Negative Group Delay ... again!

Started by Andor March 7, 2008
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
On Mar 7, 5:18&#2013266080;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
Hello Andor, Very well written article. Hopefully this will put a lot of the seeming paradoxes associated with group delay to bed. The previous threads must have set a limit for their quantity. Whole books have been written on this subject as it is quite slippery. The D'enouement makes itself apparent when you try to trick mother nature and the predictability goes out the window. You can have fun by feeding this circuit's output back to its input and make a negative group delay oscillator - wouldn't that be odd? Good Job, Clay
On Fri, 7 Mar 2008 14:18:06 -0800 (PST), Andor
<andor.bariska@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
Nicely done! Gotta admit, I learned some things there, and the article is good enough that I do feel I understand the topic better. Kudos for including the code, too! But wouldn't it be impressive if I'd said that before the article was published? ;) Eric Jacobsen Minister of Algorithms Abineau Communications http://www.ericjacobsen.org
On Mar 7, 2:18 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
Very nice write-up Andor. Far from being an impossible time machine, it looks like any pole(s) inside the unit circle and much nearer than the canceling zero(s) could have a tiny frequency band with negative group delay. So what this says:
> > Negative group delay means that the output appears before the input > > arrives.
might be be better stated at this: A filter with negative group delay can produce the output before the input if the input has been on and continues on a highly predictable trajectory due to staying completely within a certain constrained bandwidth. No violation of causality becaues of the "if" clause. IMHO. YMMV. -- rhn A.T nicholson d.0.t C-o-M
On Mar 7, 11:18&#2013266080;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
Interesting piece. Just a couple of questions: - Why not use the BLT to transfor to discrete-time domain? I don't know Greg's stuff, I am familiar with the properties of the BLT. - Why analyze in discrete-time domain at all? Your results would have been seriously interesting if you could demonstrate similar effects in continuos-time domain; here they are amusing. - Why not use the impulse as test signal? You refer to 'some' who 'claim' that system with negative group delays are noncausal, as if you contest (or at least not support) such a view. I have made such claims. Your way of phrasing opens a whole new can of worms of semantic wars etc - why not demonstarte once and for all that systems with negative group delays exist and can be implemented in CT? (If that indeed is your claim, of course; I could not find out from the article what your stand on the issue is.) I would suggest the following: 1) Make a clear statement of the 'usual' views on the issue, your own opinions, and exactly what this article aims to demonstrate. 2) Compute the phase response of the CT system function and demonstrate that there is a negative group delay there. If you have the tools, I would also suggest you simulate the impulse response of that circuit in CT domain. 3) Use standard techniques in DT domain (BLT, Kronecker delta) and repeat your analysis. If all the results persist (system functions show negative group delays, anticausal behaviour) after such a re-work, I will consider to spend some time looking into your article in more detail. As the article stands, it only cretates confusion. A less benevolent reviewer than me might sugest that the instability caused by the truncated signal is caused by poles located outside the unit circle, and thus suggest that there is a fundamental flaw in the argument. As you know, if you can repeat the results using standard analysis tools and from multiple angles of attack, it will stop those sorts of argument at the outset. Rune
On Mar 7, 11:18=A0pm, 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
Interesting piece. Just a couple of questions: - Why not use the BLT to transfor to discrete-time domain? I don't know Greg's stuff, I am familiar with the properties of the BLT. - Why analyze in discrete-time domain at all? Your results would have been seriously interesting if you could demonstrate similar effects in continuos-time domain; here they are amusing. - Why not use the impulse as test signal? You refer to 'some' who 'claim' that system with negative group delays are noncausal, as if you contest (or at least not support) such a view. I have made such claims. Your way of phrasing opens a whole new can of worms of semantic wars etc - why not demonstarte once and for all that systems with negative group delays exist and can be implemented in CT? (If that indeed is your claim, of course; I could not find out from the article what your stand on the issue is.) I would suggest the following: 1) Make a clear statement of the 'usual' views on the issue, your own opinions, and exactly what this article aims to demonstrate. 2) Compute the phase response of the CT system function and demonstrate that there is a negative group delay there. If you have the tools, I would also suggest you simulate the impulse response of that circuit in CT domain. 3) Use standard techniques in DT domain (BLT, Kronecker delta) and repeat your analysis. If all the results persist (system functions show negative group delays, anticausal behaviour) after such a re-work, I will consider to spend some time looking into your article in more detail. As the article stands, it only cretates confusion. A less benevolent reviewer than me might sugest that the instability caused by the truncated signal is caused by poles located outside the unit circle, and thus suggest that there is a fundamental flaw in the argument. As you know, if you can repeat the results using standard analysis tools and from multiple angles of attack, it will stop those sorts of argument at the outset. Rune
On Mar 7, 11:18&#2013266080;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
Interesting piece. Just a couple of questions: - Why not use the BLT to transfor to discrete-time domain? I don't know Greg's stuff, I am familiar with the properties of the BLT. - Why analyze in discrete-time domain at all? Your results would have been seriously interesting if you could demonstrate similar effects in continuos-time domain; here they are amusing. - Why not use the impulse as test signal? You refer to 'some' who 'claim' that system with negative group delays are noncausal, as if you contest (or at least not support) such a view. I have made such claims. Your way of phrasing opens a whole new can of worms of semantic wars etc - why not demonstarte once and for all that systems with negative group delays exist and can be implemented in CT? (If that indeed is your claim, of course; I could not find out from the article what your stand on the issue is.) I would suggest the following: 1) Make a clear statement of the 'usual' views on the issue, your own opinions, and exactly what this article aims to demonstrate. 2) Compute the phase response of the CT system function and demonstrate that there is a negative group delay there. If you have the tools, I would also suggest you simulate the impulse response of that circuit in CT domain. 3) Use standard techniques in DT domain (BLT, Kronecker delta) and repeat your analysis. If all the results persist (system functions show negative group delays, anticausal behaviour) after such a re-work, I will consider to spend some time looking into your article in more detail. As the article stands, it only cretates confusion. A less benevolent reviewer than me might sugest that the instability caused by the truncated signal is caused by poles located outside the unit circle, and thus suggest that there is a fundamental flaw in the argument. As you know, if you can repeat the results using standard analysis tools and from multiple angles of attack, it will stop those sorts of argument at the outset. Rune
On Mar 7, 11:18=A0pm, 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
Interesting piece. Just a couple of questions: - Why not use the BLT to transfor to discrete-time domain? I don't know Greg's stuff, I am familiar with the properties of the BLT. - Why analyze in discrete-time domain at all? Your results would have been seriously interesting if you could demonstrate similar effects in continuos-time domain; here they are amusing. - Why not use the impulse as test signal? You refer to 'some' who 'claim' that system with negative group delays are noncausal, as if you contest (or at least not support) such a view. I have made such claims. Your way of phrasing opens a whole new can of worms of semantic wars etc - why not demonstarte once and for all that systems with negative group delays exist and can be implemented in CT? (If that indeed is your claim, of course; I could not find out from the article what your stand on the issue is.) I would suggest the following: 1) Make a clear statement of the 'usual' views on the issue, your own opinions, and exactly what this article aims to demonstrate. 2) Compute the phase response of the CT system function and demonstrate that there is a negative group delay there. If you have the tools, I would also suggest you simulate the impulse response of that circuit in CT domain. 3) Use standard techniques in DT domain (BLT, Kronecker delta) and repeat your analysis. If all the results persist (system functions show negative group delays, anticausal behaviour) after such a re-work, I will consider to spend some time looking into your article in more detail. As the article stands, it only cretates confusion. A less benevolent reviewer than me might sugest that the instability caused by the truncated signal is caused by poles located outside the unit circle, and thus suggest that there is a fundamental flaw in the argument. As you know, if you can repeat the results using standard analysis tools and from multiple angles of attack, it will stop those sorts of argument at the outset. Rune
On Mar 7, 11:18=A0pm, 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
Interesting piece. Just a couple of questions: - Why not use the BLT to transfor to discrete-time domain? I don't know Greg's stuff, I am familiar with the properties of the BLT. - Why analyze in discrete-time domain at all? Your results would have been seriously interesting if you could demonstrate similar effects in continuos-time domain; here they are amusing. - Why not use the impulse as test signal? You refer to 'some' who 'claim' that system with negative group delays are noncausal, as if you contest (or at least not support) such a view. I have made such claims. Your way of phrasing opens a whole new can of worms of semantic wars etc - why not demonstarte once and for all that systems with negative group delays exist and can be implemented in CT? (If that indeed is your claim, of course; I could not find out from the article what your stand on the issue is.) I would suggest the following: 1) Make a clear statement of the 'usual' views on the issue, your own opinions, and exactly what this article aims to demonstrate. 2) Compute the phase response of the CT system function and demonstrate that there is a negative group delay there. If you have the tools, I would also suggest you simulate the impulse response of that circuit in CT domain. 3) Use standard techniques in DT domain (BLT, Kronecker delta) and repeat your analysis. If all the results persist (system functions show negative group delays, anticausal behaviour) after such a re-work, I will consider to spend some time looking into your article in more detail. As the article stands, it only cretates confusion. A less benevolent reviewer than me might sugest that the instability caused by the truncated signal is caused by poles located outside the unit circle, and thus suggest that there is a fundamental flaw in the argument. As you know, if you can repeat the results using standard analysis tools and from multiple angles of attack, it will stop those sorts of argument at the outset. Rune
On Mar 7, 11:18&#2013266080;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
Interesting piece. Just a couple of questions: - Why not use the BLT to transfor to discrete-time domain? I don't know Greg's stuff, I am familiar with the properties of the BLT. - Why analyze in discrete-time domain at all? Your results would have been seriously interesting if you could demonstrate similar effects in continuos-time domain; here they are amusing. - Why not use the impulse as test signal? You refer to 'some' who 'claim' that system with negative group delays are noncausal, as if you contest (or at least not support) such a view. I have made such claims. Your way of phrasing opens a whole new can of worms of semantic wars etc - why not demonstarte once and for all that systems with negative group delays exist and can be implemented in CT? (If that indeed is your claim, of course; I could not find out from the article what your stand on the issue is.) I would suggest the following: 1) Make a clear statement of the 'usual' views on the issue, your own opinions, and exactly what this article aims to demonstrate. 2) Compute the phase response of the CT system function and demonstrate that there is a negative group delay there. If you have the tools, I would also suggest you simulate the impulse response of that circuit in CT domain. 3) Use standard techniques in DT domain (BLT, Kronecker delta) and repeat your analysis. If all the results persist (system functions show negative group delays, anticausal behaviour) after such a re-work, I will consider to spend some time looking into your article in more detail. As the article stands, it only cretates confusion. A less benevolent reviewer than me might sugest that the instability caused by the truncated signal is caused by poles located outside the unit circle, and thus suggest that there is a fundamental flaw in the argument. As you know, if you can repeat the results using standard analysis tools and from multiple angles of attack, it will stop those sorts of argument at the outset. Rune