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I work in Pro Tools (as I know it Pro Tools works internally with 32-bit flot) and will bounce my mix to a 24-bit file. I want to apply dither using a plugin.

However, there's no dithering for 24-bit targets in the POW-r dithering plugin, only 16-bit and 20-bit. Can I use the 20-bit dithering when I bounce to a 24-bit target, or do I need to find a plug that has a dithering noise specifically for 24-bit targets?


Note: I know there's an ongoing debate about whether dithering is needed when bouncing to a 24-bit target ... but let's not take that discussion here and now ;)

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The idea of dithering is to enhance the signal, making the signal more accurate in the band of frequency we are the more sensitive. This doesn’t reduce the overall quantization noise, but shifts it where our ears are less sensitive.

If you apply a 20bits dithering to a 32bits audio stream (24 bits of relative precision, the size of the mantissa), you reduce the precision from around 24 bits to a little above 20 bits. You add quantization noise on all frequencies : it is not what you would want to do, it is near the opposite.

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  • Would be nice with some clarifications: "you reduce the precision from around 24 bits to a little above 20 bits" -- how is that? "You add quantization noise on all frequencies" -- doesn't dithering always add noise on all frequencies? Oct 27 at 14:44
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    I have supposed the plugin to do both dithering and quantization (since dithering is only useful if the next step is quantization with a compatible bit depth). POW-r seems to be a technology licenced to multiple product like Logic, Samplitude... then I can't verify (it could depends of the actual product). The Dithering alone (20bits) add a noise at around -120dBFS which is huge compared to the quantization noise of the input file : -144dBFS. Then the signal is not enhanced, but degraded. If the plugin does quantize too, the result will also have a -120dBFS noise added. Oct 27 at 15:45
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    I could add that W-r in POW-r is for « word length reduction »… which imply a quantization. But it is true that noise is added by the whole process, not the quantization alone. Oct 27 at 16:19
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    forum.cockos.com/showpost.php?p=196824&postcount=6 seems to correlate POW-r with an old version of dither_psycho from Reaper (the source of which is public). This algorithm dithers the source depending of the 9 last quantization errors. Then this dithering can’t be separated from quantitization. I guess it is the same with POW-r. (I said « an old version », because mine can’t dial the filter order and impose a 9th order). Oct 28 at 15:12

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