## Forums Search for: Aliasing

## Newbie question

inI have a 2d signal (an image, actually) of which I want to calculate ACF. I tried to use the IFFT/FFT approach, but when I rotate the image...

I have a 2d signal (an image, actually) of which I want to calculate ACF. I tried to use the IFFT/FFT approach, but when I rotate the image I notice some strange effects (something aliasing-like). So I tried to pad my image both vertically and horizontally with zeros, doubling its dimension before calculating the FFT. Am I doing right? Someone can help me? Thank you Lorenzo

## bypassing antialiasing filter of TLV320AIC23

inHello, I have been using C6713 DSK. My question is; Is there antialiasing filter in front of AIC23 codec of DSK. If yes, can bypass...

Hello, I have been using C6713 DSK. My question is; Is there antialiasing filter in front of AIC23 codec of DSK. If yes, can bypass (omit, cancel) it? In other words, can I sample over 48 kHz frequencies with aliasing intentionally.

## Best FIR Coefficients for multirate app

inHello for this newbie question! I'm on developing a simple audio-sequencer application. So, if I want to play a 44100Hz samplesound with a...

Hello for this newbie question! I'm on developing a simple audio-sequencer application. So, if I want to play a 44100Hz samplesound with a default note at D4 like a drum at lower notes like C4,F3,E3,etc., I have to decimate to the according sampling-rate. But of course, to prevent aliasing, there must be a lowpass filter before decimation. The best way to to this very efficient is an FIR-...

## image subsampling problem???

inDear all, I want to ask how to downsample an image and avoid aliasing? How to make sure that an downsampled image can be reconstructed...

Dear all, I want to ask how to downsample an image and avoid aliasing? How to make sure that an downsampled image can be reconstructed perfectly? I guess I am too acquainted with time as my x-axis, now when it comes to 2D spatial domain, I get perplexed... Can anybody give me some enlightenment? Thanks a lot, -Walala

## Analyzing an "undersampled" sequence

inPerhaps I should post this elsewhere but we speak the same language here. I may have asked a similar question some time ago but now I have a...

Perhaps I should post this elsewhere but we speak the same language here. I may have asked a similar question some time ago but now I have a new perspective and want to investigate. I have a wastewater process that's being sampled periodically (uniform sampling for what it's worth). The sample rate is way too low to avoid aliasing but the samples are real enough and the data is contin...

## Aliasing - A new perspective out of Box

inHI all, Thank you very much for the participants in " Negative Frequencies" Thread. Here is another question from me. Yesterday I was...

HI all, Thank you very much for the participants in " Negative Frequencies" Thread. Here is another question from me. Yesterday I was watching a movie. In that, hero was chasing villain in a BMW car at a speed of 100 Miles/Hr.I was observing the car keenly and suddenly it appeared that the tyres of the car are rotating at only 8 miles/hr(I didnt measure..felt that its RPM is very less)...

## FFT: Could you help me to clarify some doubts?

inHello I should calculate a FFT of signal that have max 500Hz of frequency. I know that for avoid aliasing problem I must have a sample rate of...

Hello I should calculate a FFT of signal that have max 500Hz of frequency. I know that for avoid aliasing problem I must have a sample rate of Fmax*2, so I have fix it to: Sample_Rate_Frequency= 1024Hz Question 1) Is correct the follow table: [Acquisited Point] [Acquisition Duration] [Frequency Resolution] 1024 1 sec 1H...

## PCM 3003

inDear All Anybody knows how to change the sampling rate of PCM3003(Daughter Card for C6711 DSK card), it is 48Ksps and I need to work with...

Dear All Anybody knows how to change the sampling rate of PCM3003(Daughter Card for C6711 DSK card), it is 48Ksps and I need to work with 8ksps, apparently it has internally anti aliasing and post processing filter for 48Ksps. Thanks: Hamid

## producing odd&even harmonics

inHi, This is a little bit a repost but i have some new information now. I'd like to produce harmonics in a signal. Using the chebychev...

Hi, This is a little bit a repost but i have some new information now. I'd like to produce harmonics in a signal. Using the chebychev polynomials, you can produce individual overtones (1,2,3th, 4th, ... harmonic ) where T1(x) = 1; T2(x) = x T_n(x) = 2xT_{n-1} - T_{n-2}. But how to produce the undertones? Can i base myself on aliasing for this effect? how pls? Help ap...

## zero padding avoids aliasing

inhey guys - i can't seem to find find this statement any where - but it makes sense to me - could someone please verify. When you find the DFT of...

hey guys - i can't seem to find find this statement any where - but it makes sense to me - could someone please verify. When you find the DFT of a signal say: x[0]=2, x[1]=4, x[2]=6, x[3]=8 - you will get four discrete points in frequency (per period) now if you zero pad such that tou get x[0]=2, x[1]=4, x[2]=6, x[3]=8 x[4]=0, x[5]=0, x[6]=0, x[7]=0 - you will once agin get four discrete frequenc...

## OT:Sampling in Stats

inWhen the Stats people sample data for analysis they have a load of rules for population size etc. However, they never have to filter the data...

When the Stats people sample data for analysis they have a load of rules for population size etc. However, they never have to filter the data first to avoid aliasing. Is this because the data is already in "digital" format? Hardy

## Got it to work :-)

Hello all. I'm very happy to say my filter is working perfectly. What it looked like before was that I was aliasing input frequencies above...

Hello all. I'm very happy to say my filter is working perfectly. What it looked like before was that I was aliasing input frequencies above Fs/4 the decimating Nyquist. After much trial and error I think my problem was that 1. I didn't account for the filter gain - after filtering - the skirts then were heavily amplified. 2. I may have not added in correctly the previous MAC. (time for vers...

## Frequency Domain represeatation

inGuys: Why do the charts of the textbook representing the frequency response of a filter always show the range from -pi to pi instead of from 0...

Guys: Why do the charts of the textbook representing the frequency response of a filter always show the range from -pi to pi instead of from 0 to 2pi? If use the range from 0 to 2pi, examples in the chapter 2 of Understanding Digital Processing by Lyons would cause big problem. The sampling replication would shift to the right and aliasing explaination failed. Why "-pi to pi" not "0 to 2pi...

## antialiasing and decimation

inHi, is there a way to decimate a signal (reduce sampling rate) reducing aliasing without implementing a computationally intensive...

Hi, is there a way to decimate a signal (reduce sampling rate) reducing aliasing without implementing a computationally intensive low-pass filter? Consider that this signal is supposed to have frequency components higher than the reduced sampling rate. thanks

## Phase in FIR

inHi, I'm trying to specify a DSP system to measure a two sine waves around 100kHz and their resulting harmonics down to the 5th. The phase...

Hi, I'm trying to specify a DSP system to measure a two sine waves around 100kHz and their resulting harmonics down to the 5th. The phase information is important as well as the magnitude of the harmonics. In order to avoaid any aliasing and phase problems with an analog filter I 'm intending to oversample at 4MSPS. From what I can tell I will then need to perform a low pass FIR bef...

## Acoustic Beamforming Question

inI always assumed that sensors for a beamformer had to be spaced at least lambda/2 (half a wavelength) apart else we get spatial aliasing. Is...

I always assumed that sensors for a beamformer had to be spaced at least lambda/2 (half a wavelength) apart else we get spatial aliasing. Is this true for acoustic arrays too? I have seen papers on small arrays (circular say) for mobiles and such like. Let us asume that the mics are 1cm apart giving a wavelenth of 0.02m and a frequency (min) of 16.5kHz. Not much use is it? Hardy

## 10MHz signal sampling - which DSP?

inHello, i would like to process an analog signal, coming out from a photodiode with a maximum frequency content of 7-10MHz. Here my idea...i...

Hello, i would like to process an analog signal, coming out from a photodiode with a maximum frequency content of 7-10MHz. Here my idea...i don't know if it is something correct or not... i need your help... 1. A/D conversion, trying to aversampling the signal (at least 40-50MSPS) - anti aliasing filter to be evaluated (9-10 bits are enough) 2. CPLD of small FPGA after the DAC (maybe a Ma...

## QMF filter Order

Hi, I have read in many books that the order of the filters used in QMFs should be odd to satisfy the aliasing canceling condition. Can...

Hi, I have read in many books that the order of the filters used in QMFs should be odd to satisfy the aliasing canceling condition. Can anyone explain how the filter order is related to the above mentioned condition. Thanks

## Pitch shifting question

inHi. I want to do some pitch shifting of some samples I have. I'm trying to avoid the whole sample rate conversion problem. I can hack up...

Hi. I want to do some pitch shifting of some samples I have. I'm trying to avoid the whole sample rate conversion problem. I can hack up the hardware some. Q: Can I just alter the clock and rate that I send data to my DAC *WITHOUT* changing the anti-aliasing low-pass and accomplish my goal? Thank you. Henry.

## Re: Interpolation

inEric Jacobsen wrote: > > On Wed, 02 Apr 2008 07:27:42 -0600, jim > wrote: > > > > > You are asking if a filter designed...

Eric Jacobsen wrote: > > On Wed, 02 Apr 2008 07:27:42 -0600, jim > wrote: > > > > > You are asking if a filter designed to prevent aliasing is really an > > > > anti-alias filter. How much of an answer do you want to a question like > > > > that? > > > > > > It's the same sort of question of whether or not an upsampling filter > > > should be called an inte