Nyqusit Frequency

I am new to this subject...I have 250Khz signal sampled at
20MHz. How far can
lower the sampling frequency and still satisfy the nyquist
criterion for
such a signal. How is the nyquist frequency determined in
this case.
Thanks in advance for all your feedbacks.

NT
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ty-nyquist

Hi,

To sample a signal, the minimum sampling frequency is twice
that of the 
highest harmonic of the signal.

So if your 250khz tone is a pure sinewave, the lowest
sampling frequency 
would be 500khz.

The generally-accepted upper range of human hearing is
20khz, and CD's are 
recorded slightly above twice this frequency, at 44.1khz.

I can't get any more detailed about answering your
question.

This list is more specifically for writing plug-ins for the
open 
source audio editor Audacity, using a programming language
called Nyquist,
which can generate and process audio in Audacity.

David

-- 
David R. Sky
http://www.shell
world.net/~davidsky/


On Wed, 22 Aug 2007, nitin.abaqus wrote:

>
> I am new to this subject...I have 250Khz signal sampled
at 20MHz. How far can
> lower the sampling frequency and still satisfy the
nyquist criterion for
> such a signal. How is the nyquist frequency determined
in this case.
> Thanks in advance for all your feedbacks.
>
> NT
>

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ty-nyquist

Really off-topic, but there are two issues I like to
clarify.

Firstly, about the Nyquist frequency:

On Wed, 22 Aug 2007, nitin.abaqus wrote:
"I have 250Khz signal sampled at 20MHz."

" How is the nyquist frequency determined in this
case."

Nyquist frequency is not case dependent.

Secondly, about the signal itself:

"...satisfy the nyquist criterion for such a
signal."

Such a signal. What kind of signal? "250 kHz" does
not really describe
the form of the signal. I suspect it is not pure sine wave.
You don't
even explain if the 250 kHz means the frequency of the tone,
or the
maximum frequency that the signal can contain.


If there is a need to examine any signal in finer detail
(waveform
shape, harmonics), you cannot apply the Nyquist theorem. On
the other
hand, if you just need to measure the fundamental frequency
and/or
level of the signal, detect errors etc. then sampling rate =
f/2 is
fine.


-- 
Sami "Some-E" Jumppanen
sami.jumppanengmail.com
http://netti.nic.fi/~som
e-e/

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ty-nyquist

Hello,
 
Audio files are compressed by MP3. Changing sample rate in
preferences
will accomplish nothing and might foul things up. 

See the Dover reprint "Mathematical Foundations of
Information Theory"
by A. I Kninchin for more on the transmission of
information. 

My other reference is by Mickey Mouse. 

If a sine wave is sampled by rectangular pulses, and those
pulses are at
least twice the sine frequency; then the train of pulses can
be smoothed
by capacitors and resistors, such that the original sine
wave is
reproduced with reasonable accuracy. 

Professor Sniffy





On Thu, 23 Aug 2007 12:18:09 +0300, "Sami
Jumppanen"
<sami.jumppanengmail.com> said:
> Really off-topic, but there are two issues I like to
clarify.
> 
> Firstly, about the Nyquist frequency:
> 
> On Wed, 22 Aug 2007, nitin.abaqus wrote:
> "I have 250Khz signal sampled at 20MHz."
> 
> " How is the nyquist frequency determined in this
case."
> 
> Nyquist frequency is not case dependent.
> 
> Secondly, about the signal itself:
> 
> "...satisfy the nyquist criterion for such a
signal."
> 
> Such a signal. What kind of signal? "250 kHz"
does not really describe
> the form of the signal. I suspect it is not pure sine
wave. You don't
> even explain if the 250 kHz means the frequency of the
tone, or the
> maximum frequency that the signal can contain.
> 
> 
> If there is a need to examine any signal in finer
detail (waveform
> shape, harmonics), you cannot apply the Nyquist
theorem. On the other
> hand, if you just need to measure the fundamental
frequency and/or
> level of the signal, detect errors etc. then sampling
rate = f/2 is
> fine.
> 
> 
> -- 
> Sami "Some-E" Jumppanen
> sami.jumppanengmail.com
> http://netti.nic.fi/~som
e-e/
> 
>
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ty-nyquist
-- 
  paul beach
  sniffyravenfastmail.fm


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