Negative Group Delay ... again!

On Mar 7, 5:18&#4294967295;pm, Andor <andor.bari...@gmail.com> wrote:
> From a recent discussion here:
>
> > >if i could generate some coefficents that had a 'negative' group delay for
> > >a period of time, would you think that 'phase cloning' was new and
> > >intersting??
>
> > A time machine would be pretty revolutionary, yes.
>
> > Negative group delay means that the output appears before the input
> > arrives.
>
> Fascinating concept, isn't it? I was curious enough to dig into the
> topic for a while and write up what I found out. You can read about it
> here:
>
> http://www.dsprelated.com/showarticle/54.php
>
> Regards,
> Andor

thank you

Fig 6 was facinating...

Could you reproduce Fig 6 except start at T=0?

It would be interesting to see what happens at the very
(unpredictable) start of the input signal.

I'm going to build one of these and go to Wall Street  :-).
Too bad stock numbers are not bandlimted  :-(

Mark

On Mar 8, 2:55 pm, Rune Allnor <all...@tele.ntnu.no> wrote:
> On Mar 8, 3:43 pm, Oli Charlesworth <ca...@olifilth.co.uk> wrote:
>
> > On Mar 8, 2:01 pm, Rune Allnor <all...@tele.ntnu.no> wrote:
>
> > > On Mar 8, 2:38 pm, Oli Charlesworth <ca...@olifilth.co.uk> wrote:
>
> > > > I'm not sure it matters what the technique is?
>
> > > It does to me. A result derived with a known, well-udnerstood
> > > technique has a far greater impact than a unfamiliar, possibly
> > > novel technique applied to a tricky question.
>
> > Perhaps.
>
> Certainly. If a conclusion depends on using a novel method
> to do a standard computation, the first awkward questions
> will inevitably concern the soundness of this new method.
> It will only strengthen the conclusion if it can be demonstrated
> that the conclusion is independent of numerical methods used.
>
>
>
> > > > Surely all that
> > > > matters is that a discrete-time filter is derived that has the key
> > > > properties of its CT counterpart (approximately flat -ve group delay
> > > > over a region with approximately flat magnitude response).  The fact
> > > > that the overall response is roughly the same is merely an aesthetic
> > > > bonus.
>
> > > Wrong. If the claim applies to the CT cirquit, it is the CT
> > > cirquit which must be analyzed.
>
> > Not necessarily.  See further down...
>
> > > > How would you suggest performing the experiment in CT, short of
> > > > actually building the circuit?  Even circuit analysis tools have to
> > > > operate in discrete time.
>
> > > Derive and analyze the Laplace transform for the cirquit?
> > > All analytical, should be easy.
>
> > Yes, we could analyse via the Laplace domain by putting in a signal
> > with a known equation, and examining the output signal's equation.
>
> No. The LT describes the linear system regardless of
> input and output signals. If the LP is invalid, then
> the system is nonlinear and thus the concept of group
> delay is undefined.

Not sure I understand.  It's a given that the continuous-time system
is LTI, therefore we can apply the LT.  In what way would it be
invalid?


--
Oli