Hi all I have a question on FFT scaling difference between periodic and a periodic signals. if I have a periodic signal x1 (sinewave), the FFT of this signal is normalized by the number of points N to get the correct amplitude spectrum scale < abs(fft(x1))/N >. However if there is aperiodic signal e.g. x2 (square pulse), the normalization by the number of points representing pulse amplitude (k) gives amplitude spectrum with a maximum of 1. what I know is that the spectrum of a square pulse is a sinc waveform of amplitude (A*w). where A is the pulse amplitude and w is the pulse width. does this mean the normalization is different for periodic and aperiodic signals? and if so, how does spectrum analyzers know how to normalize different signals? Any hints? many thanks N = 4096; % number of FFT points ts = 1e-3; % Sampling time t = [0:N-1]*ts; % Time Vector x1 = sin(2*pi*1*t); % Sinewave X1 = abs(fft(x1))/N; % Amplitude spectrum of the sinewave k = 2000; % number of points representing pulse width x2 = [zeros(1,1000) ones(1,k) zeros(1,1096)]; % square pulse of width 2 seconds X2 = abs(fft(x2))/k; % Amplitude Spectrum of the square pulse subplot(2,1,1),plot(X1) subplot(2,1,2),plot(X2)

0 |

10/30/2010 6:14:04 PM

On Oct 30, 11:14=A0am, "abees Tero" <abee...@hotmail.com> wrote: > Hi all >... > > does this mean the normalization is different for periodic and aperiodic = signals? Yes > and if so, how does spectrum analyzers know how to normalize different si= gnals? Spectrum analyzers don't know. In fact, the signal being analyzed may have components that should be scaled in different ways. > > Any hints? > many thanks > ... The three cases are signals that have a power spectrum (tone like), signals that have a power spectral density (PSD) (noise like) and signals that have an energy spectral density (ESD)(transients). As I have posted here before: -begin quote- The PSD, ESD and power spectrum can be calculated via fft based methods in Matlab. Manufacturers of dynamic signal analyzers have provided these functions, properly scaled, for years. Some have been nice enough to accurately document their functions and make and keep the documentation available. Take a look at "Choose your Units!" from B&K: http://www.bksv.com/doc/bo0438.pdf and for more detail, "Signals and Units" on page 29 of: http://www.bksv.com/doc/bv0031.pdf For an discussion of the signal processing, consider pages 5-21 of: http://www.rssd.esa.int/SP/LISAPATHFINDER/docs/Data_Analysis/GH_FFT.pdf Particularly "3 Introduction" on page 5 and "9 Scaling the results" on page 15. I consider "13 Testing the Algorithm" on page 21 and on as a more practically oriented discussion of pwelch than the Matlab docs. -end quote- Dale B. Dalrymple

0 |

10/30/2010 6:37:25 PM

dbd <dbd@ieee.org> wrote in message <1bded1a9-6241-4f2c-85be-d9020e5a2b78@t13g2000yqm.googlegroups.com>... > On Oct 30, 11:14 am, "abees Tero" <abee...@hotmail.com> wrote: > > Hi all > >... > > > > does this mean the normalization is different for periodic and aperiodic signals? > Yes > > and if so, how does spectrum analyzers know how to normalize different signals? > Spectrum analyzers don't know. In fact, the signal being analyzed may > have components that should be scaled in different ways. > > > > Any hints? > > many thanks > > ... > > The three cases are signals that have a power spectrum (tone like), > signals that have a power spectral density (PSD) (noise like) and > signals that have an energy spectral density (ESD)(transients). > > As I have posted here before: > -begin quote- > The PSD, ESD and power spectrum can be calculated via fft based > methods in Matlab. > Manufacturers of dynamic signal analyzers have provided these > functions, properly scaled, for years. Some have been nice enough to > accurately document their functions and make and keep the > documentation available. > > Take a look at "Choose your Units!" from B&K: > > http://www.bksv.com/doc/bo0438.pdf > > and for more detail, "Signals and Units" on page 29 of: > > http://www.bksv.com/doc/bv0031.pdf > > For an discussion of the signal processing, > consider pages 5-21 of: > > http://www.rssd.esa.int/SP/LISAPATHFINDER/docs/Data_Analysis/GH_FFT.pdf > > Particularly "3 Introduction" on page 5 and "9 Scaling the results" on > page 15. > I consider "13 Testing the Algorithm" on page 21 and on as a more > practically oriented discussion of pwelch than the Matlab docs. > -end quote- > > Dale B. Dalrymple Dear Dale,,, I would like to thank you for your kind, fast, really useful response. you cleared all my doubts. thanks again. regards,,,,

0 |

10/30/2010 7:25:05 PM

Hi, I have a little problem with the use of XData. I am plotting and imagesc, for example for the matrix: A=[ 5 6 4 8; 8 12 23 31;15 9 27 5]; The default Xdata scaling would be: 0.5 1 1.5 2 2.5 3 3.5 4 4.5 (as size(A,1)=4 If I want to have (for example): 3 6 9 12, (only in with tick in the center of the squares, ie avoid the intermediate ticks and labels) how can I do? I tried with: x=[3 12]; imagesc(matriz,'XData',x) but that doesn't work well, the ticks are not placed where I want. Please, any help will be very appreciated! "Camille Couzi" <camil...

Hey, i'm working on a project and i actually have an audio signal. After applying to it the fft() function,how can i find the index of the maximum fft value ,and transform it to (Hz) units? I'm a new user so... Thanks a lot. "Dimitris Valapetrou" <diastro@email.com> wrote in message <ht454i$g4r$1@fred.mathworks.com>... > Hey, > i'm working on a project and i actually have an audio signal. > After applying to it the fft() function,how can i find the index > of the maximum fft value ,and transform it to (Hz) units? > I'm a new user...

Dear DSP masters!! I'm using the FFTW C library to evaluate some signal processing ideas. As I have Richard Lyons Understanding ... book I first tried his DFT example of paragraph 3.1.1 in order to check if the FFT results are matching. They did. But I would like to use the FFT to get a correct frequency domain representation, so the outputs must be properly scaled. Note: I'm using the FFTW library with a complex input and a complex output. After the forward FFT operation I divide each individual real and imaginary part by N / 2. And after the inverse FFT operation I divide...

I need some guidance on the following issue Problem : I have a clipped signal Objective ; To reconstruct original value Approach : 1. Make it band limited 2. Apply reconstruction technique Obstacles : 1.I can make the clipped value zeros, and take those as missing values .can any one give me example of band limiting the say between 0 to 50 Hz, 2. Say sampling frequency is 1000 Hz that is sampling interval .001 "kk KKsingh" <akikumar1983@gmail.com> wrote in message <i12igd$9eg$1@fred.mathworks....

hi, i am working on mc-cdma and in most of the papers that i read, the recieved signal vector is written as Y = HCA + N, where H is a channel matrix (rayleigh fading diagonal matrix),C is an orthogonal code matrix and A is the bit vector. N is the noise vector. My doubt is that is there no need to ifft . I mean that is how we transmit it, so is that step not required in the simulations. if yes, then why is it not used in these papers and if no then why not thanks a lot, prateek dayal "Prateek" <prateek@iitg.ac.in> wrote in message news:72a694e0.0312070319.208d489f@posting....

US-TX-Austin: Design Eng., Mixed signal integrated circuit design, Analog Circui (45320957609) ============================================================================================== Position: Design Eng. Reference: SMC01493 Location: Austin TX Duration: Perm Skills: MSEE or MSCE or BSEE plus 5 years of experience. 0-5yrs design experience in mixed-signal integrated circuit design. Strong emphasis on analog design. Exp in one or more of the following: Analog Circuit Design: ...

Hi!!!! I have a amplitude 2 level sine wave signal, for which i have camputed it`s FFT. i have also calculated it`s magnitude. Kindly let me know now how i can obtain amplitude value back from the magnitude values. Gaurav khandre wrote: > > > Hi!!!! > I have a amplitude 2 level sine wave signal, for which i have > camputed it`s FFT. i have also calculated it`s magnitude. Kindly > let > me know now how i can obtain amplitude value back from the > magnitude > values. the answer clear all; clc; Fs=100; t=[0:100]/Fs; s1=5*sin(2*pi*5*t); s2=10*sin(2*pi*10*t); s=(s1+s2);...

US-TX-Austin: Digital or Mixed Signal Design Eng.; 3-8yrs exp., Verilog, DSP, Au (45341757632) ============================================================================================== Position: Digital or Mixed Signal Design Eng. Reference: SMC01777 Location: Austin TX Duration: Perm Skills: BSEE (MSEE preferred) with experience ranging from 3-8 years. Applicants should have skills in the following areas: Verilog Mixed-signal design and simulation tools DSP architectures, synthesis t...

I m using matlab optimization toolbox, namely the function linprog. 1-I obtain these messages using the interior point method: Exiting: One or more of the residuals, duality gap, or total relative error has stalled: the primal appears to be infeasible (and the dual unbounded). (The dual residual < TolFun=1.00e-08.) 2-using simplex method I obtain for the same example : Exiting: Maximum number of iterations exceeded in Phase 1; increase options.MaxIter. what does it mean, and what should I do to solve my problem ? Can someone help me to make the diagnostic ...

US-TX-Austin: DSP Eng., Digital Signal Processing Exp., DSP/Algoritm bckgrnd; DH (45320532404) ============================================================================================== Position: DSP Eng. Reference: SMC01597 Location: Austin TX Duration: DH Skills: Digital Signal Processing Experience. Solid DSP/Algorithm/Communication theory background. Firmware implementation knowledge preferred. BSEE, Master's Preferred - GPA 3.75 or better. Please send your current resume in confidence to <staf...

The FFT function returns Nyquist (half) of input points. How do I get 400 lines of resolution out of 1024 points? Do I just disregard other 112? Thanks In an ideal world, a 1024-point FFT results in 512 valid values, at frequencies from 0/N * Fsamp up to (N/2-1) / N * Fsamp. Of course, an ideal world would also have a filter with 100% pass at the nyquist frequency, and 0% at any frequency above it. T'ain't no such beast. The usual reason for using 400 lines instead of 512 (or 800 instead of 1024, etc.) is the imprecision of the input filters - you don't really know if their cuto...

is it possible to compute symbolic fft by matlab or other sw? Where can i find fft outputs for inputs at each stage of fft radix-2 structure? On 15.01.12 01:42, ahmad salehi wrote: > is it possible to compute symbolic fft by matlab or other sw? See the same question posted two hours earlier by �daryoosh�. Christopher ...

Hi, My hospital has a Philips 3T scanner. We did an abdominal MRI and I wanted to compare adrenal and spleen SI values on a pair of images (in and out of phase T1 weighted images). I compared the numbers reported on the 1) original philips scanner console 2) ge-centricty pacs 3) efilm 1.5.3 4) osirix 1.6.2 only on osirix 1.6.2 were the numbers similar to the philips scanner console. I use a similar size ROI measurement tool on same image, approximate same position. Here is a table of results ip = in phase op = out-of-phase measure device ip-adrenal ip-spleen op-ad...

I can't seem to figure out how to continuiously integrate an accelerometer signal twice to view the displacement. Ive used all of the different integration VI's and i can't seem to get the result i need. i don't want to see a waveform, i just the value of the displacement. Any one help? been at this a long time now. kungfucrazy <x@no.email> wrote in message news:<5065000000080000006FAF0000-1068850981000@exchange.ni.com>... > I can't seem to figure out how to continuiously integrate an > accelerometer signal twice to view the displacement. Ive used al...

I'm trying to scale FFT's to give desireable units. Searching the archives, I cam across this which is very helpful: <http://www.mathworks.com/support/tech-notes/1700/1702.html> but not exactly what I want. So here's the question: If I have a signal (pure sine wave of freq. f) with an amplitude of, let's say 2, I would like to do an FFT and scale it such that the magnitude (i.e., sqrt(power spectrum)) gives a value of 2 at frequency f. Any ideas on how to this for arbitrary amplitudes and frequencies (i.e. arbitrary waveforms)? BTW, the above procedure (from the TMW l...

Hi all I am complete beginner in DSP and FFT in matlab. Thanks for helping guys ! I have a vector of signal x(t) with its time vector. I want to obtain a frequency representation of the signal, in particular the energy spectrum of x(t) in the following definition: _____________________________________________________________________________ I stumbled on this explanation to obtain the energy spectrum, which spells out my intention, from an IEEE paper(Open Circuit Fault Diagnosis in 3 phase uncontrolled rectifiers, 2012, Rahiminejad, Diduch, Stevenson, Chang). "A record...

Dear members, Can any one comment on my below code to plot confidence limits of spectrum calculated using matlab fft. I have implemented following a suggestion from a book but not 100% sure if I am correct in my implementation. Please help In below code I use a time series form a netcdf file But it can be any time series. Also can any one tell me how to obtain variance preserving spectra using matlab and how to plot significance level on it? Sudheer temp=getnc('temp_tser.nc','TEMP'); tsr=temp; cspec=fft(tsr); N=length(tsr); spec=(2./N^2)*abs(cspec)....

US-TX-Austin: Product Marketing Eng.,mixed signal, engineering/design exp; DH (45329614403) =========================================================================================== Position: Product Marketing Eng. Reference: SMC01722 Location: Austin TX Duration: DH Skills: 3+yrs exp in mixed-signal, wireless component industry. Engineering/design exp, combined with exposure/experience in marketing. MS Electrical Engineering or BS Electrical Engineering with graduate studies in business. ...

Hi, i work on project related to video processing.I do programming in MATLAB.I take video from webcam.In which i want to convert this colur video into gray scale video.i get the webcam video preview in matlab.Now i want ot convert this video into gray scale video.What can i do for this? I try but i get nothing. Thanks. ankur wrote: > Hi, > i work on project related to video processing.I do programming in MATLAB.I take video from webcam.In which i want to convert this colur video into gray scale video.i get the webcam video preview in matlab.Now i want ot convert this video into gray...

(apology for cross posting) ********************************************************************** CompIMAGE Computational Modelling of Objects Represented in Images: Fundamentals, Methods and Applications Coimbra, Portugal, October 20-21, 2006 ********************************************************************** Dear Colleague, Please, accept our reminder related with the SUBMISSION PERIOD for the International Symposium CompIMAGE that ENDS TOMORROW (June 30). For more details, including invited speakers, abstracts guidelines and submission, registration and latest news, please see...

It appears that the idea behind fft(X,N) is to save you the trouble of manually zero-padding X when higher frequency sampling is desired (and also to save memory when X is a matrix). However, the format of the zero-padding is always wrong. Note that >> fft([2 1 1],6) ans = Columns 1 through 5 4.0000 2.0000 - 1.7321i 1.0000 2.0000 1.0000 Column 6 2.0000 + 1.7321i is equivalent to >> fft([2 1 1 0 0 0]) ans = Columns 1 through 5 4.0000 2.0000 - 1.7321i 1.0000 2.0000 1.0000...

Abstract: An attempt was made to analytically describe some basic functions which are provided with the libraries of mathematical functions of programming languages. This study will rely on Mathematica in calculating all numerical results. This study provides global methods to calculate some discrete functions, which were previously calculated by using low-level language techniques to chop digits. Using these definitions we can simulate digital signals without the need for IF statements and conditions. A comparison were made between the formulas provided by this study and some funct...

Hi! I want to ask for your advice about a problem i have. I need to perform a FFT every specified amount of time but the FFT calculation takes more tim than i can afford. as an optimization step i want to throw half of th output bins of the FFT but on the FFT structures that i know it'll onl save half of the last stage butterflies calculation. is there any other FFT structure that i can use so I'll save more cycle and I'll be able to work on only half of the spectrum? (1..N samples o the input => bins 1..(N/2-1) on the output) abramovs wrote: > Hi! > I want to ask fo...

hi, i have created a signal y(t) made of a sinosoid , and i added to it white noise n(t) , so as the signal to become s(t)=y(t)+n(t). n(t)= awgn(y,25) and y(t)is for x=0:360 if x<=45 y(i)=-0.6*sind(4*x); else y(i)=0 end now i want to remove the noise n(t) from the signal to get back the original signal y(t). i want to use fft then filter the noise out then ifft however i dont really know how to do the filtering , and according to what. does anyone know how i could do this ? On Jul 7, 7:52 am, "roy zeghondi" <get_r...@hotmail.co...

I would like to ask you to share your experiences of solving structural dynamic equations in frequency domain by use of fft and ifft in matlab. My problem is like this: say, the equation is: m a + c v + k u = p(t) in frequency domain, we should have U(w) = h(w)*P(w), where P(w)=fft(p), and h(w) is the frequency response function then we can get the solution u(t)=ifft(U) My question is how to perform h(w)*P(w)? Thank you very much in advance. I have been hoping to get some help here ... Xiang wrote: > > > I would like to ask you to share your experiences of solving > struc...