Plotting one cycle of a wave

[sig, fs] = audioread(x);
modfreq = 4;
depth = 100;
a = depth/200;
offset = 1 - a;
len = 1:length(sig); 
phasor = a*sawtooth(2*pi*len*(modfreq/fs)) +offset;

I'm generating a wave for a tremolo. I know how to plot the entire wave(at the length of the input signal), however I would like to be able to plot just a single cycle.

I found an answer in a previous question:

fs = 512; % Sampling frequency (samples per second) 
 dt = 1/fs; % seconds per sample 
 StopTime = 0.25; % seconds 
 t = (0:dt:StopTime)'; % seconds 
 F = 60; % Sine wave frequency (hertz) 
 data = sin(2*pi*F*t);
 plot(t,data)
 %%For one cycle get time period
 T = 1/F ;
 % time step for one time period 
 tt = 0:dt:T+dt ;
 d = sin(2*pi*F*tt) ;
 plot(tt,d) ;

However, it generates a second wave at a shorter length. I would like to be able to plot just one cycle of the original wave without creating a second.

Does anyone know how to do this?

Thanks in advance.

[madhan ravi]

you want to restrict the range ? that's what you mean?

Answer 1

[Omer Yasin Birey]

I believe axis() would work. I wrote an example code with a signal which has cycles.

x = 1:100;
signal = (1-cos(2*pi*0.01*x)).*sin(2*pi*0.15*x);%signal with cycles
plot(signal,'r-')

[peak,locs] = findpeaks(-signal);   % Find Minimas
%you can use loop to plot every single cycle. it is just for the first one
firstInd = locs(1);%use a minima and the next one to find cycle limits
lastInd = locs(2);
%limit the plot with the start and end of the both x and y axes
axis([firstInd lastInd -peak(1) peak(2)]) 

[William Chambers]

Thanks for this, I managed to get it working in my test script, but when I try to implement it within the app designer it doesn't work.

             T = 1/modfreq ;
             dt = 1/fs;
             tt = 0:dt:T+dt ;
             
             plot(app.UIAxes, len, wave)
             axis([0 length(tt) 0 1])

I've left out some parts of the code in this snippet, but you should get the idea of what I'm trying to do. When I run the app desginer app, it just plots the unlimited range plot (all cycles) and a random blank graph.

[Omer Yasin Birey]

I think length(tt) is the problem here. Because you start from 0 to length(tt), which means the whole range of signal and tt might have a very long sequence. Finding the 2 minimas, left and right, which are bounding a cycle still seems the possible solution to me.

T = 1/modfreq ;
dt = 1/fs;
tt = 0:dt:T+dt ;
[peak,locs] = findpeaks(-signal);  
for i = 1:2:length(locs)-2
    figure
    firstInd = locs(i);
    lastInd = locs(i+1);
    plot(app.UIAxes, len, wave)
    axis([firstInd lastInd -peak(i) peak(i+1)]) 
end

This code above should plot all the cycles seperately.

Answer 2

[Rohan Basak]

T = 1/modfreq ;
dt = 1/fs;
tt = 0:dt:T+dt ;
[peak,locs] = findpeaks(-signal);
for i = 1:2:length(locs)-2
    figure
    firstInd = locs(i);
    lastInd = locs(i+1);
    plot(app.UIAxes, len, wave)
    axis([firstInd lastInd -peak(i) peak(i+1)])
end

[Walter Roberson]

Rohan Basak:

Why are you create a new figure each time, even though you are plotting on a fixed axes?

Note also that the axis() command you are using is going to apply to the "current" axis, which is going to be a newly generated axes in the newly generated figure.