Old 01-31-2018, 10:45 PM   #1
kneelherring
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Default dither doesnt dither

in the render dialog, tested a 16-bit file peaking at -90db, lots of truncation noise
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Old 01-31-2018, 11:39 PM   #2
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adding noise is the principle of dithering/noiseshaping

you can use it to lower low volume noise in an otherwise normal leveled setting to bring out the lowlevel parts more clearly when renderng to a lower bitlevel (f.i. 32fp to 16bit).


test : make a low level (-90 dB f.i.) sinewave (js:generator and record output

render it to 16bit with and/or without dithering and import all four

normalize all of them

Before play reduce the overall volume

undithered unnoiseshaped will be the ugliest. Lots of artefacts, you "hear" the steps.

dithered noiseshaped will be the best result , at -90 all will be covered with noise of course, but the sinewave is much more pleasing

with dither and without noiseshaping will be second best, but the noise come out too much (of cause , it's not shaped)

without dither with noiseshaping will be nearly as "ugly" as the one without all at a little lower volume (if cause, the noise is shaped and more earpleasing)
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Old 02-01-2018, 12:49 AM   #3
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specifically, with the dither in the render dialog enabled, truncation noise is present
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Old 02-01-2018, 01:43 AM   #4
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and without dithering truncation noise is gone?
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Last edited by bobobo; 02-01-2018 at 02:06 AM.
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Old 02-01-2018, 01:54 AM   #5
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without truncates, as it should
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Old 02-01-2018, 03:05 AM   #6
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i'm too dopey to understand the problem
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Old 02-01-2018, 03:14 AM   #7
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it looks like Reaper uses Gaussian dither...it does not perform as well as TPDF (on test signals) unless you use the noise shaping option.
TPDF FTW !
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Old 03-03-2018, 11:22 AM   #8
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should this be addressed?
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Old 03-03-2018, 11:31 AM   #9
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Can you explain how we can test and verify the bug?
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Old 03-03-2018, 11:53 AM   #10
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This is not a bug, just the type of dither used.
They should offer options for dither, like the JS dither plug in has.
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Old 03-03-2018, 12:24 PM   #11
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REAPER's dither is not guassian btw. https://forum.cockos.com/showthread.php?t=23324
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Old 03-03-2018, 12:51 PM   #12
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Huh, then maybe it is a bug because it acts just like Gaussian and not like TPDF...
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Old 03-03-2018, 01:08 PM   #13
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Maybe what you are observing is just the fact that the dither is 1.5 bits which is on the lighter side -- adding less noise energy at the expense of possibly letting truncation noise through for certain highly structured or degenerate sounds. It's unlikely there is a bug in REAPER's dither.
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Old 03-03-2018, 01:37 PM   #14
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stated as a bug simply because removal of truncation noise (distortion) is not absolute, which is the reason for dither in the first place. tpdf with a noise floor of -90.4 (16-bit) is what's needed imo
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Old 03-03-2018, 04:11 PM   #15
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Just for my own education: how do you distinguish truncation- from statistical noise in the final waveform ?

(Please don't say "by your ears". I will not accept this as a way of pin pointing bugs.)

Same question goes out for Gaussian noise vs TPDF.

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Old 03-04-2018, 03:52 AM   #16
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Quote:
Originally Posted by schwa View Post
Maybe what you are observing is just the fact that the dither is 1.5 bits which is on the lighter side -- adding less noise energy at the expense of possibly letting truncation noise through for certain highly structured or degenerate sounds. It's unlikely there is a bug in REAPER's dither.
Yeh, I was drawing conclusions based on one test.
I just saw something less dense than TPDF so I ASSumed it was Gauss...
Thanks for clarifying.
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Old 03-05-2018, 12:13 AM   #17
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https://www.dropbox.com/s/3v123v84ov...led-1.png?dl=0[

-90db sine 440hz

1- flat tpdf
2- built in dither
3- truncation
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Old 03-05-2018, 05:37 AM   #18
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What you're seeing is the "lightness" of the dither. A clean sine wave is a highly structured signal, so truncation noise is maximized, and 1.5 bits of noise doesn't quite mask it. This is a degenerate case.

Having said that, we could add a setting for dither bit depth in the render dialog, for people who want to add more noise.
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Old 03-05-2018, 07:46 AM   #19
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Wellllll, it turns out the current render dither is 1 bit, not 1.5. We'll just change this to 1.5 bits where it was supposed to be in the first place. Thanks for the post.
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Old 03-05-2018, 09:03 AM   #20
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it would be great to see the kneelherring diagram for that

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Old 03-05-2018, 09:20 AM   #21
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Quote:
Wellllll, it turns out the current render dither is 1 bit, not 1.5.
^Oh-- ""so highly trained that he can type code that compiles correctly almost 3% of the time. "" - if you wanted a presidency--1 must increase this range to at least 5%!
How about a whole range of dithers?? for those that like to fool around-- just being dithering idjutzz..
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Old 03-05-2018, 09:43 AM   #22
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If interested ... AIRWindows makes a whole collection of DITHER plugins.
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