## Convolution and FFTW question.

Started by in comp.dsp9 years ago 8 replies

Seems dumb*, but what the hey: (data sets are 1D PCM audio data) Convolution is O(n*m) where n is the length of one vector to be convolved, m...

Seems dumb*, but what the hey: (data sets are 1D PCM audio data) Convolution is O(n*m) where n is the length of one vector to be convolved, m is the length of the other vector. Convolution using FFT is alleged to be O(n log(n))... *part of this is things I can't easily find in the FFTW docs. 1) The product of a DFT from FFTW is of the same length as the original PCM stream to which th...

## Derivative of convolution

Started by in comp.dsp14 years ago 5 replies

If y = conv(x,w) What is the derivative of y with respect to w ? Here y is the convolution between x and w, all are one dimensional....

If y = conv(x,w) What is the derivative of y with respect to w ? Here y is the convolution between x and w, all are one dimensional. Thanks This message was sent using the Comp.DSP web interface on www.DSPRelated.com

## Why linear convolution in OFDM causes ICI;

Started by in comp.dsp11 years ago 2 replies

Hello group We know that the use of cyclic prefix (CP) in an OFDM turns the linear convolution (between the channel and the transmitted...

Hello group We know that the use of cyclic prefix (CP) in an OFDM turns the linear convolution (between the channel and the transmitted signal) into a circular convolution. This is efficient to do because then we can easily equalize the channel. In most books it is referred that CP combats ISI and ICI. With ISI i am fine. I know that a circular conv between the channel (L points ) and...

## fastest convolution

Started by in comp.dsp14 years ago 18 replies

Hi, Does anybody have the fastest method (using paper and pencil) to calculate the convolution: y[n]=x[n]*h[n] where x[n]=u[n-3] -...

Hi, Does anybody have the fastest method (using paper and pencil) to calculate the convolution: y[n]=x[n]*h[n] where x[n]=u[n-3] - u[n-14], h[n]=u[n-5] - u[n-8], where u[n] is the step function, u[n]=1 for n> =0, and u[n]=0 for n

## why we want to do folding while performing convolution

Started by in comp.dsp13 years ago 34 replies

hi all can u explain in detail why there is need for folding when we perform convolution operation with an (practical)example? thanks in...

hi all can u explain in detail why there is need for folding when we perform convolution operation with an (practical)example? thanks in advance sk

## what priority does convolution "*" have? The same as multiplication?(dot?)

Started by in comp.dsp14 years ago 11 replies

Hi all, I am trying to evaluate some expressions consisting of: fg*hx*y where all letters denote function of time t. ie. f is f(t), y...

Hi all, I am trying to evaluate some expressions consisting of: fg*hx*y where all letters denote function of time t. ie. f is f(t), y is y(t), x is x(t), ... fg denotes function multiplication. g*h denotes function convolution. I want to figure out is the "convolution" the same priority as "multiplication"? ie. can I evaluate the above expression from left to right, or from...

## Buffer management for Overlap Add method of block convolution

Started by in comp.dsp9 years ago

I have an audio stream which arrives in blocks of length FRAMES. The processing function must return another block of length FRAMES as...

I have an audio stream which arrives in blocks of length FRAMES. The processing function must return another block of length FRAMES as the output. I have implemented an overlap add algorithm of block convolution to convolve a simple FIR filter of length M taps, zero padded to length N=L+M-1 where L is the size of the sub-block of convolution. My question is, how do I handle the final sub-bl...

## turbo, convolution codes, rate matching

Started by in comp.dsp6 years ago 10 replies

Sirs, I have few questions on turbo codes ... Followed by turbo coding is the rate matching stage where encoded data are dropped. Now, since...

Sirs, I have few questions on turbo codes ... Followed by turbo coding is the rate matching stage where encoded data are dropped. Now, since decoder operates like machine, will dropping of data not break the decoder algorithm? Another related question, what does convolution signify in case of convolution coding? Thanks, manish

## strange performance of convolution decoder for burst errors

Started by in comp.dsp13 years ago

Hi, I am deveoping a fec system. i am using convolution codes (K=7, code rate=1/2). i did some simulations in MATLAB to test...

Hi, I am deveoping a fec system. i am using convolution codes (K=7, code rate=1/2). i did some simulations in MATLAB to test convolution decoder's performance against burst errors. I took 128 bit frame of random data. Then used convenc function to encode it. and then introduced burst errors by selecting some bit randomly and making following bits zero (total number of consecutive bits which ...

## convolution with time-varying offset

Started by in comp.dsp5 years ago 3 replies

Hi all, I want to implement a convolution with timing offset in Matlab. My continuous signal equation is: r(t) = sum over k of...

Hi all, I want to implement a convolution with timing offset in Matlab. My continuous signal equation is: r(t) = sum over k of (a(k)*h(t-k*T-k*0.1*T)), where a(k)'s are a stream of bits, h is the pulse shape, and T is the symbol period. My sampled h is [1 4 6 4 1]. Could you please guide me how to do this? Thanks, Elnaz

## COnvolution and FFT

Started by in comp.dsp14 years ago 2 replies

Hello, I have a gaussian kernel of size [192,192] to be convoluted with an image of size [512,512] for smoothing. Using the FFT property that...

Hello, I have a gaussian kernel of size [192,192] to be convoluted with an image of size [512,512] for smoothing. Using the FFT property that fft of a convolution is the product of the fft of the individual terms (fft(f(t) * g(t))) = f(w)g(w), i could say that smoothedimage = fftinverse(fft(image) fft(kernel)) the problem i am encountering is this: straightforward convolution is easy b...

## FFT and time domain amplitude after FFT convolution

Started by in comp.dsp13 years ago 8 replies

I got a little problem when performing a FFT convolution. I try to have the output to have the same amplitude as it would with a...

I got a little problem when performing a FFT convolution. I try to have the output to have the same amplitude as it would with a time-domain convolution. To do so, I set the sum of the values of the samples of my kernel to 1.0, and after I FFT the kernel and the signal to convolve, I divide the values of both signals by the square root of the number of samples (which is the same since they...

## Convolution versus LPFiltering

Started by in comp.dsp15 years ago 28 replies

Hi everyone, I'm trying to implement a digital filter in c++ (assignment work, so I can't just use one that someone else has written...

Hi everyone, I'm trying to implement a digital filter in c++ (assignment work, so I can't just use one that someone else has written (--bummer)) and along the way I've discovered that my knowledge of (low pass) filtering isn't quite what it should be. I designed my filtering algorithm around convolution of two sequences, but when testing in Matlab I've come across an issue. %example code...

## Analog and Digital Convolution

Started by in comp.dsp4 years ago 13 replies

Hello, I have two digital signals that have to be convolved. Lets say we do that and get an output. If we then pass both these signals through...

Hello, I have two digital signals that have to be convolved. Lets say we do that and get an output. If we then pass both these signals through Digital to Analog converters (DAC) and convert both signals to analog and then perform convolution in continuous time will the output be the same? In other words what is the relation between a discrete time and continuous time convolution of two sig...

## Convolution relation

Started by in comp.dsp11 years ago 3 replies

I have a question about a particular relationship with convolutions. We want to transmit a particular waveform X, but through that process the...

I have a question about a particular relationship with convolutions. We want to transmit a particular waveform X, but through that process the input signal X gets convolved with some annoyance term H and we actually send Y. I.e. Y = H * X (where * = convolution) By knowing the X we want and the Y we actually end up with, our problem is to make a different input signal Z that ends up bein...

## complex convolution

Started by in comp.dsp14 years ago 3 replies

Dear All, I would like to convolve two complex sequences. Could anybody help me how to define the convolution of two complex sequences...

Dear All, I would like to convolve two complex sequences. Could anybody help me how to define the convolution of two complex sequences please? Thanks in advanced. Regard, nmaedewi This message was sent using the Comp.DSP web interface on www.DSPRelated.com

## Fast 2d convolution using FFTW

Started by in comp.dsp13 years ago 3 replies

Hi Community! I've got a problem that has been driving me mad for several days: I need a quick 2d convolution of a picture and a big (say...

Hi Community! I've got a problem that has been driving me mad for several days: I need a quick 2d convolution of a picture and a big (say 70x70) kernel. I was thinking of doing it in frequency domain using FFTW (the programme is in C++). This is the way I am doing it: 1. Pad the filter to the size of the input image. (padding "all around", so the "important" part is in the middle) 2....

## correlation v/s convolution?

Started by in comp.dsp10 years ago 4 replies

Is it true that the magnitude response remains same but only the phase response is different, between convolution and correlation? Bharat

Is it true that the magnitude response remains same but only the phase response is different, between convolution and correlation? Bharat

## Online convolution coefficient calculator...

Started by in comp.dsp13 years ago 1 reply

I seem to remember from my DSP days at uni that there is a java website somewhere that is able to calculate discrete convolution coefficients...

I seem to remember from my DSP days at uni that there is a java website somewhere that is able to calculate discrete convolution coefficients for a few simple filter types based on the required cut-off and sampling frequency. Anybody know of such a site? I also have a copy of Maple which I'm sure would make light work of such an elementary task. Nathan

## An operation "between" convolution and pointwise multiplication

Started by in comp.dsp10 years ago 4 replies

For the impatient, my question comes first, motivation for the question afterward. I started looking into the fractional Fourier transform....

For the impatient, my question comes first, motivation for the question afterward. I started looking into the fractional Fourier transform. Since a Fourier transform converts a convolution operation into a pointwise- multiplication, what can we say about a /fractional/ Fourier transform? If I transform "half way" between time and frequency, do I convert the convolution operation into somet...