## IFFT

Started by in comp.dsp12 years ago 2 replies

Hi All, I am trying to implement a Fast Fourier Transform, followed by an Inverse FFT on the iPhone in Objective-C. To do this I am using...

Hi All, I am trying to implement a Fast Fourier Transform, followed by an Inverse FFT on the iPhone in Objective-C. To do this I am using the functions within the 'rvfft.cpp' file available here: http://www.musicdsp.org/archive.php?classid=2#79 I am trying to perform the operation on an array of doubles of length 131072 (padded with zeros to ensure it is divisible by 2). My code is belo...

## anyone have an answer to this?

Started by in comp.dsp15 years ago 15 replies

Hi there, Just wondering if this question was answered...I know it is an old post, but just taking a long shot here. Essentially I am getting...

Hi there, Just wondering if this question was answered...I know it is an old post, but just taking a long shot here. Essentially I am getting the same outcome...specifically, in matlab, I can generate an appropriate correlation plot, and retrieve the correct delay with xcorr...as well as using the TF method : max(ifft(fft(x1).*conj(fft(x2))), i.e. through regular cross correlation. However, ...

## Bandfilters with FFT on Sampled in-/output

Started by in comp.dsp12 years ago 10 replies

Hello all, Currently i am working on echo cancellation software for a voice communication system. and i came across the following problem: I...

Hello all, Currently i am working on echo cancellation software for a voice communication system. and i came across the following problem: I need to analyse and filter frequency's, so i do a FFT i cut off some frequency's and then perform an iFFT to get the filtered signal. This happens on sample's varying between 20ms and 1000ms (2^9 to 2^16). The frequency's that i whant to get rid of are ...

## Measuring circuit delay and impulse response

Started by in comp.dsp12 years ago 3 replies

Hi, Is there a way to measure a circuit's delay and the impulse response? For instance is there a way where I can take S-parameter...

Hi, Is there a way to measure a circuit's delay and the impulse response? For instance is there a way where I can take S-parameter measurements and inverse it using IFFT at a certain frequency range? Will it be an accurate measurement?

## convert ferquency domain to time domain

Started by in comp.dsp18 years ago 1 reply

pls help how to convert frequency domain to time domain by IFFT. thanks for all utomo This message was sent using the Comp.DSP web...

pls help how to convert frequency domain to time domain by IFFT. thanks for all utomo This message was sent using the Comp.DSP web interface on DSPRelated.com

## From s space to time response with FFT

Started by in comp.dsp18 years ago 2 replies

Hi! I am looking for a method that can take an s domain transfer function and use FFT/IFFT to obtain the discrete time domain impulse...

Hi! I am looking for a method that can take an s domain transfer function and use FFT/IFFT to obtain the discrete time domain impulse response. Are there any aproximations that allow that? Thanks! Atmapuri.

## complex output from matlab IFFT

Started by in comp.dsp17 years ago 17 replies

Why am i getting complex output when i compute the inverse fft of a vector of complex numbers? This does not happen always and the imaginary...

Why am i getting complex output when i compute the inverse fft of a vector of complex numbers? This does not happen always and the imaginary part of the output is very small compared to the real part. thanks for any insight jeremy

## circular convolution or matrix multiplication

Started by in comp.dsp14 years ago 6 replies

Hi, I'm currently doing project on OFDM based. I want to transmit my signal through a Rayleigh channel. assume that the received signal should...

Hi, I'm currently doing project on OFDM based. I want to transmit my signal through a Rayleigh channel. assume that the received signal should be y(t)=x(t)*h(t)+n(t) or Y(f)=X(f)H(f)+N(f). I understand that in order to get y(t), we need to do a convolution between x(t) and h(t). let say, after IFFT in OFDM part, then I change the signal into serial where the data is in time domain. Now, I don...

## concatenated FFT's?

Started by in comp.dsp18 years ago 1 reply

I read about something like the following before, but don't know what search terms to feed Google in order to find it. If I have only the FFT...

I read about something like the following before, but don't know what search terms to feed Google in order to find it. If I have only the FFT results, length N, for 2 successive frames of data, naively I can get an FFT of length 2N by first doing two IFFT's and then an FFT on the concatenation of their output. Is there a more efficient method? IMHO. YMMV. -- Ron Nicholson rhn AT ...

## OFDM Transmit diversity

Started by in comp.dsp16 years ago 3 replies

Hello, Assume you have 2 OFDM transmitters that are simultanously transmitting different data and the data is somehow coded (ie...

Hello, Assume you have 2 OFDM transmitters that are simultanously transmitting different data and the data is somehow coded (ie CDMA). After IFFT the ofdm symbol of each transmitter , X1 and X2, passes a freq. selective fading channel: Y = X1.G1 + X2.G2 + N My question is at the receiver, before or after the FFT, how to remove the effect G1 and G2 which are the fading coeffici...

## WARNING: Is there a use for ifft(X,M)?

Started by in comp.dsp14 years ago 19 replies

This is a followup to the thread "Why is fft(x,M) useful? http://groups.google.com/group/comp.soft-sys.matlab/ msg/2bacfcce9454065e As long...

This is a followup to the thread "Why is fft(x,M) useful? http://groups.google.com/group/comp.soft-sys.matlab/ msg/2bacfcce9454065e As long as the N components of the time sampled row vector function x are presented in chronological order, the use of fft(x,M) as shorthand for the zeropadding operation fft([x,zeros(1,M-N)]) is relatively straightforward. In contrast, it has been show ...

## How to begin with DSPs

Started by in comp.dsp16 years ago 7 replies

Hi all I have implemented a non-realtime DVB-T receiver in C++ and tested it successfully with signals off the air. Now I have to implement a...

Hi all I have implemented a non-realtime DVB-T receiver in C++ and tested it successfully with signals off the air. Now I have to implement a real-time receiver. The baseband signal processing includes time and frequendy synchronization, channel estimation, coherent demodulation and docoding. The corresponding caculations are - arithmatic calculation - correlation - FFT and IFFT - matrix in...

## s the output of an analog filter real or the magnitude?(2)

Started by in comp.dsp17 years ago 3 replies

Hello again and thank you for your answers I will try to describe my scenario 1. I am working with UWB signals, which is real, s(t), and has...

Hello again and thank you for your answers I will try to describe my scenario 1. I am working with UWB signals, which is real, s(t), and has Fourier transform S(w). 2. I apply one filter H(w), which has gain A(w) and phase Theta(w), w = angular frequency. Then H(w) = A(w)*exp(j*Tetha(w)*to); 3. In digital domain, I decide what I get, lets say the real part, real(ifft(S(w)*H(w))), or the imagin...

## Resampling

Started by in comp.dsp17 years ago 26 replies

Dear, I want to resample a real signal from for instance 1024 -> 1027 samples. I prefer not to do it in the temporal domain, in order to...

Dear, I want to resample a real signal from for instance 1024 -> 1027 samples. I prefer not to do it in the temporal domain, in order to avoid large upsampling and downsampling steps. I have read that one possibility could be zero padding in frequency, but for this example I must use a IDFT and not IFFT to transform the signal to time domain. I have heard something about chirp-z transform, but

## How can i verify how many samples have i skipped (OFDM QUESTION)

Started by in comp.dsp15 years ago 1 reply

hi all DSP giants and experts, i am struggling on one problem..lemme share with you people.. Thanks...

hi all DSP giants and experts, i am struggling on one problem..lemme share with you people.. Thanks in advance for all answers its like this i have OFDM Symbols say 256 ifft which has a cylic prefix of 32 say a system is taking fft at some sample offset..i need to know..at what sample offset from start. the FLOW is like this step1-===...

## Interesting problem

Started by in comp.dsp18 years ago 1 reply

I am a newcomer in DSP. I am using MATLAB for that.My data is in form of a N*1 matrix. Why there is phase associated with it though its all real...

I am a newcomer in DSP. I am using MATLAB for that.My data is in form of a N*1 matrix. Why there is phase associated with it though its all real data(+ve integers). If i have some other data in N*1 matrix.How can i get effective crosscorrelation. My approach is:- --FFT --filter using simple filter to remove low frquency component --iFFt --obtain cross and auto correlation. Thanks in ...

## Convolution property of DFT

Started by in comp.dsp13 years ago 4 replies

Hi, I'm trying fast convolution property but there seems to be some mistake (with the answer). Here is the Matlab code for it, clear all;...

Hi, I'm trying fast convolution property but there seems to be some mistake (with the answer). Here is the Matlab code for it, clear all; clc; % Test Vector Convolution a = [1 2 3 4 5]; b = [10 20 30 40 50]; c= conv(a,b) A = [1 2 3 4 5 zeros(1,5)]; B = [10 20 30 40 50 zeros(1,5)]; d= ifft(fft(A) .* fft(B)) c - d(1:9) The results are: c = 10 40 100 200 350 ...

## ofdm RF portion doubt...

Started by in comp.dsp18 years ago 5 replies

Hi all i am basically from GPS doing usual Acuistion, tracking stuff for CDMA signal... recently moved in to ofdm... still...

Hi all i am basically from GPS doing usual Acuistion, tracking stuff for CDMA signal... recently moved in to ofdm... still learning..this site doing a great favour.. after going thorugh all basics i have few points to comment and ask.. 1. IFFT will genrate the complex valued signal,as input is output of QAM mapper and placement of carriers is assymetrical, how do we ...

## FIR EQ questions (simple ones)

Started by in comp.dsp17 years ago 6 replies

As promissed ... newbie questions... be gentle :-) Reading up on making FIRs by using the IFFT approach. E.g. setup your frequency shape...

As promissed ... newbie questions... be gentle :-) Reading up on making FIRs by using the IFFT approach. E.g. setup your frequency shape then do the inverse FFT, multiply by a suitable window and voila. In the examples they set the power to 1 (does that mean real = 1, imag = 0?) and all others to zero for the band they wanted. Could you set it to higher than one to amplify the band? ...

## Windows and "overlap and add"

Started by in comp.dsp18 years ago 26 replies

Just how flat need a window be to utilize "overlap and add" Window data -- FFT -- manipulate in freq domain -- IFFT -- add in time domain

Just how flat need a window be to utilize "overlap and add" Window data -- FFT -- manipulate in freq domain -- IFFT -- add in time domain