Solving DSP problem
in [DSP]
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From: Jerry Avins on 21 Jan 2010 03:26 Andor wrote: ... > Unfortunately, I don't know Gilligan. Wikipedia has an article about a > sitcom called Gilligan's Island, which I guess you are refering to. > Sounds like an older version of "Lost" ... My kids used to watch Gilligan's Island, and I overheard a bit: it's supposed to be comedy (and occasionally is). I'v never watches an episode of Lost, but from the little I've seen, any comedy is accidental. Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
From: Rune Allnor on 21 Jan 2010 04:27 On 19 Jan, 19:45, Tim Wescott <t...(a)seemywebsite.com> wrote: > On Mon, 18 Jan 2010 23:06:30 -0800, Andor wrote: > > On 18 Jan., 22:58, Tim Wescott <t...(a)seemywebsite.com> wrote: > >> On Mon, 18 Jan 2010 15:51:21 -0500, Jerry Avins wrote: > >> > Tim Wescott wrote: > >> >> On Mon, 18 Jan 2010 13:40:37 -0500, Jerry Avins wrote: > > >> >>> Tim Wescott wrote: > >> >>>> On Mon, 18 Jan 2010 09:25:50 -0600, Richello wrote: > > >> >>>>> Dear Sir, > > >> >>>>> Could you please help me to solve this or give me hints to do so? > > >> >>>>> An analogue signal x(t)=10cos(500Ït) is sampled at 0, T,2T, .... > >> >>>>> with T=1ms. > > >> >>>>> I want to find a cosine y(t), whose frequency is as close as > >> >>>>> possible to that of x(t), which when sampled with T=1ms yields > >> >>>>> the same sample values as x(t). how can I get the equation of > >> >>>>> y(t)? .. then  if x(nT) were the input to a D/A converter, > >> >>>>> followed by a low-pass smoothing filter, why would the output be > >> >>>>> x(t) and not y(t) ? > >> >>>> 1:  The solution as you state the problem is trivial: y(t) = x(t). > >> >>>>  I assume you mean the frequency should be close to but different. > > >> >>>> 2:  Have you asked your prof? > > >> >>>> 3:  Read this:  http://www.wescottdesign.com/articles/Sampling/ > >> >>>> sampling.html.  Skip down to the part about aliasing. > >> >>> First, fix the link: > >> >>>http://www.wescottdesign.com/articles/Sampling/sampling.html > > >> >>> I'm puzzled by Tim's reference to aliasing. The frequency is 250 Hz > >> >>> and the sample rate is 1000 Hz. > > >> >>> Jerry > > >> >> He's asking for a continuous-time signal (presumably not identical > >> >> to the given one) that gives the same discrete-time signal after > >> >> sampling. > >> >>  That sounds like aliasing to me. > > >> >> It sounds like a _homework problem_ about aliasing.  One I might > >> >> write were I teaching a signal processing course, I might add. > > >> > Got it. I would have worded it differently, though. > > >> I would have worded it differently, too.  A set of homework problems > >> that doesn't contain at least one veiled reference to Bart Simpson, > >> Batman, Diogenes, Gilligan, or some other major philosopher is a minor > >> failure, IMHO. > > > Cool - can you reword the OPs problem in that vein? > > I've got it: Brilliant! Rune
From: glen herrmannsfeldt on 21 Jan 2010 05:02 Jerry Avins <jya(a)ieee.org> wrote: (snip) > My kids used to watch Gilligan's Island, and I overheard a bit: it's > supposed to be comedy (and occasionally is). I'v never watches an > episode of Lost, but from the little I've seen, any comedy is accidental. I still remember Gilligan's Island as the first show we watched after getting a UHF converter for our (black and white) TV. There are a few things that I still remember from watching it many years ago, including methyl salicylic acid, when the professor was asked to say something scientific. (To impress someone else.) He then explains that it is the chemical name for aspirin. -- glen
From: Tim Wescott on 21 Jan 2010 10:14 On Wed, 20 Jan 2010 23:55:54 -0800, Andor wrote: > On 19 Jan., 19:45, Tim Wescott <t...(a)seemywebsite.com> wrote: >> On Mon, 18 Jan 2010 23:06:30 -0800, Andor wrote: >> > On 18 Jan., 22:58, Tim Wescott <t...(a)seemywebsite.com> wrote: >> >> On Mon, 18 Jan 2010 15:51:21 -0500, Jerry Avins wrote: >> >> > Tim Wescott wrote: >> >> >> On Mon, 18 Jan 2010 13:40:37 -0500, Jerry Avins wrote: >> >> >> >>> Tim Wescott wrote: >> >> >>>> On Mon, 18 Jan 2010 09:25:50 -0600, Richello wrote: >> >> >> >>>>> Dear Sir, >> >> >> >>>>> Could you please help me to solve this or give me hints to do >> >> >>>>> so? >> >> >> >>>>> An analogue signal x(t)=10cos(500πt) is sampled at 0, T,2T, >> >> >>>>> .... with T=1ms. >> >> >> >>>>> I want to find a cosine y(t), whose frequency is as close as >> >> >>>>> possible to that of x(t), which when sampled with T=1ms yields >> >> >>>>> the same sample values as x(t). how can I get the equation of >> >> >>>>> y(t)? .. then if x(nT) were the input to a D/A converter, >> >> >>>>> followed by a low-pass smoothing filter, why would the output >> >> >>>>> be x(t) and not y(t) ? >> >> >>>> 1: The solution as you state the problem is trivial: y(t) = >> >> >>>> x(t). >> >> >>>> I assume you mean the frequency should be close to but >> >> >>>> different. >> >> >> >>>> 2: Have you asked your prof? >> >> >> >>>> 3: Read this: http://www.wescottdesign.com/articles/Sampling/ >> >> >>>> sampling.html. Skip down to the part about aliasing. >> >> >>> First, fix the link: >> >> >>>http://www.wescottdesign.com/articles/Sampling/sampling.html >> >> >> >>> I'm puzzled by Tim's reference to aliasing. The frequency is 250 >> >> >>> Hz and the sample rate is 1000 Hz. >> >> >> >>> Jerry >> >> >> >> He's asking for a continuous-time signal (presumably not >> >> >> identical to the given one) that gives the same discrete-time >> >> >> signal after sampling. >> >> >> That sounds like aliasing to me. >> >> >> >> It sounds like a _homework problem_ about aliasing. One I might >> >> >> write were I teaching a signal processing course, I might add. >> >> >> > Got it. I would have worded it differently, though. >> >> >> I would have worded it differently, too. A set of homework problems >> >> that doesn't contain at least one veiled reference to Bart Simpson, >> >> Batman, Diogenes, Gilligan, or some other major philosopher is a >> >> minor failure, IMHO. >> >> > Cool - can you reword the OPs problem in that vein? >> >> I've got it: >> >> Gilligan has sprung a net trap set by natives from the next island >> over; the trap is hung from a tall tree branch, and Gilligan is >> swinging over a small clearing with a period of oscillation of 5 >> seconds (0.2Hz). >> >> The Skipper has also been captured and blindfolded and is being held >> nearby. Every two seconds exactly he manages to pull off the blindfold >> and see Gilligan, but his captors immediately replace the blindfold >> each time. >> >> What is the _closest_ (but not identical) period of oscillation at >> which Gilligan could be swinging such that the Skipper would see >> exactly the same period of oscillation given how often he pulls off his >> blindfold? >> >> For extra credit: >> >> The Skipper escapes, and runs to the Professor to explain Gilligan's >> dilemma (including the timing, of course). The Professor (having taken >> signal processing courses along with everything else), knows that there >> are two likely periods to the swing, and thus knows the two possible >> lengths of the rope from which Gilligan is suspended (he ignores the >> mass of the rope and assumes the tree is infinitely rigid). >> >> Assuming that the professor gets his math right, how long are his two >> calculated rope lengths? > > :-) > > Unfortunately, I don't know Gilligan. Wikipedia has an article about a > sitcom called Gilligan's Island, which I guess you are refering to. > Sounds like an older version of "Lost" ... Well, perhaps if you take all the 'spooky wierd' parts of "Lost" and replace them with 'goofy funny'. "Gilligan's Island" was basic slapstick comedy, set up by the idea that you had seven random US citizens shipwrecked on a Pacific island, driven forward by the fact that the characters that considered themselves in charge and competent weren't, and leavened by the presence of Gilligan, who was a classic clown. -- www.wescottdesign.com
From: Jerry Avins on 21 Jan 2010 11:06
glen herrmannsfeldt wrote: > Jerry Avins <jya(a)ieee.org> wrote: > > (snip) >> My kids used to watch Gilligan's Island, and I overheard a bit: it's >> supposed to be comedy (and occasionally is). I'v never watches an >> episode of Lost, but from the little I've seen, any comedy is accidental. > > I still remember Gilligan's Island as the first show we watched > after getting a UHF converter for our (black and white) TV. > > There are a few things that I still remember from watching it > many years ago, including methyl salicylic acid, when the professor > was asked to say something scientific. (To impress someone else.) > He then explains that it is the chemical name for aspirin. Nitpick: acetylsalicylic acid. I remember an ad for an "Amazing New Analgesic Discovery!": sodium acetylsalicylate. The FTC had the ad pulled. Jerry -- Engineering is the art of making what you want from things you can get. ����������������������������������������������������������������������� |