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  #1  
Old 05-24-2004, 09:20 AM
Pricey2 Pricey2 is offline
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Default Confusion about HD\'s 48-bit mixer

This is a newbie question. I've read that HD's mixer is 48 bits throughout, instead of truncating the signal to 24 bits between DSP chips. However, someone told me that the output of TDM plug-ins is still truncated to 24 bits. Is this true? Is it also true of RTAS plug-ins?
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  #2  
Old 05-24-2004, 10:36 AM
Dan Pinder Dan Pinder is offline
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Default Re: Confusion about HD\'s 48-bit mixer

http://www.digidesign.com/digizine/a...ay04/techtalk/

That should answer a lot of questions.

All TDM plug-ins take 24 bits in, process higher, and output 24 bits. Whether or not the plug-in dithers is up to the developer. Not positive about RTAS.

Nothing is truncated (apart from plug-in outputs) when you use the dithered mixers (stereo or surround).
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Old 05-24-2004, 11:25 AM
Pricey2 Pricey2 is offline
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Default Re: Confusion about HD\'s 48-bit mixer

Hmmmm. Digidesign's white paper only talks aboout the summing bus. They're not very forthcoming about the fact that plug-in output is limited to 24 bits.
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Old 05-24-2004, 12:46 PM
Pricey2 Pricey2 is offline
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Default Re: Confusion about HD\'s 48-bit mixer

Another question. In a TDM system, are RTAS plug-ins also truncated to 24 bits at the output?
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  #5  
Old 05-24-2004, 02:54 PM
Extreme Mixing Extreme Mixing is offline
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Default Re: Confusion about HD\'s 48-bit mixer

What is it in your sound, that is 140 db down, well beyond the capability of your converters to reproduce, that you feel you would be missing by processing your plugs at 24 bit? Are you sure that's going to spoil the party?

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  #6  
Old 05-24-2004, 03:11 PM
Pricey2 Pricey2 is offline
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Default Re: Confusion about HD\'s 48-bit mixer

It's the cumulative effect that I'm worried about. You're losing about 1 bit of resolution for every plug-in the signal passes through.
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Old 05-24-2004, 03:24 PM
poppy poppy is offline
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Default Re: Confusion about HD\'s 48-bit mixer

Sorry if this sounds dismissive but If it sounds good it is good!!
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Old 05-24-2004, 06:05 PM
Chief Technician Chief Technician is offline
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Default Re: Confusion about HD\'s 48-bit mixer

The 48-bit mixer in HD is the same 48-bit mixer in MIX.

The plugins use double-precision processing. They divide the 48-bit data into two (2) 24-bit words.

What Digi isn't confirming (but my math confirms) is that with 192 voices, all playing the exact same program material (i.e. 1kHz tone on 192 tracks), you have .5 bits of the 48 bits in the mix bus left.

Take a 1kHz sinewave (regardless of sample rate) at 24 bits. Raise its level +12dB above unity (as you can in v6.4). Now, place that same sinewave on another track, and raise its level +12dB above unity. The whitepaper claims that when you sum two (2) tracks with coherent program material, you get a +6dB gain. Using the well accepted rounding that 6dB=1 bit, the above configuration yields a 27-bit signal. Four tracks of the same material yields 28-bits, eight yields 29-bits, sixteen yields 30-bits, thirty-two yields 31-bits, sixty-four yields 32-bits, 128 yields 33-bits. You would have to have 256 tracks to get to bit 34, and since you can only have 192 tracks voicing at once, you would still be in the 33rd bit's range. Now, there are 16 noise floor bits as they are called. 16+33=49. Since 0 is a bit, we'll subtract one from 49 and get 48-bits!

If Digidesign releases a 257+ voice system, their mix bus will have been recoded. Of course, they could correct me if I'm wrong, but they haven't (yet).
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  #9  
Old 05-26-2004, 06:38 AM
Pricey2 Pricey2 is offline
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Default Re: Confusion about HD\'s 48-bit mixer

Thanks for the info, but it has nothing to do with my original question. I want to know if the plug-in bus is still 24-bit. Can I get confirmation on this from a Digi tech? Are there any plans for a 48-bit plug-in bus?

I may be working at an HD-equipped studio in the near future, and I want to know exactly how the system operates.
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Old 05-26-2004, 12:56 PM
PastaViking II PastaViking II is offline
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Default Re: Confusion about HD\'s 48-bit mixer

Pricey2:

I think the first reply you got from Dan answers your first question (yes!). The second question will most likely not get answered by Digi....

pv
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