From: nitin.abaqus <nitin.abaqus@ya...>  20070822 20:24:58

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  View this message in context: http://www.nabble.com/NyqusitFrequencytf4311804.html#a12275315 Sent from the audacitynyquist mailing list archive at Nabble.com. 
From: David R. Sky <davidsky@sh...>  20070822 22:41:01

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 generallyaccepted 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 plugins 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 > 
From: Sami Jumppanen <sami.jumppanen@gm...>  20070823 09:18:08

Really offtopic, 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 "SomeE" Jumppanen sami.jumppanen@... http://netti.nic.fi/~somee/ 
From: paul beach <sniffyraven@fa...>  20070823 19:40:21

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 offtopic, 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 "SomeE" Jumppanen > sami.jumppanen@... > http://netti.nic.fi/~somee/ > >  > This SF.net email is sponsored by: Splunk Inc. > Still grepping through log files to find problems? Stop. > Now Search log events and configuration files using AJAX and a browser. > Download your FREE copy of Splunk now >> http://get.splunk.com/ > _______________________________________________ > Audacitynyquist mailing list > Audacitynyquist@... > https://lists.sourceforge.net/lists/listinfo/audacitynyquist  paul beach sniffyraven@... 