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Basic Questions??

Started by Jamie May 3, 2006
Hello to all

I am an Engineering student and in my Viva Exam we were asked some
questions which are as follows::

(1). How to acquire or sample an arbitrary signal such that Aliasing is
completely avoided ??We dont know anything about the Input.

(2). How can we generate Impulse Waveform from our computer so that we
can use those impulse waveform in our DSP Hardware for doping an
Impulse response analysis.??

(3). Is there any ON Line Digital Filters present in the world??

(4). Can we have AntiAliasing Digital Filters??If yes/No Why??

Could anybody please tell me how to answer these questions??Please
reply.

With Regards
Jamie

One more Question.....

(5) If we have a 10Khz Processor and DAQ Card which samples at
100Khz/Samples......Can we have such configuration ????

I have these answers in my mind right now. But they can be discussed

(1). We use an anti-aliasing filter. We are limited by the hardware
sampling rate and we will put an anti-aliasing filter before the
sampler and hence get an arbitary signal.

(2). As DSP and computer both are in digital domain, so we put a one
followed by zeros.

(3). What do you mean by ON-line?? The transmit filters,
echo-cancellers, sample rate converters, digital down converters use
digital fitlers.

(4) We can have digital filters for anti-aliasing when we do resampling
in digital domain. But if you think that analog anti-aliasing filter
can be replaced by digital after the sampler, then we cannot have a
digital anti-alaising fitler.

Jamie wrote:
> Hello to all > > I am an Engineering student and in my Viva Exam we were asked some > questions which are as follows:: > > (1). How to acquire or sample an arbitrary signal such that Aliasing is > completely avoided ??We dont know anything about the Input. > > (2). How can we generate Impulse Waveform from our computer so that we > can use those impulse waveform in our DSP Hardware for doping an > Impulse response analysis.?? > > (3). Is there any ON Line Digital Filters present in the world?? > > (4). Can we have AntiAliasing Digital Filters??If yes/No Why?? > > Could anybody please tell me how to answer these questions??Please > reply.
People here don't give away answers to homework. Rune
"mobi" <mobien@gmail.com> wrote in message
news:1146655522.379792.202490@y43g2000cwc.googlegroups.com...
> I have these answers in my mind right now. But they can be discussed > > (1). We use an anti-aliasing filter. We are limited by the hardware > sampling rate and we will put an anti-aliasing filter before the > sampler and hence get an arbitary signal. > > (2). As DSP and computer both are in digital domain, so we put a one > followed by zeros. > > (3). What do you mean by ON-line?? The transmit filters, > echo-cancellers, sample rate converters, digital down converters use > digital fitlers. > > (4) We can have digital filters for anti-aliasing when we do resampling > in digital domain. But if you think that analog anti-aliasing filter > can be replaced by digital after the sampler, then we cannot have a > digital anti-alaising fitler.
"mobi" <mobien@gmail.com> wrote in message
news:1146655522.379792.202490@y43g2000cwc.googlegroups.com...

> (4) We can have digital filters for anti-aliasing when we do resampling > in digital domain. But if you think that analog anti-aliasing filter > can be replaced by digital after the sampler, then we cannot have a > digital anti-alaising fitler.
It is possible to sample under the nyquist frequency and still represent the actual signal - without pre-filtering. What is needed are a number channels - sampling at different frequencies - selecting - for instance - three channels sampling at well chosen frequencies wrt to the system frequency up to 2000 times the maximum sampling rate can be detected in the signal - and aliasing can be removed simply.
Setanta wrote:
> "mobi" <mobien@gmail.com> wrote in message > news:1146655522.379792.202490@y43g2000cwc.googlegroups.com... > > >>(4) We can have digital filters for anti-aliasing when we do resampling >>in digital domain. But if you think that analog anti-aliasing filter >>can be replaced by digital after the sampler, then we cannot have a >>digital anti-alaising fitler. > > > > It is possible to sample under the nyquist frequency and still represent the > actual signal - without pre-filtering. > What is needed are a number channels - sampling at different frequencies - > selecting - for instance - three channels sampling at well chosen > frequencies wrt to the system frequency up to 2000 times the maximum > sampling rate can be detected in the signal - and aliasing can be removed > simply.
Please tell me more. Jerry -- Engineering is the art of making what you want from things you can get. &#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;
Setanta wrote:
> "mobi" <mobien@gmail.com> wrote in message > news:1146655522.379792.202490@y43g2000cwc.googlegroups.com... > >> (4) We can have digital filters for anti-aliasing when we do resampling >> in digital domain. But if you think that analog anti-aliasing filter >> can be replaced by digital after the sampler, then we cannot have a >> digital anti-alaising fitler. > > > It is possible to sample under the nyquist frequency and still represent the > actual signal - without pre-filtering. > What is needed are a number channels - sampling at different frequencies - > selecting - for instance - three channels sampling at well chosen > frequencies wrt to the system frequency up to 2000 times the maximum > sampling rate can be detected in the signal - and aliasing can be removed > simply.
Note the "without pre-filtering" part. This also means the sampling gate must be very narrow, consistent with sampling the full bandwidth at the Nyquist rate. Many defence applications are based on this kind of multi rate sampling. The sampling rates need to be carefully chosen for best effect. Relatively prime number tend to work well. Steve
"Jerry Avins" <jya@ieee.org> wrote in message
news:bcydnd-NI9KZ78TZnZ2dnUVZ_v-dnZ2d@rcn.net...
> Setanta wrote: > > "mobi" <mobien@gmail.com> wrote in message > > news:1146655522.379792.202490@y43g2000cwc.googlegroups.com... > > > > > >>(4) We can have digital filters for anti-aliasing when we do resampling > >>in digital domain. But if you think that analog anti-aliasing filter > >>can be replaced by digital after the sampler, then we cannot have a > >>digital anti-alaising fitler. > > > > > > > > It is possible to sample under the nyquist frequency and still represent
the
> > actual signal - without pre-filtering. > > What is needed are a number channels - sampling at different
frequencies -
> > selecting - for instance - three channels sampling at well chosen > > frequencies wrt to the system frequency up to 2000 times the maximum > > sampling rate can be detected in the signal - and aliasing can be
removed
> > simply. > > Please tell me more. > > Jerry > -- > Engineering is the art of making what you want from things you can get. > &#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;
It is difficult to illiterate these ideas here in this arena If you want to no more check out a paper in 'Sound & Vibration Journal' Called Nyquist-overcoming the limitations R.F. McLeana,*, S.H. Alsopa, J.S. Flemingb HTH Kieran &#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;
Setanta wrote:

   ...

> It is difficult to illiterate these ideas here in this arena > > If you want to no more check out a paper in 'Sound & Vibration Journal' > > Called > > Nyquist-overcoming the limitations > > R.F. McLeana,*, S.H. Alsopa, J.S. Flemingb > > > > HTH > > Kieran
The Nyquist criterion applies not to absolute frequency, but to bandwidth. If its true meaning is misconstrued, then it is easy to improve in the unnecessarily restrictive limit. Is that what the paper describes? Are the paper's authors perhaps McLean, Alsop, and Fleming? Jerry -- Engineering is the art of making what you want from things you can get. &#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;