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Post subject: Digital Aliasing Facts and Testing
Posted: Fri Jul 15, 2011 10:12 am
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Aspiring Musician
Aspiring Musician

Joined: Sun Jan 30, 2011 4:43 pm
Posts: 318
Whether you have fizz problems on your amp or not, I thought that some educational information about the subject might be of interest to some of you.

Since I have a MII and don't have a significant problem with fizz, it is hard to say if digital aliasing is entirely to blame for the problems on some III, IV and V models - it very well could be related to something else, I don't know, but aliasing is a likely culprit for at least some of the problems people are having.

Anyway, here are some links for those curious enough to surf them...

First, a Wikipedia artical on aliasing in general (it's not just audio related):

http://en.wikipedia.org/wiki/Aliasing

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More math than most mortals can bare, don't even think about clicking this if basic music theory makes your brain hurt...:

http://en.wikipedia.org/wiki/Nyquist%E2%80%93Shannon_sampling_theorem

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This artical explains the audio phenomenon explicitly in simple terms:

http://theproaudiofiles.com/digital-audio-aliasing-explained/

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While this artical is aimed at recording, it gives a pretty good overall description how aliasing problems can be avoided in recordings - this may be similar to how manufactures approach designing circuitry in modeling amps to address the problem:

http://www.mstarlabs.com/dsp/antialiasing/antial.html

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As you may know, other modeling amps and digital effects suffer from the problem. In this artical, the man responsible for the Axe-FX writes about the problem and compares his product with 2 other un-named modelers using verifiable testing (yes, even the $1800 Axe-FX can have fizz problems):

http://www.setbb.com/axefx/viewtopic.php?mforum=axefx&t=460&postdays=0&postorder=asc&start=0&mforum=axefx

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How Axe-FX users can minimize fizz (mostly not translatable to a Mustang... hmmm seems that Mustang parametric EQ effect I was wishing for would come in pretty handy):

http://forum.fractalaudio.com/axe-fx-general-discussion/32464-minimizing-fizz-buzz-patches.html

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In the 'A Study in Aliasing' artical linked above, the tests were done using an app called TrueRTA. Level 1 of TrueRTA is free unexpiring software, although it is limited to a resolution of no finer than one octave. This shouldn't be a problem for general curiosity testing purposes.

If you are a bit of a techy, you can get factual, verifiable and comparable scientific evidence. Users can compare just how bad the problem is in their particular amp with other users. Here is the link to TrueRTA:

http://www.trueaudio.com/rta_abt1.htm

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dude


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Post subject: Re: Digital Aliasing Facts and Testing
Posted: Fri Jul 15, 2011 6:31 pm
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Hobbyist
Hobbyist

Joined: Fri Mar 25, 2011 5:49 pm
Posts: 26
Thanks for the info... A really helpful post :) Believe me... I didn't read the really technical stuff.. .but interesting just the same...:)


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Post subject: Re: Digital Aliasing Facts and Testing
Posted: Fri Jul 15, 2011 7:05 pm
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Roadie
Roadie

Joined: Mon Feb 21, 2011 12:01 pm
Posts: 218
p90sdude,

Thanks for these links; I look forward to some light reading :lol: and hopefully I will learn something along the way.

Very kewl.

PITA


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