From: Tim Wescott on
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
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
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
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
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?