Using a Rosetta w/ a MOTU box...

I got this question in my email this morning from a Bill:

I just ordered a rosetta 800 and was curious as to how to hook it up to the MOTU. For now, I just want to use as a front-end (not using with the firwire card). Are there configurations that capitalize on the conversion that are better than others? How exactly do I hook it all up? Do I input my external pres directly into the rosetta, or do I just connect them to the MOTU as always and let the rosetta via optical and wordclock do the rest? Also, I use the Mackie Big Knob for monitoring .. how do I monitor the rosetta DA? Does it still come out of the MOTU main outs or would go out from the rosetta directly into the Big Knob?

I replied, but the mail bounced, and I thought the answer might interest other people, so in the interests of posterity, here ’tis:

It’s pretty easy. You hook the Rosetta to the MOTU via the optical cables (in and out.) I strongly suggest clocking the MOTU from the Rosetta, rather than the other way around, as the clock in the Rosetta is much better than the one in the MOTU. You _can_ clock the MOTU from the ADAT input, but it is generally accepted that the better way to go is with the Wordclock input.

So get yourself a BNC cable, as well, as you’ll need that for the wordclock. Just run the WC out of the Rosetta to the WC in of the MOTU, and set the MOTU control panel to clock off the Rosetta. Set the Rosetta to whatever sample rate you normally work at, and you’re disco.

As for the other bit, that’s really a matter of taste. As soon as I hooked up my Rosetta, I sold my MOTU and used the money to buy a Lynx AES16 card. The MOTU is a nice box, and I made several albums with mine that I’m happy with, but it just isn’t in the same league as the Rosetta, and I could see that I wasn’t going to use it. Also, with the Lynx AES16, you’re going to be able to get down to 1ms or less of latency; the lowest I ever got my 896 to run without error was about 6ms. I have the Eventide Eclipse hooked to the AES16 as a send effect, and since there isn’t any A/D/A conversion, it is even lower latency, 0.45ms according to the “External Effect” doohicky in Nuendo, which is basically instantaneous, as far as we humans are concerned.

But, if that isn’t in the cards, I’d hook all your pres to the Rosetta to take advantage of its far better A/D convertors, and monitor from the output of the Rosetta, and just use the MOTU as a Lightpipe to Firewire convertor, basically. To do this, you’d set the stereo output of your DAW to be Lightpipe 1/2. Of course, you need a DB25->XLR cable to get the outputs of the Rosetta, but otherwise you’re good.

I really frown on the Mackie Big Knob, and it is definitely going to be the weak link in your chain at this point. It uses op-amps in the signal chain, and colors the sound. At the VERY LEAST, switch to a Presonus Central Station, which just has relays inside, and has no op amps in the signal chain for the mains. The Big Knob will kind of take away the benefits you’re getting from having a Rosetta in the first place.