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32 bits floating point to 24 bits fixed point
Old 12th February 2007
  #31
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Quote:
Originally Posted by Spartacus View Post
So, thing is, is there any distortion if we stay under a 24 bit dynamic range?
I mean, does for exemple a dance track using only the highest bits and never the ones under around 10 (except maybe for the fade in and fade out) will create any distortion?
There is no such track, unless it consists solely of a really loud sine wave at close to the Nyquist frequency. Otherwise, your sample data will be across the board.
Old 13th February 2007
  #32
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Quote:
Originally Posted by MattGray View Post
In this particular case going from 32bit float to 24bit integar or when going 48bit fixed point to 24bit, I've found that I get the most transparent result by using flat 24bit TPDF dither (no noise shaping). You should really only use 'noise shaped' dither on your final wordlength reduction to 16bits. It's the cummulative affect of doing multiple 'noise shaped' dither processes that can raise the noise floor to an unacceptable audible level.
Matt
Absolutely right - well said :-)
Old 13th February 2007
  #33
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the digidesign le manuals used to say that dithering to 24 bits was not necessary. i don't know what they say now. but in any case, is there a flat 24-bit TPDF dither plugin available to use in ptle? is the standard digidesign dither plugin flat 24-bit TPDF?
Old 13th February 2007
  #34
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Quote:
Originally Posted by dkatz42 View Post
If you were to sample a 1KHz sine wave at 0dBFS and 24/48K, the sample data could range from the maximum possible value all the way down to zero....
yes i see, my mistake was to think "RMS" instead of thinking about "sample"

Quote:
Originally Posted by dkatz42 View Post
In particular, any *single sample* whose amplitude is less than -6dBFS (which is true of the majority) and which has undergone processing will be truncated.
just to be clear : in your exemple, you're talking about a 32 bits float processing or 24 bits fixed? or both?
Old 13th February 2007
  #35
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Quote:
Originally Posted by Spartacus View Post
just to be clear : in your exemple, you're talking about a 32 bits float processing or 24 bits fixed? or both?
Both, I suppose. If you had a DAW that did internal processing at 24 bits fixed, the truncation would happen on every calculation as the processing took place (and there's no conversion to fixed at the end since it's already fixed.) But as far as I know, nobody makes a DAW these days that uses short fixed-point processing.

Processing in wide fixed-point formats has to be carefully crafted so that there is no accidental truncation in the middle of the calculations, which is one of the challenging programming problems in fixed-point engines (and truncation takes place when the word length is reduced back to 24 bits.) Floats make it much easier for the developer.

In the float case, it is likely that individual samples will end up with valid bits below 2^-24, and those bits will be truncated at the point where the sample is converted to fixed point.
Old 13th February 2007
  #36
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Quote:
Originally Posted by feedback View Post
the digidesign le manuals used to say that dithering to 24 bits was not necessary. i don't know what they say now...
They finally came around with HD. Software manuals have been sources of massive amounts of misinformation over the years. Funny how people will complain about what a piece of software sounds like and then trust everything they read about signal processing in the manual.
Old 14th February 2007
  #37
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Quote:
Originally Posted by feedback View Post
the digidesign le manuals used to say that dithering to 24 bits was not necessary. i don't know what they say now. but in any case, is there a flat 24-bit TPDF dither plugin available to use in ptle? is the standard digidesign dither plugin flat 24-bit TPDF?
The only plugins I know that can do this is Waves L1, L2 or Ozone. With waves you obviously don't use the limiter section unless you really need it & just set the dither section to 24bits, Type 1 & None where it refers to noise shaping. This will give you 24bit flat TPDF dither according to Waves. The other way is to use Ozone with all the modules disabled (the dither module works independent of the modules). Use Type 1, None, 24bit, number of toggling bits 1 or 2 if you like. Either of these will give you the result you want.

The POW-r dither module supplied with Pro Tools only goes to 20bits same with the digidesign dither module. So a third party plugin as mentioned is your best option.

Matt
Old 22nd February 2007
  #38
Tui
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Hi all, and my apologies for butting in at this stage of the conversation.

I would like to know, when, during a regular mix (I work with Logic 7), is dithering from 32 to 24 bit necessary, or desirable?

I tend to record audio at 24 bit, and I also use samples, which are mostly 16 bit (I recorded a few sound libraries myself at 24 bit). If I understand correctly, Logic works internally with 32 bit, floating point. Should there be a need for dithering when I finally bounce down to a 24 bit stereo track, which I then send off to be mastered, and dithered down to 16 bit?

Logic's manual only recommends dithering from 24 to 16 bit, and Logic only offers the POW-r #1 - 3 algorithms.

MattGray, do I understand correctly, in that you would recommend dithering even the 32 bit bounced signal?
Old 22nd February 2007
  #39
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Quote:
Originally Posted by Tui View Post
Should there be a need for dithering when I finally bounce down to a 24 bit stereo track, which I then send off to be mastered, and dithered down to 16 bit?
If it's going to be dithered and reduced to 16 bits, there's no benefit to dithering at the 32->24 stage (and as far as I know Logic doesn't give you that option anyhow.)

In any case, the returns are so diminishing that it probably doesn't matter. If my mixes are ever good enough that dithering to 24 bits is the only thing standing between me and a Grammy, I'll be a happy man.
Old 22nd February 2007
  #40
Tui
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Quote:
Originally Posted by dkatz42 View Post
(and as far as I know Logic doesn't give you that option anyhow.)
Actually, it does. Hence my question.
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