playing the sine wave for this?

[Image Analyst]

Try the sound() or soundsc() function.

[Andy Nguyen]

did not work unfortunately, for sound(); it needs a constant, and it gives a finite scalar value error due to "t = 0 : 0.1 : 20;"

[yanqi liu]

t = 0 : 0.01 : 20;
% Define the period
period = 3;
% Make a function for how the amplitude varies with time:
% For example the amplitude is the square root of time, 
% or whatever formula you want to use.
amplitude = sqrt(t);
% Now make the sine wave
y = amplitude .* sin(2 * pi * t / period);
plot(t, y, 'b-');
grid on;
sound(y)

[Image Analyst]

3 Hz is way too low a frequency of sound to hear. You'll need to have a higher frequency. Try this attached demo to see how to make a sound that you can hear:

% Program to create a warbling wave file with variable amplitude and pitch.
% function make_wav_file()
% Initialization / clean-up code.
clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
clear;  % Erase all existing variables. Or clearvars if you want.
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 20;
% Create the filename where we will save the waveform.
folder = pwd;
baseFileName = 'Test_Wave.wav';
fullFileName = fullfile(folder, baseFileName);
fprintf('Full File Name = %s\n', fullFileName);
% Set up the time axis:
Fs = 8000;
duration = 2; % seconds.
t = 1 : duration * Fs; % 2 seconds
% Set up the period (pitch, frequency):
T = 13; % Constant pitch if you use this.
T = linspace(25, 8, length(t)); % Pitch changes if you use this.
% Create the maximum amplitude:
Amplitude = 32767;
% Add an exponential decay:
Amplitude = Amplitude .* exp(-0.0003*t);
% Add an ocillation on the amplitude:
% Amplitude = Amplitude .* rand(1, length(x)); % Makes a shushing/roaring sound.
Amplitude = Amplitude .* sin(2.*pi.*t./2000); % Decaying pulsing sound.
% Construct the waveform:
y = int16(Amplitude .* sin(2.*pi.*t./T));
% y = abs(int16(Amplitude .* sin(2.*pi.*x./T)));
% Plot the waveform:
plot(t, y, 'b-');
title('Waveform', 'FontSize', fontSize);
xlabel('Time', 'FontSize', fontSize);
ylabel('Y', 'FontSize', fontSize);
grid on;
% Enlarge figure to full screen.
set(gcf, 'units','normalized','outerposition',[0 0 1 1]);
fprintf('Writing file %s...\n', fullFileName);
% Write the waveform to a file:
audiowrite(fullFileName, y, Fs);
% Play the sound as many times as the user wants.
playAgain = true;
counter = 1;
while playAgain
    % Play the sound that we just created.
    fprintf('Playing file %s   %d times...\n', fullFileName, counter);
    player = audioplayer(y, Fs);
    play(player);
    % Ask user if they want to play the sound again.
    promptMessage = sprintf('You have played the sound %d times.\nDo you want to play the sound again?', counter);
    titleBarCaption = 'Continue?';
    button = questdlg(promptMessage, titleBarCaption, 'Yes', 'No', 'Yes');
    if strcmpi(button, 'No')
        playAgain = false;
        break;
    end
    counter = counter + 1;
end
% Alert user that we are done.
message = sprintf('Done playing %s.\n', fullFileName);
fprintf('%s\n', message);
promptMessage = sprintf('Done playing %s.\nClick OK to close the window\nor Cancel to leave it up.', fullFileName);
titleBarCaption = 'Continue?';
button = questdlg(promptMessage, titleBarCaption, 'OK', 'Cancel', 'OK');
if strcmpi(button, 'OK')
    close all;	% Close down the figure.
end

Answer 2

[Robert Steidl]

I possibly do have a solution for your Problem - with minor Settings to solve it! Maybe it is a good init to your case!

At first I have declined my time variable for three Sine - then I set a variable over one period that changes in my for Loop! At the end I have three sine with three different amplitudes in a row!

if true
  t=0:pi/16:6*pi;
  temp = 1;
  for i=1:3
   k(temp:find(t==i*2*pi))=i;
   temp=length(k);
  end
  y=k.*sin(t);
  plot(t,y)
end

Hope that helps

[Jack Walker]

Hi Robert ! Thank you very much for your answer. It was exactly what i needed. But could you explain, what the term " k(temp:find(t==i*2*pi))=i;" means ? I have a vague idea, but i am not quite sure. Sorry for bothering you !