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Ditherómy explanation of how it keeps details below quantization level, Was: "Dither" (TOS #6)
KMD
post Mar 7 2012, 13:22
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To help with the understanding of dither, I am posting an explanation, of how signal details smaller than the quantization level are retained, after quantization, when Dither Noise is added to the source material.
A small signal detail with height less than the quantization level, and centred half way between two quantization steps, is too small to cross a quantization step. It is lost when the waveform is quantized. With a Dither Noise waveform added, the height of the two waveforms summed is occasionally greater than the quantization level. At these occasional points the waveform crosses a quantization step. So now when this waveform is quantized, although the result is noisy, the shape of the original signal detail is retained.
Discussion invited.
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greynol
post Mar 21 2012, 21:14
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In light of the recent conversation over the quantization grid, I humbly request that knowledgeable people review our wiki article on dither:

http://wiki.hydrogenaudio.org/index.php?title=Dither

After a quick review I really must question the emphasis that is placed on how dither affects the visual appearance of waveforms. This is clearly not in line with one of the most important tenets of our forum

This post has been edited by greynol: Mar 21 2012, 22:09


--------------------
Your eyes cannot hear.
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mjb2006
post Mar 22 2012, 01:57
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QUOTE (greynol @ Mar 21 2012, 14:14) *
After a quick review I really must question the emphasis that is placed on how dither affects the visual appearance of waveforms. This is clearly not in line with one of the most important tenets of our forum


The article I had started last year was just edited rather heavily about a week ago by KMD, as per his post above. I do appreciate that someone besides me put some effort into it, but aside from the addition of the questionable content greynol mentioned, several details that I don't think should've been removed were cut out.

For example, my original text for the first paragraph:
QUOTE
Dither is random or semi-random noise added to a signal in order to mask quantization noise and/or extend dynamic range. The simplest dither is quiet white noise, but more complicated forms of dither are possible using [[noise shaping]], and they can even be completely inaudible.

...is now this:
QUOTE
Dither is random noise added to a signal in order to increase the degree to which the quantization and sampling process accurately reproduces the image of the input signal. The simplest dither is quiet white noise, but more complicated forms of dither are possible using [[noise shaping]].


...and most of the text (the bold part) adapted from a post by Andy H-ha was completely removed:
QUOTE
Going from 24-bit to 16-bit, the quantization error is very small and the distortion/noise is extremely unlikely to be heard in any real music. Since quantization error isn’t audible in any real music at useable listening levels, whether dither must be used is more a matter of doctrine than functionality.


Other changes were made as well. It's possible some of this was done to give the appearance of neutrality, requiring claims about dither's inaudibility to be backed up, but I wanted that stuff in there because it's important to know while it's easy and common for dither to amount to "audible white noise", it need not be white/totally-random nor audible (especially for the common 24-to-16-bit conversion scenario). Besides, my understanding is that the onus is on the person claiming that something is audible, i.e. that there's a difference, not on the person who says there's not. I'm not saying what I wrote was perfect, but surely there's some middle ground.

This post has been edited by mjb2006: Mar 22 2012, 02:02
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saratoga
post Mar 22 2012, 02:05
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Obviously someone who doesn't understand sampling should not be editing the wiki entry on dithering, so I've reverted those changes. Still, some editing of the page would be nice.
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Posts in this topic
- KMD   Ditherómy explanation of how it keeps details below quantization level   Mar 7 2012, 13:22
- - icstm   QUOTE (KMD @ Mar 7 2012, 12:22) To help w...   Mar 7 2012, 13:29
- - pdq   You might add that even when that small signal DOE...   Mar 7 2012, 15:07
|- - Paulhoff   QUOTE (pdq @ Mar 7 2012, 10:07) You might...   Mar 8 2012, 19:03
- - KMD   icstm - Thanks pdq - true, that is another funct...   Mar 7 2012, 16:10
- - icstm   Spatial dither: In a video feed spatial dither can...   Mar 7 2012, 17:43
- - mjb2006   Please do what you can to improve our wiki article...   Mar 7 2012, 21:43
|- - Notat   QUOTE (mjb2006 @ Mar 7 2012, 14:43) Pleas...   Mar 22 2012, 15:38
- - NullC   I highly recommend the first few sections of this ...   Mar 8 2012, 17:39
|- - icstm   QUOTE (NullC @ Mar 8 2012, 16:39) I highl...   Mar 9 2012, 16:14
- - KMD   Paulhoff - You were probably getting the benefi...   Mar 8 2012, 19:12
- - KMD   NullC - If you put fig 2.4, 2.5 ,2.11, 4.6 in...   Mar 8 2012, 19:15
- - KMD   Reference for this subject. Paper titled, ...   Mar 8 2012, 20:05
- - KMD   mjb2006 - Will do   Mar 9 2012, 15:24
- - greynol   In light of the recent conversation over the quant...   Mar 21 2012, 21:14
|- - mjb2006   QUOTE (greynol @ Mar 21 2012, 14:14) Afte...   Mar 22 2012, 01:57
|- - saratoga   Obviously someone who doesn't understand sampl...   Mar 22 2012, 02:05
- - benski   I remember the first lab in University Physics cla...   Mar 21 2012, 21:42
- - 2Bdecided   Important points: Dither removes the potentially ...   Mar 22 2012, 11:38
- - alanofoz   Warning: very shallow & not very scientific: ...   Mar 22 2012, 12:05


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