Path: news.mathworks.com!not-for-mail
From: "Aymen " <aymenkoobar@gmail.com>
Newsgroups: comp.soft-sys.matlab
Subject: Re: generate Time signal from a given PSD
Date: Wed, 4 Nov 2009 07:48:03 +0000 (UTC)
Organization: Universit&#228;t Stuttgart
Lines: 29
Message-ID: <hcrbjj$6m5$1@fred.mathworks.com>
References: <hcpgp2$7r6$1@fred.mathworks.com> <4fa464e4-319c-4c19-8493-2d46c075cdf2@m3g2000pri.googlegroups.com>
Reply-To: "Aymen " <aymenkoobar@gmail.com>
NNTP-Posting-Host: webapp-03-blr.mathworks.com
Content-Type: text/plain; charset="ISO-8859-1"
Content-Transfer-Encoding: 8bit
X-Trace: fred.mathworks.com 1257320883 6853 172.30.248.38 (4 Nov 2009 07:48:03 GMT)
X-Complaints-To: news@mathworks.com
NNTP-Posting-Date: Wed, 4 Nov 2009 07:48:03 +0000 (UTC)
X-Newsreader: MATLAB Central Newsreader 1357504
Xref: news.mathworks.com comp.soft-sys.matlab:582280


TideMan <mulgor@gmail.com> wrote in message <4fa464e4-319c-4c19-8493-2d46c075cdf2@m3g2000pri.googlegroups.com>...
> On Nov 4, 4:04?am, "Aymen " <aymenkoo...@gmail.com> wrote:
> > Hello people,
> > ?i'm a novice in the field of signal processing and this problem maybe easy for you ...
> > I want to extract a stochastic time signal from a given PSD using the inverse fourier transform.
> > the PSD contains frequencies from 0 to 2557,5 and i'm trying to generate a time signal corresponding to that PSD (it goes over a time period of 35 sec ).
> > I think i'm having a scaling problem but i don't know where ...
> > could you please help me with this :
> >
> > First of all i tried to generate random phases for my PSD-amplitudes to be able to perform the ifft.
> > M=[freq Amplitude]; ?%PSD Matrix
> > a=sqrt(Amplitude);
> > phase = 2*pi*rand(size(a)); %random phases in [0 ?2*pi]
> > Y=a.*exp(j*phase); ?% complex vector for ifft
> >
> > signal = ifft(Y,N); %inverse Fourier Transform, problem in N ??????
> > t=0:35/(N-1):35; %time vector
> > plot(t,real(signal)) %plot of time signal
> >
> > my time vector sould have 179200 values between 0 sec and 35 sec
> >
> > which N should i use to get the correct answer ?
> 
> Why haven't you followed the instructions I gave you here:
> http://groups.google.com/group/comp.soft-sys.matlab/browse_thread/thread/daa041121df922ea/7ea8124eb997d9c3#7ea8124eb997d9c3
> 
> I told you how to build Y, but you haven't done that.
> Why not?
i did it that way first but the signal i got was nearly the same... i must get a signal that is nearly 10^5 times bigger in amplitude than my signal...