From: Jerry Avins on 3 Dec 2007 12:04
Greg Berchin wrote:
> On Dec 2, 1:23 pm, Vladimir Vassilevsky <antispam_bo...(a)hotmail.com>
>> What if you integrate the signal in the two dimensions per revolution
>> and per half revolution?
> Hmmm; that's got me thinking. The fundamental and odd harmonics of
> the combined signal MUST come from the 1-per phenomenon. So this is
> really a matter of separating the even harmonics of the 1-per from the
> entirety of the 2-per.
> Even harmonics are generated by asymmetrical waveforms (asymmetry
> above and below the zero-amplitude line).
> Odd harmonics are generated by symmetrical waveforms.
> There's got to be a way to separate the symmetrical portions of the
> waveform from the asymmetrical portions of the waveform -- much like
> decomposing a waveform into its even- and odd-symmetric parts.
Again, this assumes that the two-per anomaly is "balanced". If it sounds
like tik-tik-pause, tik-tik-pause, the harmonic structure will be richer.
Engineering is the art of making what you want from things you can get.
From: Greg Berchin on 3 Dec 2007 12:53
On Dec 3, 12:04 pm, Jerry Avins <j...(a)ieee.org> wrote:
> Again, this assumes that the two-per anomaly is "balanced". If it sounds
> like tik-tik-pause, tik-tik-pause, the harmonic structure will be richer.
Good point. If the "tiks" are close enough together, they start to
look like a double-tik event that occurs once per revolution instead
of two single-tik events.
From: Ron N. on 3 Dec 2007 15:16
On Dec 2, 11:53 pm, "mnentwig" <mnent...(a)elisanet.fi> wrote:
> I would take a full number of cycles (!) of the signal and FFT it. Then
> notch out the spectral line corresponding to the fundamental, IFFT back to
> time domain, and you've got the double-frequency anomaly.
That assumes that the periodic phenomena has significant
(or any) energy in the fundamental frequency bin. Lot's of
interesting phenomena have a (nearly) missing fundamental
sinusoidal component. The interesting parts might all be
in the harmonics and perhaps the phase relationships between
such. But how does one go about separating out the even
multiple harmonics of the "once per" event from the spectra
of the "twice per" event plus all of its harmonics?
But the fact the Greg can hear two ticks and one thump (or
something like that) in the time/angular domain says that
the impulse responses might be at least partially separable
in that domain.
rhn A.T nicholson d.0.t C-o-M