OatBran wrote on Thu, 20 May 2004 19:16 |
It is the use of the fixed or floating in processing that I am particularly refering to.
I am not sure if PT is fixed or floating. Might need to check on that. Though I am sure Sonic is fixed. I know Steinberg products are all floating and tracks that way as well (unless told to do otherwise). I know Sonic Foundry/Sony products are fixed. I am pretty sure Logic is floating though I am not positive on that one either.
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Pro Tools HD TDM systems are 48 bit fixed point, while Pro Tools LE systems are 32 bit float. You can still have a plugin that calculates at 64 bit float but is fed and returned at 32. Sonic is also 48 bit fixed point. You may notice that Sonic and Pro Tools process on cards tend and are fixed point (not that all hardware has to be fixed point) while programs that do processing done by the CPU are typically floating point.
As a delivery format, 24 and 32 are essentially equal, though 24 is likely to be more widely compatible. Storing at 32 is mostly for CPU processing programs that are storing it as an intermediate file between processing steps. As somebody already alluded, 32 bit float is 24 bits of audio data with an 8 bit mantissa.
All other things being equal, 32 bit float processing will beat 24 bit fixed processing, though it is widely held that 48 bit fixed wil beat 32 float (and I agree). Dr. James A. Moorer wrote a brief paper on the subject if you want to do a search for some reading. 64 bit float gets floating point back in the game. While 64 certainly has a theoretical measurement advantage with the moveable zero, buy the time you reach 48bit fixed, the extra room in 64 float is pretty likely to go unnoticed. Both 48 and 64 are excellent for processing.
Some processors like the Weiss EQ and Studer digital consoles utilise sharc chips using 40 bit floating point precision. Note that some other sharc implimentations process at 32 bit float. 40 bit float probably is indistinguishable from 48 bit fixed or 64 bit float in general practice.
The really important factor is how the designers and programmers make their hardware and software. A crappy 64 bit plugin is going to sound, well, crappy. Excellent 32 bit processing can sound excellent. Just about the only thing that is avoided these days is 24 bit fixed point. With the industry using 24 bit files extensively, you really want a little bit more processing headroom for them (as a general rule you should process at a greater resolution than your source file), and it's so simple to use greater than 24 bit fixed point precision these days. There's no real reason to limit yourself. I also would imagine that 32 bit float processing will eventually give way to 64 bit float in the CPU, or in hardware, 40 float, 48 fixed or 64 float. Now if only we had a 32 bit transmission channel...