Solving DSP problem
in [DSP]
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From: Tim Wescott on 18 Jan 2010 16:58 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. -- www.wescottdesign.com
From: Jerry Avins on 18 Jan 2010 17:50 Tim Wescott wrote: ... > 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. You would enjoy the popular works of Neil deGrasse Tyson. Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
From: Richard Owlett on 18 Jan 2010 19:05 Jerry Avins wrote: > Tim Wescott wrote: > > ... > >> 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. > > You would enjoy the popular works of Neil deGrasse Tyson. That name almost "rings a bell". Why? > > Jerry
From: Gordon Sande on 18 Jan 2010 20:30 On 2010-01-18 20:05:35 -0400, Richard Owlett <rowlett(a)pcnetinc.com> said: > Jerry Avins wrote: >> Tim Wescott wrote: >> >> ... >> >>> 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. >> >> You would enjoy the popular works of Neil deGrasse Tyson. > > That name almost "rings a bell". Why? He hosts NOVA ScienceNOW on PBS. He wears neat vests as well as being a serious scientist. Check him out on Wiki. Ask Google! > >> >> Jerry
From: Andor on 19 Jan 2010 02:06
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? |