I am tyring to produce a power spectrum graph for a Tachogram data,
related to Heart Rate Variability Analysis. This data can be thought
to be as a random signal, but has a frequency spectrum range of 0 -
1HZ.
The problem that I am facing is, I am getting very high values for
very low frequency reg
What is your sample rate, how long is your measurement time and what
window are you using? These are just few questions that would need
answers in order to help tracking your problem.
So it could be very helpful if you could post your VI with the actual
input data you are analyzing (saved as defau
Since your signal contains a lot of DC (approx. value = 1000), you may
consider removing some of it before computing your Power Spectrum. The
problem is to figure out what the exact dc value is and make sure you
do not remove part of the "interesting" signal. Unfortunately in your
case, as I mentio
I got to point out something here. The vertical axis unit for the time
domain signal is milliseconds,and not volts. I am a bit lost here,
would the term DC apply to our case here ? Let's we call it the DC
offset, can't we remove it by taking the mean of the raw data and then
subtracting the values
Well "DC" was the term used under the assumption that it is an
amplitude y-axis (DC = Direct Courant). It may not be the correct term
to use if the y-axis is in ms but as you say let's just call that
"dc".
Yes you can remove the "dc" by subtracting the mean value but by doing
this you "define" you
Here is what my work is all about. I am trying to develop a software
for Heart Rate Variability analysis. I am not sure if you are aware of
heart beat waveforms, they are bunch spikes, occuring at irregular
intervals. We have to do analysis on this waveform. How ? First we
have to create a plot cal
Well, I understand now that you are measuring a time "jitter" and that
your "offset" corresponds to the mean heart beat time of approx. 1000
ms. So again if you want to analyze the variation in frequency you
need to remove the "uninteresting dc".
The huge value you see at 0.0033 (that is the first
What you have said is really informative. Thanks a lot!
You suggested not using a window, but if I try without one, the
spectrum is crowded without any clear pattern showing up. I think not
removing the dc, was the problem why that high value for 0.0033 HZ
showed up. You talk about bins here, how
I would recommend you to read for example the "LabVIEW Analysis
Concepts" document that explains all the different concepts, "bin",
"averaging" etc...
You can access the document from your Desktop: Start>>Programs>>Nat.
Inst.>>LabVIEW **>>Search the LabVIEW Bookshelf
Select the "Measurement Manua
