Nyqusit Frequency

[nitin.abaqus]

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

[David R. Sky]

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.shellworld.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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[Sami Jumppanen]

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.jumppanen@...
http://netti.nic.fi/~some-e/

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[paul beach-2]

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.jumppanen@...> 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.jumppanen@...
> http://netti.nic.fi/~some-e/
>
> -------------------------------------------------------------------------
> This SF.net email is sponsored by: Splunk Inc.
> Still grepping through log files to find problems?  Stop.
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> Audacity-nyquist mailing list
> Audacity-nyquist@...
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--
  paul beach
  sniffyraven@...


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