Zero Dee Bee, and other myths

[Woodboy]

Been following the "sound quality"/dithering/truncating etc. threads with lots of interest.

Forgive me if I'm asking anyone to repeat themselves, but: When, exactly, is the PT mixer set "in neutral", at unity gain, in such a way that no dithering/truncating math is taking place in the signal path? Fader at 0.0 dB, obviously, but do I set the panpot to zero as well, or to hard left/right? If I listen to one side of a PT output pair, and pan a single channel from left to right, I can see the level drop about 2.5 dB when the panpot's at zero (to compensate for the fact that there are two outputs blasting away with pan at midpoint). So where is unity?

I've seen lotsa dialogue re: dithering in the PT mixer. Anyone have similar info about the audio mixers in top sequencer prg's? In Digital Performer, there's a "Direct Outputs" audio option which resets the DP mixer and presumably removes any math operations from the audio data stream. In Studio Vision Pro, you can set an audio instrument to play through an output pair, or simply to a single output. I assume that if I leave volumes/pans at their default settings, then the DP or SVP signal path should leave my 24 bits of audio untouched? Anybody have an answer on this?

And while I'm on the zero dB kick... Say I have a full-code audio signal - a final mix that's been gain maximized with Finalizer or whatever - coming out of a ProTools output pair directly into an AES/EBU input on my O2R, with everything on both ProTools and O2R set to "unity", i.e. faders at zero, pans hard L/R. Meters show signal coming out of PT right at zero w/o clipping... but on the O2R stereo buss, with all faders at zero, the clip light is on. I have to attenuate the channel input by 3 dB to make the clip indicator go away. What gives? Is there some kinda make-up gain happening at the O2R's panpot stage? Where is the real zero point??

By the way, any word on the data path in ASIO or MAS compared to DAE, when using Performer or Vision? Or even apart from dither/truncating types of issues, does anyone have thoughts on other performance issues (like I dunno... latency, jitter, conversion quality etc.) between, say, Digital Performer running under DAE versus ASIO or MAS with the MOTU audio hardware?

Appreciate any input... thanks people!

[Rich Breen]

Hi Woodboy,

>So where is unity?<
If you're using stereo pairs mode, then faders must be panned hard left or right for unity.

>Is there some kinda make-up gain happening at the O2R's panpot stage? Where is the real zero point<

The 02R behaves differently from ProTools. First of all, the clip lights light early on the 02R. Next, if you're returning a signal to any of the 32 regular faders, unity is with fader at '0' and pans center. If you're returning a digital signal to the stereo return faders then unity is with fader at '0' and L/R pans at their extremes. If you follow these rules and turn dither off, then the 02R will pass bit-for-bit clones of what's coming into it.

Hope that's helpful,
Rich

[Woodboy]

Rich, thanx 4 the help... Coupla follow-up q's for ya:

>If you're returning a signal to any of the O2R's 32 regular faders, unity is with fader at '0' and pans center.<

OK, so that means the signal will be a coupla dB hotter if I move the pans hard L or R, correct? (...since a typical panpot is a coupla dB down in the center of its range...) So I should attenuate the input signal by what, 2 or 3 dB maybe?

Any word on why the O2R's stereo input faders handle levels differently from the regular faders?

Also, exactly how early does the O2R's clip light come on?

And by the way, where are you getting your facts about this stuff? I scoured the O2R manual for mention of this kind of thing, but no luck.

Thanks!

[Rich Breen]

>OK, so that means the signal will be a coupla dB hotter if I move the pans hard L or R, correct? (...since a typical panpot is a coupla dB down in the center of its range...) So I should attenuate the input signal by what, 2 or 3 dB maybe?<

Yea, i think it's exactly 3db, but don't quote me on that...it's been a while since i checked.

>Any word on why the O2R's stereo input faders handle levels differently from the regular faders?<

This is a hotly disputed topic: To my way of thinking it makes perfect sense - if i'm dealing with mono signals, they go to mono faders and i want to be able to pass bit-for-bit copies to busses by setting the fader to '0'. If i'm dealing with stereo signals, they go to stereo faders, and again, the signal out of the fader is bit-for-bit equivalent at '0'. Others don't like this so much, but it works great for me.

>Also, exactly how early does the O2R's clip light come on?<

Not a clue, but roughly a db or so.

>And by the way, where are you getting your facts about this stuff? I scoured the O2R manual for mention of this kind of thing, but no luck.<

I've just spent a lot of time on it...

rich

[Mr. H]

"In Digital Performer, there's a "Direct Outputs" audio option which resets the DP mixer and presumably removes any math operations from the audio data stream..."

Would this "direct output" function be different than the one in Pro Tools?

Sean