signal signature

Discussion in 'General Electronics Chat' started by bug13, Aug 26, 2013.

  1. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
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    Hi guys

    How can I get a signature from a signal?

    Say I got a random signal which have a unique pattern or something, but different amplitude. How can I identify this signal?

    I have no idea what to google, or where to start with. I am hoping to get some pointer, or even better, an 101 example and explanation (if not too much to ask for).

    Thanks guys
     
  2. BillB3857

    Senior Member

    Feb 28, 2009
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    You may be able to use a digital oscilloscope set to trigger upon the event and see the pattern. Of course you would need to have some idea of the event duration in order to set up the horizontal time base, as well as the anticipated maximum amplitude in order to set the vertical sensitivity and trigger level.
     
  3. joeyd999

    AAC Fanatic!

    Jun 6, 2011
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    Google Fast Fourier Transform.
     
  4. wayneh

    Expert

    Sep 9, 2010
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    What sort of signal are we talking about? Whale songs? Dancing honeybees?

    I think you need a LOT of processing power, if you're trying to compare excerpts of "noise" to a database, to see if there is a signal hiding in the noise. But, processing is fairly cheap these days.

    I believe the record companies are doing something like this to detect copywritten material in Youtube videos and such.
     
  5. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
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    I am asking a general question, but I am interested in EMG signal, if you need one specify signal. Start with simple one if possible, just ignore the noise at the moment. I think I need to understand the basic concept before I can get any further.
     
  6. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    One way is to amplify and clip the signal so it becomes a simple on/off digital signal waveform, then compare the timings of the on/off periods.

    That is very easy to do if that is the only signal or the strongest signal, but won't be much help if there are many signals mixed together.
     
  7. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    You might consider Daubechies Wavelets or similar approach.
     
  8. WBahn

    Moderator

    Mar 31, 2012
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    One way is to use a matched filter, which is basically the same thing as using an autocorrelator. This has problems if the received signal is compressed or spread out in time compared to the reference signal.
     
  9. ScottWang

    Moderator

    Aug 23, 2012
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    If the amplitude of signal is regular as the video signal then you can using Op amp or comparator and to set a Vref to get the signal you want, if you only want to get the signature of signal, then you only need one comparator, if you want to get two signals then you can using two comparators to get the signature and the rest signals.
     
  10. wayneh

    Expert

    Sep 9, 2010
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    Interesting. I can see obvious application in biomedical prosthetics if you could sort out an EMG signal. (My daughter is a biomedical engineer.) I read the Wiki on EMG and found this useful information:

    "EMG signals are essentially made up of superimposed motor unit action potentials (MUAPs) from several motor units. For a thorough analysis, the measured EMG signals can be decomposed into their constituent MUAPs. MUAPs from different motor units tend to have different characteristic shapes, while MUAPs recorded by the same electrode from the same motor unit are typically similar. Notably MUAP size and shape depend on where the electrode is located with respect to the fibers and so can appear to be different if the electrode moves position. EMG decomposition is non-trivial, although many methods have been proposed."
     
  11. WBahn

    Moderator

    Mar 31, 2012
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    Huh?

    He's talking about something like EMG (electromyography) signals, not video signals. But even if he were looking for video signals with a certain signature, how is using one comparator going to tell him when Lucy is stomping the grapes?

    I might have a vague notion of what you are thinking of, but if so, then you are leaving out a LOT of conceptual information.
     
  12. ScottWang

    Moderator

    Aug 23, 2012
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    Hi, WBahn.
    I'm sorry, If what I said let you make misunderstanding, the meaning that I mentioned about the video, I'm not meant to he were looking for video signals, it just made an example to describe if the amplitude of signal is regular and not a random, if the amplitude is regular then it can be using comparator to seperate the signature from the signal, the important thing is the amplitude, if the signals is chaos, of course only using one or two comparators can't do that.
     
  13. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
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    Thanks guys, that's a lot for me to look into one by one, thanks for all the info and pointers.
     
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