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Old 12-12-2011, 12:45 AM
Greg Malcangi Greg Malcangi is offline
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Join Date: Dec 1999
Location: UK
Posts: 491
Default Re: Fixed Point vs. Floating Point

Quote:
Originally Posted by lennieh View Post
The antis say that if you need to use the extra range you get from 32-bit file formats then your gain structure is wrong. End of story. You can't directly present that file to your DA converter, so you have to dither it or apply gain reduction to it, so what's the point, you are just introducing more scope for error.

The pros would say it gives you added flexibility when mixing.

At the end of the day, do some blind listening tests and trust your ears
Quote:
Originally Posted by MADIrouting View Post
I can't say that I understand the 32-bit file process other than it is 24-bit with the 8-bits of headroom when saved.
It's not quite a simple as this.

1. 32bit float is not really the same as 24bit + 8 bit of headroom. That would be 32bit fixed. Basically 32bit float is roughly the same accuracy as 24bit with the additional bits used to define where the decimal point is (exponent).

2. While in theory 64bit float is roughly the same accuracy as 48bit fixed, the situation is a little more complex in the PT TDM world because not all of the signal path ITB is at 48bit, paths to and from inserts are 24bit for example. The 48bit summing mixer is not always 48bit either, there is a 56bit accumulator but depending on the number of channels you're running, the mix maybe invisibly sub-mixed (and reduced to 24bit) if spanning more than 1 TDM DSP chip.

3. The "antis" have a valid point in that floating point summing encourages incorrect gain staging but if you know what you're doing there are some nice workflow advantages to floating point if you're running lots of channels.

4. The "blind test and trust you're ears" mantra is usually good advice but should be taken in context. While you may hear sonic advantages of 32bit float over 48bit for one particular mix (or vice versa), that doesn't mean you have proved a rule that 32bit float is therefore always better than 48bit. There are also some potential disadvantages of floating point summing compared to fixed point summing, the aforementioned gain staging and the application of dither for example.

If I had to make a generalisation, I would say that I wouldn't expect 64bit float to sound worse than 48bit fixed and there are definite theoretical advantages to plugin routing and processing at 64bit compared to the current TDM architecture, depending on how it's implemented within PT and by the plugin manufacturers. I certainly wouldn't be expecting any night and day audible differences, very marginal differences which may only be noticeable in more extreme circumstances.

G
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