Dear all, I have a vibrations report and I have some experience with making FFT's from university. However not too much experience and never with vibrations specifically. Now I want to ask you guys for help for getting a better understanding: 1) An impulse hammer was used to find resonance frequencies. As I understand it, this impulse hammer is starting from a low frequency and then increases the frequency up to some maximum frequency. The response is then measured to find "natural/resonance frequencies"... I once tried this in Matlab and played back the sound - it was a steady increasing pitch. I used a chirp signal... Is the impulse hammer behaviour exactly like a chirp signal, i.e. starts from low frequency and then rises slowly to higher frequencies? 2) Let's say I have vibration signals from a structure measured by either accelerometer or by proximity probe (I still don't understand the difference completely). Can some of you please make the following clear to me: "The vibrations are measured using accelerometers and proximity sensors. Vibration data is usually presented as vibration velocity in units [mm/s]. In order to convert from acceleration to velocity, the acceleration signal is integrated numerically with respect to time (v = a*dt)." I tried to google for the difference, but as I understand it accelerometers measure in m/s^2 whereas the proximity probes measure in m/s ??? Is this true? The report also writes: "In order to avoid erroneous effects at very low frequencies, a high pass filter at 10 Hz is applied to the signal. Double integration (also with a 10 Hz-high pass filter) is used to compute displacement. Displacement signals of the proximity sensors can be converted to velocity by numerical differentiation." This is don't quite follow... Anyone does and can explain? 3) Suppose I take this audio input signal and load it into Matlab: http://www.moviewavs.com/0053665484/WAVS/TV_Shows/Simpsons/smart.wav How would you go on making an FFT plot of that, which looks like the following (please show me the code): A) 2D-plot with: Time in [seconds] on x-axis, frequency along y-axis, no colorbar since everything should just be blue lines. B) 3D-plot with: Time in [seconds] on one axis, frequency along another axis and root mean square of velocities along the third axis (these are perhaps measured by proximity probes?)? The report says this plot is also sometimes made by using a waterfall-diagram. C) 2D-plot of the above, but with a color bar that has values from 0 to maximum of root-mean-square of velocities... D) The author of the report make this kind of plot: +-----+---+ | | | | 1. | 2.| | | | +-----+---+ | 3. | +---------+ Where the windows are: (1) Top left: is the FFT plot like described under (C) above, i.e. I think the x-axis is time (there's no x-axis in window 1) because that is shown under window (3) and frequency is definately shown along y-axis. (2) Top right: is a "peak hold spectrum for the time segment". The x-axis shows velocity and there's no y-axis. Therefore I assume the y-axis is that from window 1, i.e. frequency. (3) Bottom: Here we have a plot with time along x-axis and velocity along y-axis. I guess this is just the measurements... Question: Is this a normal way of presenting results and what exactly does the "peak hold" curve show and how do I create it in Matlab with an arbitrary wav-file? I think that the "peak hold"-curve shows the maximum velocity for a given frequency (i.e. max. velocity on x-axis and frequency on y-axis). I hope somebody can help me with so the confusion disappears and hopefully you also find this interesting. Thanks!
DSP-newbie: Need help with FFT of signal and engineering report
Started by ●January 17, 2009
Reply by ●January 17, 20092009-01-17
On 18 Jan, 00:05, "Hr. Hansen" <han...@hotmail.com> wrote:> Dear all, > > I have a vibrations report and I have some experience with making FFT's > from university. However not too much experience and never with > vibrations specifically. Now I want to ask you guys for help for getting > a better understanding: > > 1) > An impulse hammer was used to find resonance frequencies. As I > understand it, this impulse hammer is starting from a low frequency and > then increases the frequency up to some maximum frequency. The response > is then measured to find "natural/resonance frequencies"... I once tried > this in Matlab and played back the sound - it was a steady increasing > pitch. I used a chirp signal... Is the impulse hammer behaviour exactly > like a chirp signal, i.e. starts from low frequency and then rises > slowly to higher frequencies?I would *guess* that the impulse hammer pecks the structure with varying intervals, and thus emulates the general bevahviour of a chirp. The workings are different from the chirp, and regular chirp-based techniques may or may not work.> 2) > Let's say I have vibration signals from a structure measured by either > accelerometer or by proximity probe (I still don't understand the > difference completely). Can some of you please make the following clear > to me: > > "The vibrations are measured using accelerometers and proximity sensors. > Vibration data is usually presented as vibration velocity in units > [mm/s]. In order to convert from acceleration to velocity, the > acceleration signal is integrated numerically with respect to time (v = > � �a*dt)." > > I tried to google for the difference, but as I understand it > accelerometers measure in m/s^2 whereas the proximity probes measure in > m/s ??? Is this true?Acellerometers measure acceleration. If you measure velocity you would use a 'velocimeter'. I haven't heard the term 'proximity probe', but I would *guess* that the term indicates that it measures distance directly. If that's correct, you would need to differentiate the data to obtain velocity.> The report also writes: > > "In order to avoid erroneous effects at very low frequencies, a high > pass filter at 10 Hz is applied to the signal. Double integration (also > with a 10 Hz-high pass filter) is used to compute displacement. > Displacement signals of the proximity sensors can be converted to > velocity by numerical differentiation." > > This is don't quite follow... Anyone does and can explain?Just physics 101. The relations between acceleration, velocity and travelled distance.> How would you go on making an FFT plot of that, which looks like the > following (please show me the code):Ser du har postet i norske grupper, s� jeg antar du er norsk. Jeg kan hjelpe med dette, men i litt mer ordnede former enn her. Gi et hint her om du trenger assistanse (emailaddressen du ser er ugyldig men indikerer hvor i landet jeg befinner meg), s� tar jeg kontakt. Rune
Reply by ●January 18, 20092009-01-18
On Jan 17, 6:05�pm, "Hr. Hansen" <han...@hotmail.com> wrote:> Dear all, > > I have a vibrations report and I have some experience with making FFT's > from university. However not too much experience and never with > vibrations specifically. Now I want to ask you guys for help for getting > a better understanding: > > 1) > An impulse hammer was used to find resonance frequencies. As I > understand it, this impulse hammer is starting from a low frequency and > then increases the frequency up to some maximum frequency. The response > is then measured to find "natural/resonance frequencies"... I once tried > this in Matlab and played back the sound - it was a steady increasing > pitch. I used a chirp signal... Is the impulse hammer behaviour exactly > like a chirp signal, i.e. starts from low frequency and then rises > slowly to higher frequencies? > > 2) > Let's say I have vibration signals from a structure measured by either > accelerometer or by proximity probe (I still don't understand the > difference completely). Can some of you please make the following clear > to me: > > "The vibrations are measured using accelerometers and proximity sensors. > Vibration data is usually presented as vibration velocity in units > [mm/s]. In order to convert from acceleration to velocity, the > acceleration signal is integrated numerically with respect to time (v = > � �a*dt)." > > I tried to google for the difference, but as I understand it > accelerometers measure in m/s^2 whereas the proximity probes measure in > m/s ??? Is this true? > > The report also writes: > > "In order to avoid erroneous effects at very low frequencies, a high > pass filter at 10 Hz is applied to the signal. Double integration (also > with a 10 Hz-high pass filter) is used to compute displacement. > Displacement signals of the proximity sensors can be converted to > velocity by numerical differentiation." > > This is don't quite follow... Anyone does and can explain? > > 3) > Suppose I take this audio input signal and load it into Matlab:http://www.moviewavs.com/0053665484/WAVS/TV_Shows/Simpsons/smart.wav > > How would you go on making an FFT plot of that, which looks like the > following (please show me the code): > > A) 2D-plot with: Time in [seconds] on x-axis, frequency along y-axis, no > colorbar since everything should just be blue lines. > > B) 3D-plot with: Time in [seconds] on one axis, frequency along another > axis and root mean square of velocities along the third axis (these are > perhaps measured by proximity probes?)? The report says this plot is > also sometimes made by using a waterfall-diagram. > > C) 2D-plot of the above, but with a color bar that has values from 0 to > maximum of root-mean-square of velocities... > > D) The author of the report make this kind of plot: > > +-----+---+ > | � � | � | > | �1. | 2.| > | � � | � | > +-----+---+ > | � 3. � �| > +---------+ > > Where the windows are: > > � (1) Top left: is the FFT plot like described under (C) above, i.e. I > think the x-axis is time (there's no x-axis in window 1) because that is > shown under window (3) and frequency is definately shown along y-axis. > > � (2) Top right: is a "peak hold spectrum for the time segment". The > x-axis shows velocity and there's no y-axis. Therefore I assume the > y-axis is that from window 1, i.e. frequency. > > � (3) Bottom: Here we have a plot with time along x-axis and velocity > along y-axis. I guess this is just the measurements... > > Question: Is this a normal way of presenting results and what exactly > does the "peak hold" curve show and how do I create it in Matlab with an > arbitrary wav-file? I think that the "peak hold"-curve shows the maximum > velocity for a given frequency (i.e. max. velocity on x-axis and > frequency on y-axis). > > I hope somebody can help me with so the confusion disappears and > hopefully you also find this interesting. > > Thanks!Don't know if it'll help, but there's a web site devoted to vibration analysis with a lot of links: http://www.plant-maintenance.com/maintenance_articles_vibration.shtml You might also look through the library link at: http://www.dliengineering.com/ They also have a vibration manual that briefly discusses transducer types: http://www.dliengineering.com/vibman/Alan2-toc.htm Kevin
Reply by ●January 18, 20092009-01-18
Rune Allnor wrote, On 1/18/09 2:01 AM:> On 18 Jan, 00:05, "Hr. Hansen" <han...@hotmail.com> wrote: >> Dear all, >> 2) >> Let's say I have vibration signals from a structure measured by either >> accelerometer or by proximity probe (I still don't understand the >> difference completely). Can some of you please make the following clear >> to me: >> >> "The vibrations are measured using accelerometers and proximity sensors. >> Vibration data is usually presented as vibration velocity in units >> [mm/s]. In order to convert from acceleration to velocity, the >> acceleration signal is integrated numerically with respect to time (v = >> a*dt)." >> >> I tried to google for the difference, but as I understand it >> accelerometers measure in m/s^2 whereas the proximity probes measure in >> m/s ??? Is this true? > > Acellerometers measure acceleration. If you measure velocity > you would use a 'velocimeter'. I haven't heard the termDoes anything called a velocimeter exist? I would guess you always measure distances...> 'proximity probe', but I would *guess* that the term indicates > that it measures distance directly. If that's correct, you would > need to differentiate the data to obtain velocity.If accelerometer doesn't measure distances directly, how does it work?>> The report also writes: >> >> "In order to avoid erroneous effects at very low frequencies, a high >> pass filter at 10 Hz is applied to the signal. Double integration (also >> with a 10 Hz-high pass filter) is used to compute displacement. >> Displacement signals of the proximity sensors can be converted to >> velocity by numerical differentiation." >> >> This is don't quite follow... Anyone does and can explain? > > Just physics 101. The relations between acceleration, velocity and > travelled distance.No, not physics 101. High pass filter is applied and then double integrated also with another high pass filter or something... How do you explain it?>> How would you go on making an FFT plot of that, which looks like the >> following (please show me the code): > > Ser du har postet i norske grupper, s� jeg antar du er norsk.Er comp.dsp norsk? Men jeg er dansk :-)> Jeg kan hjelpe med dette, men i litt mer ordnede former enn > her. Gi et hint her om du trenger assistanse (emailaddressen > du ser er ugyldig men indikerer hvor i landet jeg befinner meg), > s� tar jeg kontakt.Tak for tilbuddet, men jeg er i K�benhavn DK :-) S� jeg m� hellere takke nej til tilbuddet. Og f�rst og fremmest ville jeg bare se et FFT-script og k�re det gennem Matlab. Derefter vil jeg pr�ve at lave tilsvarende plots som den figur med 3 vinduer jeg viste... Og s� er jeg f�rdig... Jeg har erfaring med FFT fra billedbehandling, men er ikke voldsomt god til det og det er lang tid siden s� jeg h�bede nogen i nyhedsgruppen lige kunne vise mig et kort script til gavn for alle...
Reply by ●January 18, 20092009-01-18
kevinjmcgee@netscape.net wrote, On 1/18/09 5:45 AM: > On Jan 17, 6:05 pm, "Hr. Hansen" <han...@hotmail.com> wrote: > Don't know if it'll help, but there's a web site devoted to vibration > analysis with a lot of links: > > http://www.plant-maintenance.com/maintenance_articles_vibration.shtml > > You might also look through the library link at: > > http://www.dliengineering.com/ > > They also have a vibration manual that briefly discusses transducer > types: > > http://www.dliengineering.com/vibman/Alan2-toc.htm Yes, google gives a hell of a lot hits but I have trouble finding a simple FFT-script that transforms a wav file or whatever into an fft-plot... BTW: Stupid me used the wrong e-mail address earlier so if you, Rune or anyone else want to private mail me an FFT-script for Matlab (or Octave).
Reply by ●January 18, 20092009-01-18
On 18 Jan, 14:51, "Hr. Hansen" <han...@hotmail.com> wrote:> Rune Allnor wrote, On 1/18/09 2:01 AM: > > > > > > > On 18 Jan, 00:05, "Hr. Hansen" <han...@hotmail.com> wrote: > >> Dear all, > >> 2) > >> Let's say I have vibration signals from a structure measured by either > >> accelerometer or by proximity probe (I still don't understand the > >> difference completely). Can some of you please make the following clear > >> to me: > > >> "The vibrations are measured using accelerometers and proximity sensors. > >> Vibration data is usually presented as vibration velocity in units > >> [mm/s]. In order to convert from acceleration to velocity, the > >> acceleration signal is integrated numerically with respect to time (v = > >> � �a*dt)." > > >> I tried to google for the difference, but as I understand it > >> accelerometers measure in m/s^2 whereas the proximity probes measure in > >> m/s ??? Is this true? > > > Acellerometers measure acceleration. If you measure velocity > > you would use a 'velocimeter'. I haven't heard the term > > Does anything called a velocimeter exist? I would guess you always > measure distances...I used to work with velocity data. I always assumed they were measured directly, but I can't remember having seen the specs of the actual instrument... not that I had much oportunity. The data (let alone the sensors) were closely guarded trade secrets at the time. As for what you measure, it depends on the physics of the sensors. Some measurements are easier than others, or require simpler or less expensive sensor devices.> > 'proximity probe', but I would *guess* that the term indicates > > that it measures distance directly. If that's correct, you would > > need to differentiate the data to obtain velocity. > > If accelerometer doesn't measure distances directly, how does it work?It measures the acceleration of the sensor. The physics depends on exactly what type of senor you are talking about.> >> The report also writes: > > >> "In order to avoid erroneous effects at very low frequencies, a high > >> pass filter at 10 Hz is applied to the signal. Double integration (also > >> with a 10 Hz-high pass filter) is used to compute displacement. > >> Displacement signals of the proximity sensors can be converted to > >> velocity by numerical differentiation." > > >> This is don't quite follow... Anyone does and can explain? > > > Just physics 101. The relations between acceleration, velocity and > > travelled distance. > > No, not physics 101. High pass filter is applied and then double > integrated also with another high pass filter or something... How do you > explain it?These are two different processes. The high-pass filter is to clean up the data in thesense 'remove long-time trends'. The double integration is to convert from acceleration to displacement. The second high-pass filter is to remove even more noise from the result.> >> How would you go on making an FFT plot of that, which looks like the > >> following (please show me the code): > > > Ser du har postet i norske grupper, s� jeg antar du er norsk. > > Er comp.dsp norsk? Men jeg er dansk :-)Beklager. Jeg s� p� historeien for � se tidligere poster fra signaturen din. Pleier � gj�re det med skandinavisk-lignede signaturer. Der var det et par norske grupper som dukket opp. Rune
Reply by ●January 18, 20092009-01-18
Rune Allnor wrote, On 1/18/09 3:12 PM:> On 18 Jan, 14:51, "Hr. Hansen" <han...@hotmail.com> wrote: >> Rune Allnor wrote, On 1/18/09 2:01 AM: > These are two different processes. The high-pass filter is to > clean up the data in thesense 'remove long-time trends'. The > double integration is to convert from acceleration to displacement. > The second high-pass filter is to remove even more noise from > the result.Okay, thanks for those details. They're not that important right now because I'll play with these filters once I get the FFT-algorithm to work and has created the plots... Doesn't anyone in here has any FFT-code to show? I cannot believe that... Just some code I can copy/paste to get started and then I want to play with filters and compare with the vibrations-report...
Reply by ●January 18, 20092009-01-18
Hr. Hansen wrote, On 1/18/09 4:25 PM:> Rune Allnor wrote, On 1/18/09 3:12 PM: >> On 18 Jan, 14:51, "Hr. Hansen" <han...@hotmail.com> wrote: >>> Rune Allnor wrote, On 1/18/09 2:01 AM: >> These are two different processes. The high-pass filter is to >> clean up the data in thesense 'remove long-time trends'. The >> double integration is to convert from acceleration to displacement. >> The second high-pass filter is to remove even more noise from >> the result. > > Okay, thanks for those details. They're not that important right now > because I'll play with these filters once I get the FFT-algorithm to > work and has created the plots... > > > Doesn't anyone in here has any FFT-code to show? I cannot believe > that... Just some code I can copy/paste to get started and then I want > to play with filters and compare with the vibrations-report...Okay, here's what I found on google, but I'm not close yet (slightly modified, just copy/paste to run): ---------- clear all close all clc %http://www.moviewavs.com/0053665484/WAVS/TV_Shows/Simpsons/smart.wav inputFile = 'd:\\smart.wav'; fileSize = wavread(inputFile, 'size'); numSamples = 2.^(ceil(log2(fileSize(1)))); % round up to nearest power of 2 x = zeros(numSamples, 1); % zero pad if necessary [inputBuffer, Fs] = wavread(inputFile); x(1:fileSize(1)) = inputBuffer(:,1); % if multi-channel, use left channel only clear inputBuffer; % free this memory clear fileSize; Ts = 1/Fs; % Fs is sampling frequency, Ts is sampling period t = linspace(0, (numSamples-1)*Ts, numSamples)'; f = linspace(-Fs/2, Fs/2 - Fs/numSamples, numSamples)'; X = fft(x); plot(t, x); xlabel('time (seconds)'); ylabel('amplitude'); title(['time-domain plot of ' inputFile]); sound(x, Fs); % play the sound %wavplay(x,fs,'async'); pause; % display both positive and negative frequency spectrum plot(f, real(fftshift(X))); xlabel('frequency (Hz)'); ylabel('real part'); title(['real part frequency-domain plot of ' inputFile]); pause; plot(f, imag(fftshift(X))); xlabel('frequency (Hz)'); ylabel('imag part'); title(['imag part frequency-domain plot of ' inputFile]); pause; plot(f, abs(fftshift(X))); % linear amplitude by linear freq plot xlabel('frequency (Hz)'); ylabel('amplitude'); title(['abs frequency-domain plot of ' inputFile]); pause; plot(f, 20*log10(abs(fftshift(X))+1.0e-10)); % dB by linear freq plot xlabel('frequency (Hz)'); ylabel('amplitude (dB)'); title(['dB frequency-domain plot of ' inputFile]); pause; % display only positive frequency spectrum for log frequency scale semilogx(f(numSamples/2+2:numSamples), 20*log10(abs(X(2:numSamples/2)))); % dB by log freq plot xlabel('frequency (Hz), log scale'); ylabel('amplitude (dB)'); title(['dB vs. log freq, frequency-domain plot of ' inputFile]); pause; semilogx(f(numSamples/2+2:numSamples), (180/pi)*angle(X(2:numSamples/2))); % phase by log freq plot xlabel('frequency (Hz), log scale'); ylabel('phase (degrees)'); title(['phase vs. log freq, frequency-domain plot of ' inputFile]); pause; % % this is an alternate method of unwrapping phase % % phase = cumsum([angle(X(1)); angle( X(2:numSamples/2) ./X(1:numSamples/2-1) ) ]); % semilogx(f(numSamples/2+2:numSamples), phase(2:numSamples/2)); %unwrapped phase by log freq plot semilogx(f(numSamples/2+2:numSamples), unwrap(angle(X(2:numSamples/2)))); % unwrapped phase by log freq plot xlabel('frequency (Hz), log scale'); ylabel('unwrapped phase (radians)'); title(['unwrapped phase vs. log freq, frequency-domain plot of ' inputFile]); ------------ To quote myself, this is what I want: The author of the report make this kind of plot: > > +-----+---+ > | | | > | 1. | 2.| > | | | > +-----+---+ > | 3. | > +---------+ > > Where the windows are: > > (1) Top left: is the FFT plot like described under (C) above, i.e. I > think the x-axis is time (there's no x-axis in window 1) because that is > shown under window (3) and frequency is definately shown along y-axis. > > (2) Top right: is a "peak hold spectrum for the time segment". The > x-axis shows velocity and there's no y-axis. Therefore I assume the > y-axis is that from window 1, i.e. frequency. > > (3) Bottom: Here we have a plot with time along x-axis and velocity > along y-axis. I guess this is just the measurements... hmmm... Addition: I think window 1 is made with something like: spectrogram(x, [], [], [], Fs, 'yaxis'); Do you understand the "peak hold" curve? How do I create it in Matlab? I think that the "peak hold"-curve shows the maximum velocity for a given frequency (i.e. max. velocity on x-axis and frequency on y-axis). Well... If you have any comments feel free to bring them here and if not, I fully understand that it's not easy to discuss over usenet/mail etc. Perhaps I'll talk to some people in my company who knows more about DSP than me...
Reply by ●January 18, 20092009-01-18
Hr. Hansen wrote:> Yes, google gives a hell of a lot hits but I have trouble finding a > simple FFT-script that transforms a wav file or whatever into an > fft-plot...[SoundData, Frequency] = wavread(FILENAME); FFTofSound = fft(SoundData, Frequency); plot( 0:length(FFTofSound), abs(FFTofSound)); -- .signature note: I am now avoiding replying to unclear or ambiguous postings. Please review questions before posting them. Be specific. Use examples of what you mean, of what you don't mean. Specify boundary conditions, and data classes and value relationships -- what if we scrambled your data or used -Inf, NaN, or complex(rand,rand)?
Reply by ●January 18, 20092009-01-18
On Sun, 18 Jan 2009 14:51:07 +0100, "Hr. Hansen" <hansen@hotmail.com> wrote:>Rune Allnor wrote, On 1/18/09 2:01 AM: >> On 18 Jan, 00:05, "Hr. Hansen" <han...@hotmail.com> wrote: >>> Dear all, >>> 2) >>> Let's say I have vibration signals from a structure measured by either >>> accelerometer or by proximity probe (I still don't understand the >>> difference completely). Can some of you please make the following clear >>> to me: >>> >>> "The vibrations are measured using accelerometers and proximity sensors. >>> Vibration data is usually presented as vibration velocity in units >>> [mm/s]. In order to convert from acceleration to velocity, the >>> acceleration signal is integrated numerically with respect to time (v = >>> a*dt)." >>> >>> I tried to google for the difference, but as I understand it >>> accelerometers measure in m/s^2 whereas the proximity probes measure in >>> m/s ??? Is this true? >> >> Acellerometers measure acceleration. If you measure velocity >> you would use a 'velocimeter'. I haven't heard the term > >Does anything called a velocimeter exist? I would guess you always >measure distances...Yes it exists, but I've not heard it called velocometer before, though I can immediately tell what the word means from its root words.> >> 'proximity probe', but I would *guess* that the term indicates >> that it measures distance directly. If that's correct, you would >> need to differentiate the data to obtain velocity. > >If accelerometer doesn't measure distances directly, how does it work?Imagine a box with a spring inside, attached to the bottom. At the other end of the spring is a mass. This thing will oscillate up and down, but that's not desired so lets assume it's damped. With the box itting upright, the spring is compressed by the mass pulling down to Earth. Upside down, the mass stretches the spring. Put the thing rightside up on a rocket and fire the rocket up. The spring will compress more than when sitting upright, caused by the acceleration of the rocket being greater than Earth's gravity. Measuring the position of the mass (how compressed the spring is) tells you the acceleration the box is experiencing. If you integrate the acceleration signal, you will get position (plus a constant, of course, as learned in Calculus - the physics interpretation of the constant is your starting position). And yes, it's "lossy" in that the absolute position becomes inaccurate over time due to the way it works, but it's still useful.> >>> The report also writes: >>> >>> "In order to avoid erroneous effects at very low frequencies, a high >>> pass filter at 10 Hz is applied to the signal. Double integration (also >>> with a 10 Hz-high pass filter) is used to compute displacement. >>> Displacement signals of the proximity sensors can be converted to >>> velocity by numerical differentiation." >>> >>> This is don't quite follow... Anyone does and can explain? >> >> Just physics 101. The relations between acceleration, velocity and >> travelled distance. > >No, not physics 101. High pass filter is applied and then double >integrated also with another high pass filter or something... How do you >explain it? > >>> How would you go on making an FFT plot of that, which looks like the >>> following (please show me the code): >> >> Ser du har postet i norske grupper, s� jeg antar du er norsk. > >Er comp.dsp norsk? Men jeg er dansk :-) > >> Jeg kan hjelpe med dette, men i litt mer ordnede former enn >> her. Gi et hint her om du trenger assistanse (emailaddressen >> du ser er ugyldig men indikerer hvor i landet jeg befinner meg), >> s� tar jeg kontakt. > >Tak for tilbuddet, men jeg er i K�benhavn DK :-) > >S� jeg m� hellere takke nej til tilbuddet. Og f�rst og fremmest ville >jeg bare se et FFT-script og k�re det gennem Matlab. > >Derefter vil jeg pr�ve at lave tilsvarende plots som den figur med 3 >vinduer jeg viste... Og s� er jeg f�rdig... > >Jeg har erfaring med FFT fra billedbehandling, men er ikke voldsomt god >til det og det er lang tid siden s� jeg h�bede nogen i nyhedsgruppen >lige kunne vise mig et kort script til gavn for alle... >
