Clear Filters
Clear Filters

Synchronising two different signals

41 views (last 30 days)
Hello,
I am quite new to signal processing and I am trying my best to synchronize and align two signals that come from different devices.
One has a sample rate of 50 Hz and is recording acceleration with 3 axis (x, y and z). The other is recording ECG at 250Hz.
I have time marks of when both devices are turned on and off (which is different by max 10-20 seconds). Both seems to have 'time-drift', meaning that when looking at the data size, it never perfectly equals the size of Time*SampleRate. And even after resampling the 250Hz signal at 50Hz both data sizes have a small difference.
I have been trying different methods to align those signals but there is always a little delay between the two of them and I don't know what to do. I tried removing the time drift, synchronizing them with time-series, even the cross-correlation (even though I am not sure this can work since one of my signal has 3 axis)… Nothing seems to work.
So is there a way to know if there is major problem in one of the signals ?
Or is there another way of aligning/synchronizing those signals ?
I linked the two unfiltered signals.
Thanks,
Marine
  2 Comments
Star Strider
Star Strider on 15 Oct 2022
What are we to do with these?
Uz = unzip('https://www.mathworks.com/matlabcentral/answers/uploaded_files/1157478/Data.zip')
Uz = 1×8 cell array
{'Data/'} {'__MACOSX/._Data'} {'Data/.DS_Store'} {'__MACOSX/Data/._.DS_Store'} {'Data/ECG.csv'} {'__MACOSX/Data/._ECG.csv'} {'Data/Acceleration.csv'} {'__MACOSX/Data/._Acceleration.csv'}
EKG = readtable(Uz{5})
EKG = 904000×1 table
ECG_DATA ________ 680 1372 1740 1774 1805 1832 1853 1870 1883 1889 1884 1870 1850 1832 1815 1800
Acc = readtable(Uz{7})
Acc = 181412×18 table
Var1 Var2 Var3 Var4 Var5 Var6 Var7 Var8 Var9 Var10 Var11 Var12 Var13 Var14 Var15 Var16 Var17 Var18 ____ ____ _____ ____ ____ ____ ____ ____ ____ ______________________ _____ _____ _____ ______ _____ _____ _____ _____ -106 -203 -1969 -157 151 -17 -32 54 -178 {0×0 char } NaN NaN NaN NaN NaN NaN NaN NaN 18 -87 -2052 -169 159 -17 -230 309 -296 {0×0 char } NaN NaN NaN NaN NaN NaN NaN NaN 129 -13 -2062 -169 151 -13 -140 245 -250 {0×0 char } NaN NaN NaN NaN NaN NaN NaN NaN 108 -85 -2073 -159 149 -23 -93 166 -129 {0×0 char } NaN NaN NaN NaN NaN NaN NaN NaN 66 -152 -2119 -169 149 -15 47 89 -143 {0×0 char } NaN NaN NaN NaN NaN NaN NaN NaN 81 -114 -2010 -165 145 -11 116 4 -155 {0×0 char } NaN NaN NaN NaN NaN NaN NaN NaN 59 -109 -2118 -170 148 -26 68 77 -144 {0×0 char } NaN NaN NaN NaN NaN NaN NaN NaN 154 -53 -1999 -163 143 -25 189 -35 -117 {0×0 char } NaN NaN NaN NaN NaN NaN NaN NaN 125 12 -1975 -158 156 -26 221 -132 56 {0×0 char } NaN NaN NaN NaN NaN NaN NaN NaN 9 -110 -2064 -162 142 -20 220 -267 108 {'22-10-11T09:55:47Z'} 105 266 236 1016.5 0.06 25.17 0 4.1 -59 -226 -1893 -162 152 -26 220 -182 78 {0×0 char } NaN NaN NaN NaN NaN NaN NaN NaN -107 -329 -2100 -160 152 -22 -321 271 -124 {0×0 char } NaN NaN NaN NaN NaN NaN NaN NaN 13 -156 -2148 -158 154 -28 -371 359 -235 {0×0 char } NaN NaN NaN NaN NaN NaN NaN NaN 197 -5 -2076 -166 154 -26 -249 290 -205 {0×0 char } NaN NaN NaN NaN NaN NaN NaN NaN 175 -65 -2140 -162 154 -22 21 32 -70 {0×0 char } NaN NaN NaN NaN NaN NaN NaN NaN 84 -178 -1973 -159 141 -27 201 -198 -47 {0×0 char } NaN NaN NaN NaN NaN NaN NaN NaN
Just looking at them, I have no idea.
.
Marpe
Marpe on 15 Oct 2022
Yes sorry I forgot to share my code. This one of my trial to better understand.

Sign in to comment.

Accepted Answer

Star Strider
Star Strider on 15 Oct 2022
I got this far, however I have no idea what you want to do with them at this point —
% clear
% close all
% datapathECG = %Data path;
% dECG = dir(datapathECG);
% nd = length(dir);
Uz = unzip('https://www.mathworks.com/matlabcentral/answers/uploaded_files/1157478/Data.zip');
% EKG = readtable(Uz{5})
% Acc = readtable(Uz{7})
%ECG data
for n=10
% file=[datapathECG,dECG(n).name];
% tbl = readtable(file);
tbl = readtable(Uz{5});
ecg=table2array(tbl);
[~,~]=size(ecg);
Fs1 = 250;
%Resampling of ECG from 250Hz to 50Hz
ecg=resample(ecg,50,Fs1);
[Necg,~]=size(ecg);
end
%Acceleration data
% close all
% datapathAcc= % Data path to data files
% dAcc=dir(datapathAcc);
% nd=length(dir);
for n=5
% file=[datapathAcc,dAcc(n).name];
% tbl = readtable(file);
tbl = readtable(Uz{7});
acctab=tbl(:,1:3);
Tacc=tbl(:,10);
acctab = table2array(acctab);
[Nacc,dum]=size(acctab);
Fs2=50;
end
%Remove drift in both
%ECG
StartECG = datetime(2022,10,11,07,56,40,'TimeZone','UTC');
StartECG.Format = 'hh:mm:ss';
Stop = datetime(2022,10,11,08,57,10,'TimeZone','UTC');
Stop.Format = 'hh:mm:ss';
Fs = 50;
Time = seconds(Stop - StartECG);
Nth = (Time.*Fs);
drift = Nth - Necg;
drift = drift/Fs;
drift = Nth/drift;
drift1 = round(drift/Fs);
ecg(drift1:drift1:end,:) = [];
[Necg,d]=size(ecg);
%Acceleration
DT = datetime(Tacc.Var10, 'InputFormat','yy-MM-dd''T''HHH:mm:ss''Z''','TimeZone','UTC');
DT.Format = 'hh:mm:ss';
DTnew = fillmissing(DT,'linear');
StartR = DTnew(1,1);
disp('Real = ');
Real =
disp(StartR);
09:55:47
StartR = datetime(StartR,"TimeZone","UTC");
StartR.Format = 'hh:mm:ss';
%Have to change everytime
StartTH = datetime(2022,10,11,07,55,20,'TimeZone','UTC');
StartTH.Format = 'hh:mm:ss';
disp('Theory = ');
Theory =
disp(StartTH);
07:55:20
delay = abs(StartR - StartTH);
StartACC = StartR - delay;
Stop = datetime(2022,10,11,08,56,10,'TimeZone','UTC');
Stop.Format = 'hh:mm:ss';
Fs = 50;
Time = seconds(Stop - StartACC);
Nth = (Time.*Fs);
drift = Nth - Nacc;
drift = drift/Fs;
drift = Nth/drift;
drift2 = round(drift/Fs);
acctab(drift2:drift2:end,:) = [];
[Nacc,d]=size(acctab);
%Time for ECG
time=StartECG;
time.Format= 'hh:mm:ss';
s1=seconds(1/Fs2:1/Fs2:Necg/Fs2);
T=time+s1;
Tecg = timetable(T',ecg);
%Time for Acceleration data
time=StartACC;
time.Format= 'hh:mm:ss';
s1=seconds(1/Fs2:1/Fs2:Nacc/Fs2);
T=time+s1;
Tacc = timetable(T',acctab);
TT = synchronize(Tecg,Tacc,"union","nearest");
stackedplot(TT.Time,TT.Variables);
Or, to put it differently, I do not see a problem. You have several different signals all sharing the same time vector. (I have no idea what they refer to, or what you want to wo with them.)
.
  6 Comments
Marpe
Marpe on 15 Oct 2022
Thank you very much for your help !

Sign in to comment.

More Answers (0)

Categories

Find more on Signal Processing Toolbox in Help Center and File Exchange

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!