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HELP NEEDED: Understanding wavelet transform

Started by Paulina7m May 11, 2007
Hi, 
I've been trying to learn about DWT for quite a while now.
Still, I have some simple questions, which my searches on Google weren't
able to answer. Thank you in advance for your answers.

1. When decomposing a signal, using wavelet toolbox in matlab, what are
the axis?  Frequency over time? Or scale over time?

2. What does scale mean, if it's say 0.2, or 0.5. I don't see the relation
with frequency. I know it's the inverse of frequency, so is frequency =
1/0.2, when scale shows 0.2 in any of the approximations?

3. If scale reaches only positive 0.2, but not negative 0.2, what does it
mean? What does negative frequency mean here?

4. How exactly do I tell from the scale vs time plot , at what time which
frequency occured? (or what frequencies occured at what time intervals).
If the line is very close to scale 0, is the frequency equal to 0?

5. Please explain how do I choose a suitable decomposition level. Why it's
not a good idea to always use maximum decomposition level provided (say,
12, as in matlab's wav toolbox)? 

6. What is a threshold in DWT? How is it calculated? (I'm not going to
look in the math behind it, I'd like to have more of a general idea)

Thank you again for your help. 
If you can only answer 1 or 2 questions, that's fine as well.







_____________________________________
Do you know a company who employs DSP engineers?  
Is it already listed at http://dsprelated.com/employers.php ?
You are all professionals, 
I really need your help with the questions above.
One sentence answer will do too!

_____________________________________
Do you know a company who employs DSP engineers?  
Is it already listed at http://dsprelated.com/employers.php ?
On May 12, 8:28 am, "Paulina7m" <paulin...@yahoo.ca> wrote:
> You are all professionals,
How do you know that? :-)
> I really need your help with the questions above. > One sentence answer will do too!
Paulina, I am going to guess that the reason you did not get a response is because from reading your question, what you need is to learn what a wavelet transform is about. You are jumping well ahead into applying it to something you don't even tell us about. How can you expect quick help then? Further, a lot of your questions are answered in the documentation for the Matlab Wavelets Toolbox. Have you read it? I know for sure that they have basic tutorials that answer most of your questions here. In case you are not able to find it, here it is: http://www.mathworks.com/access/helpdesk/help/toolbox/wavelet/ Julius