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what are the appearance of aliasing in image and audio processing?

Hi all, I've heard a lot of aliasing. What do they look like in image and audio/speech/music with aliasing? I did not see/hear any real aliasing stuff, so the concept of aliasing looks abstract to me, although I know how it occurs in terms of mathematics... I am also wondering about the ...

Re: Interpolation

On Tue, 1 Apr 2008 23:35:21 -0700 (PDT), dbd wrote: > "Get over it" is not an attitude. It is a constructive suggestion for > someone who has difficulty perceiving the use of "anti-aliasing > filter" for filters that perform anti-aliasing. > > I'm not annoyed, I'm disappointed. > > I'v...

2 tone IMD aliasing on Win Mobile

Looks like Treo and maybe other Windows Mobile based devices have huge (~15% THD) wideband aliasing products when you play any non 44.1 file ( MP3 or .Wav) back. Windows resamples all to 44.1 k and seems to have poor anti-aliasing filters. Whats up with that? My Laptop (XP) AC97 is OK on ...

Does an inadequate pixel-density cause spatial aliasing?

Hi: Is spatial aliasing caused by an insufficient pixel-density? Also, some video websites say that spatial aliasing causes jaggies, other say it causes the Moire effect, still others say it causes pixelation. Who is right? Thanks, Radium ...

Cascaded Integrator Comb and aliasing experts please help!

Please refer to www.intersil.com/data/fn/fn3651.pdf page 10 top and page 9 bottom. Please correct me if I assume something wrong. On figure 12 (pg 10) you see the aliasing profile of the CIC and how it does it translate to baseband. The filters performance can therefore be estimated. Quit...

What is the analog equivalent of aliasing?

Hi: Aliasing is a digital entity. What is the analog equivalent of aliasing? Thanks, Radium ...

Average the averages

I am making an application where several inputs has to be filtered. The filtering is a simple moving average filtering with a variable filter length. The problem is what happens when I connect these moving average filters in cascade? I know that I will get some aliasing, but how big is the aliasing ...

Question about aliasing spectrum in RC filter

Hi, For a single carrier system, rooted raised cosine pulse shaping filter is generally used in both transmitting and receiving. I have read a paper which said the FFT bin outside of signal plus excessive bandwidth were set to zero to suppress aliasing signal component. I find that in frequency...

Re: Length of signal vs. frequency resolution

M.L. wrote: > Hello Jerry, > > I am not sure what you mean.. Why will the effect that you describe be > introduced? It's called "aliasing". see http://www.dsptutor.freeuk.com/aliasing/AliasingDemo.html Jerry -- Engineering is the art of making what you want from things you can ge...

Anti-Aliasing filter

If you are estimating time-delay bewteen two microphones would it be better to use a Bessel filter for anti-aliasing rather than a Butterworth due to the approximate linear phase. Wang King ...

automatic detection of aliasing?

Hi all, I need your help on the following difficulties: I am designing something like "automatic" detection of aliasing, programmatically. For a given signal discrete time signal x(n), possibly infinite support, we know its values are all positive, they are absolutely summable, so DTFT ...

How to prevent aliasing caused by non-linear function implemented in the digital domain

How to prevent aliasing caused by non-linear function implemented in the digital domain Consider an audio input signal band limited to 20 kHz and sampled at 44.1 kHz for example. No problem. But suppose I want to implement a limiter or other non-linear function in the digital domain. The ...

samplig rate conversion

I have a large bunch of WAV files sampled at 44.1kHz and at 48kHz, which I would like to convert to 8kHz sampling rate, efficiently/quickly but professionally & accurately (i.e. no aliasing etc.) Could anyone recommend me a tool for doing that (free software or Matlab)? (For example I know...

Why is it bad to have spectral samples nonzero at fs/2?

I'm working on a paper about interpolation that I threatened to do long ago. I'm trying to say that a spectrum that has nonzero (or not small) samples at or near fs/2 is problematic. But I'm having a bit of trouble saying why it's bad necessarily. One thing one can say is that it's likely t...

aliasing condition for radon transform?

I am talking about geophysical data here, where you have a record consisting of a few hundred traces, so the data has two dimensions time and distance (or t-x in short). If an event has a dip or slowness less than one sample per trace, it is not aliased. If it has greater dip, it would alias, u...

zero padding avoids aliasing

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...

Interesting example of aliasing...

Got this from a friend, who was mostly interested in it because it looks cool, and we both play an on-line game that includes this type of helicopter. http://www.break.com/index/helicopter-blades-stop-moving.html It's a pretty interesting example of visual aliasing. I wonder what the rota...

Spatial Aliasing in Beamformers

I have been reasing a paper that says that for acoustic beamformers (I suppose the same applies to EM beamformers), the distance between microphones must be d ...

Sound Card Question

How does a sound card set its anti-aliasing filters? After all, you can program a sound card to read at say 44.1kHz or 22,050Hz or half of that again so how do the ani-aliasing filters change? Switched cap filters are sampled filters so they would not be good and digital filters are no good eith...

A Basic Aliasing Question

Here's something I don't remember about aliasing - someone please verify whether or not this is correct. Assume the sample rate is 2000 Hz for the sake of illustration. Conventional wisdom tells us that a 1200 Hz signal will look like an 800 Hz signal due to aliasing. I say it may look the s...

How I can design real time dsp system

Hello everyone, I want to design a real time DSP system.Band of interest extends from o to 4kHz.I will use 12 bit ADC and 3rd order butterworth lowpass filter. What I want to know is how I can estimate the minimum stopband attenuation for the anti-aliasing filter, minimum sampling frequency an...

Re: Interchanging FIR and Decimation operation

> That is correct, you can't. I would question whether a length = 3 > filter is going to do you much good for decimating data by a factor of 8 > -- you would at least need a length = 8 filter and probably more. I forgot to mention one more thing abt the filter. It is not normal anti-aliasi...

Re: shift theorem for real valued signals

banton wrote: > Mmh.. allright. So the answer to the question, if I can use the > shift theorem to achieve arbitrary phase shifts for real valued > signals is "NO!"? You can use a form of the shift theorem for arbitrary non-integer shifts. However, there is a complication that arises for...

Re: Oversampling and the FFT

Two additional thoughts. If there is noise in the adc, then sampling at a higher rate will cause that noise to be averaged over three samples rather than just the one. This might improve the snr a little. A long time ago Crystal (now Cirrus Logic) shipped two different versions of their aud...

Re: DSP Implementation Woes

> My apologies for the bad link....it is actually: > > http://s188.photobucket.com/albums/z65/liznbren/stuff/?action=view¤t=envelope.jpg > > Thanks.... > Brendan > > If I sample at just fractionally above the Nyquist rate, That is the problem right there, and what you are seein...

wavetable synth & anti-aliasing

hello, i'm trying to program a wavetable-based synth in c++. I have some waveforms and different envelopes for them and want to switch between settings while playing. I use a 4096 samples buffer. My question is, how do i now implement anti-aliasing? I thought of multiplying envelope & waveform, ...

Re: Filter design.

The amount of the distortion due to aliasing equals to the sum of power for all components higher then Fs/2. Indeed the speech spectrum envelope falls at about 12dB/oct at high frequencues. The amount of the high frq content in the clear voice is very low. So just the direct sampling at...

Downsampling by 2: What happens the Spectrum? (Not the Fourier Transform).

Given a stationary discrete-time stochastic process x(n) with discrete-time Fourier transform X(e^jw) and spectrum Sx(w). If x(n) is downsampled by two to give y(n) it is well known that Y(e^jw) = 0.5 [X(e^jw/2) + X(e^j(pi+w/2))]. (A) My question is, what is the resulting spectrum, not just...

Downsampling by 2: What happens the Spectrum? (Not the Fourier Transform).

Given a stationary discrete-time stochastic process x(n) with discrete-time Fourier transform X(e^jw) and spectrum Sx(w). If x(n) is downsampled by two to give y(n) it is well known that Y(e^jw) = 0.5 [X(e^jw/2) + X(e^j(pi+w/2))]. (A) My question is, what is the resulting spectrum, not just...

Re: Interpolation

On Tue, 01 Apr 2008 14:41:06 -0600, jim wrote: > Eric Jacobsen wrote: > > The more fundamental issue as I understand it, is whether or not a > > filter would change the original, uninterpolated input samples in the > > output, i.e., are the interpolated samples distinguishable from ...

Perceived aliasing in small ratio SRC

I'm pretty new to the world of frequency domain as proven by this question: Is there any correlation between the quality of resampler required to make aliasing "imperceptible" and the magnitude of sampling rate change? I'm currently playing with various resampling algorithms, running some 44...

Signal processing of the human visual system?

Ok first post here and I thought I'd bring up something that might be thought-provoking... have you ever looked at the workings of the human visual system? It does some fairly amazing things that, on the surface, seem to violate sampling theory. #1 - Hyperacuity In the eye, rods and cones ar...

Re: Examples of Anti-Anti-Alias Requirements

Tim Wescott wrote: > I'm trying to think of examples where using an anti-alias filter is a > bad idea, or must at least be approached with extreme caution. I > already know about control systems and video applications, and I believe > that this is a big issue with EKG machines. > > Do...

Re: Sound Card Question

"HelpmaBoab" wrote in message news:ph6Pf.4437$JZ1.96604@news.xtra.co.nz... > Are you saying that a SB has a fixed anti-aliasing filter at 20kHz even > you > you sample at say 22050Hz? Surely not. > I understood they used over-sampling and down-sampling. If I record from, say, an SB ...

Re: MDCT

hibhanu@gmail.com wrote: > Can anyone explain me How is MDCT different from basic DCT? how does > MDCT achieve Time Domain Alias Cancellation ( TDAC ) which is useful in > MPEG AUDIO compression. The MDCT *is* a DCT, a type-IV DCT to be precise (the "basic" DCT is type II), except that th...

Re: Physical significance: Replications of analog signal in digtial domain

Brad Griffis wrote: (snip) > From reading your posts it seems that you subscribe only to what I referred > to as "interpretation 2." However, BOTH are legitimate mathematical > interpretations. In order to properly interpret the DFT it is important to > have knowledge of your input...

decimation and anti-aliasing

Dear all, Thanks for all your replies but I am still a bit confused. Let me try rephrasing my question so that everyone gets a better picture of what I am trying to do. I have a large number (order of 10^13) of discretized data samples. I have to obtain the frequency spectrum of this data so that...

Re: Basic question on upsampling/downsampling

moe wrote: > Hi, I am new to DSP and learning about sampling and related topics. I have > read a book and visited online sites but still am having problems > understanding : > > 1. Why do we need a filter (FIR) BEFORE we downmsample when we perform > decimation. I understand why fo...

Shannon limit question

I read that band limiting the input to an A/D eliminates aliasing. I also read that using a very high sampling rate makes that filter very simple. Suppose I: 1. filter with a single stage low pass RC filter with 3db pint at .5 MHz 2. sample at 44.1 MHz 3. do simple sample rate conversion b...

Re: obtaining continuous time signal bin energy

Andor writes: > Randy Yates wrote: > > Andor writes: > > > Fs/2 stays right there. > > > > Really? Then why does sin(n*pi) disappear? > > That's not aliasing. I agree - it is not aliasing. But neither is it "staying right there." I trust we both know what we're talki...