Luiz Carlos wrote:>> Luis Carlos, >> >> Nor are all bandlimited signals periodic..... >> >> Fred > > Hi Fred, > > Can you give me an example? > > Luiz Carlos.For instance, sin(t) + sin(Pi*t) is only pseudo-periodic because the frequency ratio is irrational. Martin
Fast response filter?
Started by ●January 15, 2004
Reply by ●January 22, 20042004-01-22
Reply by ●January 22, 20042004-01-22
"Jerry Avins" <jya@ieee.org> wrote in message news:400ff423$0$3062$61fed72c@news.rcn.com...> Fred Marshall wrote: > > > "Jerry Avins" <jya@ieee.org> wrote in message > > news:400eb4e1$0$2440$61fed72c@news.rcn.com... > > > > > > > >>......Otherwise, when striking a bell, you would get > >>radio interference, illumination, and X-rays. > > > > > > Jerry .... how in the world .... ???? > > > > Or, did you have some transformation of energy mechanism in mind thatisn't> > obvious. > > > > Were you referring to heat -> IR -> electromagnetic radiation? > > > > Otherwise, the model generally stays focused on mechanical energy in the > > case of a bell and the heat is neglected. Either way bandwidth hasnothing> > to do with it. Well .... unless there's some mechanism in going to heat/> > IR that somehow supports the creation of infinite bandwidths. > > > > Yeah, I know that supports the point of it being "real". But theexample> > seems to jump from one type of energy to another without justification. > > > > I have the feeling that I'm missing something but, as one might expect, > > don't know what it is! > > > > Fred > > I did sort of leave something out. (Big time!) I was thinking of eddy > currents in the moving metal caused by the earth's magnetic field, but > my mind skipped that paragraph. A steel guitar string won't do very well > unless the ends are shorted.Jerry, But doesn't the possible permanent deformation of either the bell or the hammer limit the bandwidth of the excitation? :-) If we assume that there is *none* because the elastic limit of both isn't exceeded, then aren't the eddy currents subject to distributed inductance and capacitance of the structure - and therefore limited in bandwidth? Oh! I get it, this was a troll to prove your oft made point about things being real, right? It really does. Peter Kootsookos mentioned a Slepian paper "On Bandwidth". Sounds interesting. Fred
Reply by ●January 22, 20042004-01-22
"Martin Eisenberg" <martin.eisenbergNOS@PAMudo.edu> wrote in message news:1074793175.607479@ostenberg.wh.uni-dortmund.de...> Luiz Carlos wrote: > > >> Luis Carlos, > >> > >> Nor are all bandlimited signals periodic..... > >> > >> Fred > > > > Hi Fred, > > > > Can you give me an example? > > > > Luiz Carlos. > > For instance, sin(t) + sin(Pi*t) is only pseudo-periodic because the > frequency ratio is irrational.Yes, that's a good example. I don't know what "pseudo-periodic" means .... Fred
Reply by ●January 22, 20042004-01-22
Jerry Avins wrote:> > Stephan Sprenger once wrote here (when that was still his name),What's his name now? Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein
Reply by ●January 22, 20042004-01-22
Bob Cain wrote:> > Jerry Avins wrote: > >>Stephan Sprenger once wrote here (when that was still his name), > > > What's his name now? > > > BobHe is now Stephan Bernsee. He married and took his wife's surname. No hyphen: he went R.B-J. one further. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●January 23, 20042004-01-23
On Thu, 22 Jan 2004 09:53:18 -0600, jim <"N0sp"@m.sjedging@mwt.net> wrote:> > >Allan Herriman wrote: >> >> >> How do you know you *don't* get radio interference, illumination and >> X-rays when you strike a bell? Maybe they're just at a really low >> level, too low for you to detect. > >What if you just pushed the bell with your finger? What if the bell were >made of marshmellows? Would you still expect the frquency response to go >to infinity? > Under what conditions does striking a bell become mathematically >perfect?I think you missed my point. (Jerry got it though.) Mathematical zero - the thing is exactly zero. Engineering zero - the thing is less than the noise floor. No analog filter has (or can have) infinite attenuation in its stopband over a finite range of frequencies (except if the attenuation is infinite for all frequencies), and no time-limited analog signal can have zero power over any finite range of frequencies (except if the signal is zero for all time). So, push the marshmallow bell with your finger and get a non-zero amount of X-rays. ... but that's using the mathematical definition of zero. In the engineering sense (and common sense!), you don't get anything at all (except a sticky finger). Regards, Allan.
Reply by ●January 23, 20042004-01-23
> For instance, sin(t) + sin(Pi*t) is only pseudo-periodic because the > frequency ratio is irrational. > > > MartinMartin, I din't like this one! It is periodic, it has an infinite period! If you say infinite period is not allowed, I'll say you can't generate sin(t)+sin(Pi*t), because you need infinite precision to generate it. If not, you'll have a finite period.> You needn't look far: excite a filter with noise. > > JerryJerry, I want the mathematical formula for this noise (or pseudo-noise). Not statistical parameters! Ok, I know this is not very much practical, but I think it interestesting! Luiz Carlos
Reply by ●January 23, 20042004-01-23
Martin, Somebody here said: sin(x)/x. (Now obvious!) So, I'll ask for something a little bit different: I want an example for a causal signal that has bandlimited spectrum. Luiz Carlos.
Reply by ●January 23, 20042004-01-23
Allan Herriman wrote:> > On Thu, 22 Jan 2004 09:53:18 -0600, jim <"N0sp"@m.sjedging@mwt.net> > wrote: > > > > > > >Allan Herriman wrote: > >> > >> > >> How do you know you *don't* get radio interference, illumination and > >> X-rays when you strike a bell? Maybe they're just at a really low > >> level, too low for you to detect. > > > >What if you just pushed the bell with your finger? What if the bell were > >made of marshmellows? Would you still expect the frquency response to go > >to infinity? > > Under what conditions does striking a bell become mathematically > >perfect? > > I think you missed my point. (Jerry got it though.) >Yes, I got the point. But, by your own admition, your assertions are based only on faith since there is no measurable proof. Anyway, an ideal impulse should have a flat response for all frequencies.> Mathematical zero - the thing is exactly zero. > Engineering zero - the thing is less than the noise floor. > > No analog filter has (or can have) infinite attenuation in its > stopband over a finite range of frequencies (except if the attenuation > is infinite for all frequencies), and no time-limited analog signal > can have zero power over any finite range of frequencies (except if > the signal is zero for all time). > > So, push the marshmallow bell with your finger and get a non-zero > amount of X-rays. > > ... but that's using the mathematical definition of zero. > > In the engineering sense (and common sense!), you don't get anything > at all (except a sticky finger). > > Regards, > Allan.-----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =-----
Reply by ●January 23, 20042004-01-23
In article <r58110dsd1gqv9avbb9qun77nksduqstt9@4ax.com>, Allan Herriman <allan.herriman.hates.spam@ctam.com.au.invalid> wrote:>Mathematical zero - the thing is exactly zero. >Engineering zero - the thing is less than the noise floor.Except that things below the noise floor can sometimes be measured, given enough time. However there is also: quantum zero - the thing is smaller than Planck's constant / 4 * pi where the mathematical model is no longer correct. IMHO. YMMV. -- Ron Nicholson rhn AT nicholson DOT com http://www.nicholson.com/rhn/ #include <canonical.disclaimer> // only my own opinions, etc.
