Question about peak detection

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Teapotimus
Teapotimus 2020-3-12
回答： Cris LaPierre 2020-3-12
I've written a script to find the percussive peaks of a provided icp signal, I'm very close but the markers I'm placing are off. I believe this is representative of my script marking them at the wrong index, just not sure how to fix this.
%% Plot ICP in Time Domain
clc; clear all; close all;
load icp;
t = (0:length(icp)-1)/fs;
figure('Color',[1 1 1]);
plot(t,icp);
%% Highpass, Remove DC Trend
fchp = 0.5;
Wp = fchp/(fs/2);
[B1,A1] = ellip(4,0.5,20,Wp,'high');
icphp = filtfilt(B1,A1,icp);
figure('Color',[1 1 1]);
h = plot(t,icphp);
figure('Color', [1 1 1]);
freqz(B1,A1,2^12,fs);
figure('Color',[1 1 1]);
zplane(B1,A1);
%% Lowpass, smooth signal
fclp = 3;
Wp = fclp/(fs/2);
[B2,A2] = ellip(2,0.5,20,Wp);
icplp = filtfilt(B2,A2,icphp);
figure('Color',[1 1 1]);
h = plot(t,icplp);
figure('Color', [1 1 1]);
freqz(B2,A2,2^12,fs);
figure('Color',[1 1 1]);
zplane(B2,A2);
%% Differentiator
icpd = diff([0;icphp]);
figure('Color',[1 1 1]);
h = plot(t,icpd);
set(h,'Color',[0.1 0.1 .1]);
set(h, 'Linewidth', 2);
%% Square Operator
icps = icpd.^2;
h = plot(t,icps);
set(h,'Color',[0.5 1 1]);
set(h,'Linewidth', 2);
xlabel('Time (s)');
ylabel('ICP');
box off; hold on;
%% Moving AVerage filter
B = 1/30*ones(30,1);
icpm = filtfilt(B,1,icps);
figure('Color', [1 1 1]);
h = plot(t,icpm);
set(h,'Color', [0.5 0.5 1]);
set(h,'Linewidth', 2);
title('Moving Average Filter');
%% Decision Logic
x = icpm;
L = length(x);
id = find((x(1:L-2)<x(2:L-1))&(x(2:L-1)>x(3:L)))+1;
id2 = find(icp(id) > 1);
id2 = id(id2);
figure('Color',[1 1 1]);
h = plot(t, x, id/fs, x(id), 'r.');
set(h,'Markersize', 18);
title('Decision Logic');
%% Detection On Original Signal
figure('Color',[1 1 1]);
h = plot(t,icp,id2/fs,icp(id2),'r.');
set(h,'Markersize', 18);
set(h,'Linewidth', 2);
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Adam
Adam 2020-3-12
编辑：Adam 2020-3-12
Are the markers off by just one sample or more? And is it always the same amount? It looks like maybe more than 1 sample, but it can be hard to tell on steep sections of curve like that. If it is only 1 it may just be a matter of re-checking your code that calculates them to make sure the indices you are actually calculating are those of the peak point rather than the point just before the peak (e.g. using previous, current and next points to check for peaks, is your code returning the index of 'previous' rather than 'current', the centre point containing the actual peak?). There's often some +/- 1 logic that can easily get missed out or applied the wrong way with indexing things, especially when dividing by sample rates too.
Teapotimus
Teapotimus 2020-3-12
Should have attached this in the first place

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Cris LaPierre
Cris LaPierre 2020-3-12
Do you have the Signal Processing toolbox? This can be accomplished with the findpeaks function.
[pk,loc]=findpeaks(icp,"MinPeakDistance",40);
t = (0:length(icp)-1)/fs;
figure
plot(t,icp)
hold on
plot(t(loc),pk,'r.')
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