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Hi All,

What is the utility of "demodulated noise"?  Why do DEMON processing?

I am working on acoustic signal processing applications involving rotating
machinery.  Once the carrier (generated by a rotating shaft) has been
demodulated what is significant about the remaining signal?  Might it
contain information about the source (i.e., the machinery) such as a
cavitation signature for the case of propellers on a vessels or perhaps
some other telltale trait?  If so, would these signals qualify as
noise???

How would a time vs frequency (waterfall) plot of the FFT'd data look
different from a plot for which noise demodulation was not performed?

Thanks,

Mikial

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On Mar 11, 11:59 pm, "Mikial Chubarov" <mikialchuba...@ieee.org>
wrote:
> Hi All,
>
> What is the utility of "demodulated noise"?  Why do DEMON processing?
>
> I am working on acoustic signal processing applications involving rotating
> machinery.  Once the carrier (generated by a rotating shaft) has been
> demodulated what is significant about the remaining signal?  Might it
> contain information about the source (i.e., the machinery) such as a
> cavitation signature for the case of propellers on a vessels or perhaps
> some other telltale trait?  If so, would these signals qualify as
> noise???
>
> How would a time vs frequency (waterfall) plot of the FFT'd data look
> different from a plot for which noise demodulation was not performed?
>
> Thanks,
>
> Mikial

The original DEMON process was intended to detect a broadband signal
(cavitation impulses) generated by a cyclical process (blade passage
near the keel). The signal processor performed narrowband analysis and
showed no indication of the impulses. So, a detection process was
performed (with a simple very low frequency DC removal) to produce the
envelope that was a narrowband process suitable for the processor. The
impulses were 'noise' with respect to a narrowband processor.

Machinery might produce similar signals from the passage of a broken
tooth or other mechanisms.

The DEMON process also works for conventional sidebands.

In the SONAR case, a band from 1 to 4 kHZ might be run through a
detector, DC removed, low pass filtered and desampled for analysis in
a band from a fraction to several Hertz. A waterfall of the 1-4 kHz
DEMON input band might show no signal related to the cavitation
source. The waterfall of the several Hertz wide DEMON output band
might show a strong tone at the blade passage rate. This process would
also detect conventional side bands within several Hertz of any
carrier in the 1-4 kHz band.

Dale B. Dalrymple
http://dbdimages.com

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Thank you Dale.

Mikial

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Dale wrote:
...
> Dale B. Dalrymple
> http://dbdimages.com

Hello Dale,

nice photos! Here in Switzerland, snowboarding season is drawing
close, and I haven't yet managed to get my board out of the cellar.
Your photos have motivated me to take one of the next days off from
work and enjoy the beautiful weather in the mountains.

Thanks :-)!

Regards,
Andor

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