dithering

[SumAnuT]

http://www.tonmeister.ca/main/textbook/node593.html

There are a couple of characteristics of this error that we should discuss. Firstly, because the sine wave repeats itself, the error signal will be periodic.


To moze da se desi samo kod sinusoide i ostalih prostoperiodicnih signala.
Kod slozenog audio signala, greske ne mogu biti periodicne, jer je signal slozen tj. nije prostoperiodican tj. greske ce uvek biti nasumicne i nece se uvek ponavljati istim redom.


Sad vidim da je velika greska sto su nas uopste ucili da se kaze kvantizacioni sum, kada to ustvari i nije sum, vec distorzija ...

[SumAnuT]

Evo odgovora i na arturovo pitanje:

I once attended a seminar on digital audio measurements given by Julian Dunn. At lunch, I sat at a table of about 12 people, and one of the other participants asked me the simple question ``what do you think about dither?'' I responded that I thought it was a good idea9.1. Then the question was re-phrased - ``yes, but when do you use it?'' The answer is actually pretty simple - you use dither whenever you have to re-quantize a signal. Typically, we do DSP on our audio signals using word lengths much greater than the original sample, or the resulting output. For example, we typically record at 16 or 24 bits (with dither built into the ADC's), and the output is usually at one of these two bit depths as well. However, most DSP (like equalization, compression, mixing and reverberation) happens with an accuracy of 32 bits (although there are some devices such as those from Eventide that run at 64-bit internally). So, a 16-bit signal comes into your mixer, it does math with an accuracy of 32 bits, and then you have to get out to a 16-bit output. The process of converting the 32-bit signal into a 16-bit signal must include dither.

Remember, if you are quantizing (or re-quantizing), then you dither - every time.

http://www.tonmeister.ca/main/textbook/node596.html

Ceo sajt je vredan paznje: http://www.tonmeister.ca/main/textbook/node596.html

[boggy]

Originally Posted by SumAnuT

....

To moze da se desi samo kod sinusoide i ostalih prostoperiodicnih signala.
Kod slozenog audio signala, greske ne mogu biti periodicne, jer je signal slozen tj. nije prostoperiodican tj. greske ce uvek biti nasumicne i nece se uvek ponavljati istim redom.
......

Nemoj meshati shum i muziku. Koliko god sve to tebi izgledalo "nasumicno", i dalje je daleko od slucajnog... kako god okrenes, kvantizacione pojave ce imati neku "zakonitost" pojavljivanja daleko uredjeniju nego sto je beli shum...

A da se kvantizacioni shum moze nazvati i kvantizacionom distorzijom, pa ok.. moze... kako hoces... samo je bitno da se razumemo.... nebitan je naziv.

Isto tako uzmi u obzir da je Bota ovde spomenuo samo veoma uproscenu harmonijsku analizu, primenjivu na periodicne signale, da bi lakse objasnio....
nadogradnja te analize sa lakocom moze da se generalizuje i na slozeno periodicne ili aperiodicne signale, kakva je najcesce muzika.... rezultati analize bi dali iste rezultate... samo sto bi smetnja koju pravi kvantizacija bila takodje aperiodicna kao i audio signal,.. ali vrlo slicna tom audio signalu.. modulisana, pomerena na frekventnoj osi.. medjutim.... sasvim prisutna i mnogo razlicita od belog shuma....


pozdrav

bogi

[SumAnuT]

Evo nadjoh i kod ovog lika da je periodican ...
Ako ih ne mozes pobediti, pridruzi im se, nista mi drugo ne preostaje
Izvinjavam se sto nisam verovao.

Since the quantization error is periodic, it is a distortion of the signal and is therefore directly related to the signal itself. Our brains are quite good at ignoring unimportant things. For example, you walk into someone's house and you smell a new smell - the way that house smells. After 5 minutes you don't smell it anymore. The smell hasn't gone away - your brain just ignores it when it realizes that it's a constant. The same is true of analog tape noise. If you're like most people you pay attention to the music, you stop hearing the noise after a couple of minutes. Your brain is able to do this all by itself because the noise is unrelated to the signal. It's a constant, unrelated sound that never changes with the music and is therefore unrelated - the brain decides that it doesn't change so it's not worth tracking. Distortion is something different. Distortion, like noise, is typically comprised entirely of unwanted material (I'm not talking about guitar distortion effects or the distortion of a vintage microphone here...). Unlike noise, however, distortion products modulate with the signal. Consequently the brain thinks that this is important material because it's trackable, and therefore you're always paying attention. This is why it's much more difficult to ignore distortion than noise. Unfortunately, quantization error produces distortion - not noise.

Zbog ovoga sto je covek napisao sam rekao da je pogresno sto su nas ucili da je to sum, jer kao sto covek rece, sum se ne menja, te mozak prestane da obraca paznju kroz neko vreme, a distorzija se menja, tj. modulise u zavisnosti od signala, pa je mozak stalno prati, zato se i dodaje sum, da bi mozak mogao da se opusti i slusa muziku.

[Bota]

Upravo to. Degradacija signala kod D/A konverzije je neminovna. Hajde onda da promijenimo karakter te degradacije pa da ona ne bude korelisana sa signalom (da bude nezavisna od signala) da bi je mozak mogao percipirati kao šum.

To se postiže dithering-om.