How to straighten a sinusoidal signal?

Question

Chinwe Orie 2018-6-25

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/407361-how-to-straighten-a-sinusoidal-signal

评论： Chinwe Orie 2018-6-26

I have a signal that bouncy (the waves are all over the place), and I've been trying to filter out the bouncy signals without changing the amplitude of the whole signal. Basically, I'd like a sinusoidal signal that is somewhat straight (doesn't have to be perfect). The data from the signal was imported from an excel file.

I have attached an image of what one of my signals look like. The problem with that particular signal is that little dip at the end of the signal that is very uneven with the rest of the waves.

Thanks for your help!

5 个评论
显示 3更早的评论隐藏 3更早的评论

Chinwe Orie 2018-6-25

Yes. I planned to take the envelope peaks of the signal and then subtract the upper envelopes from the lower ones to get the amplitude, but at the end the signal is uneven so taking the envelopes wouldn't be accurate there.

Greg Dionne 2018-6-26

There are a few ways to do this. Image Analyst's approach is good (remove the discontinuity, then filter). You can then view the spectrum (or spectrogram) to obtain the amplitude of the filtered signal.

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Image Analyst 2018-6-26

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/407361-how-to-straighten-a-sinusoidal-signal#answer_326369

在 MATLAB Online 中打开

It looks like the signal is going along just fine until suddenly there is a big jump, and then it's fine again. So rather than filter the whole signal, I'd just identify the jump locations, determine the new offset, and subtract that from the signal. Here is the code. It's s fast and simple for loop.

% Initialization steps.
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;
xy = xlsread('capture 2.xls');
x = xy(:, 1);
y = xy(:, 2);
subplot(3, 1, 1);
plot(x, y, 'b-');
grid on;
title('Original Signal', 'FontSize', fontSize);
subplot(3, 1, 2);
differences = [0; diff(y)];
plot(x, differences, 'b-');
grid on;
title('Difference Signal', 'FontSize', fontSize);
offset = 0;
for k = 1 : length(y)
  if abs(differences(k)) > 0.001
    offset = differences(k);
  end
  correctedSignal(k) = y(k) - offset;
end
subplot(3, 1, 3);
plot(x, correctedSignal, 'b-');
title('Corrected Signal', 'FontSize', fontSize);
grid on;
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0, 0.04, 1, 0.96]);

I think it does a pretty good job, don't you?

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Chinwe Orie 2018-6-26

This is more than a good job. Works with some other signals I have to. Thanks!

请先登录，再进行评论。

Answer 2

Image Analyst 2018-6-25

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/407361-how-to-straighten-a-sinusoidal-signal#answer_326232

在 MATLAB Online 中打开

I's use conv() to scan the signal with a window that covers an integer number of periods. Then I'd subtract the mean from the original signal. Something like

windowWidth = 31;  % Whatever works.
kernel = ones(windowWidth, 1)/windowWidth;
slidingMean = conv(signal, kernel, 'same');
correctedSignal = signal - slidingMean;

See how that works.