Friday, December 14, 2012

Project Movie: Part Seven - Recording the Live Event

I know it's a lot of posts lately about the recent movie project but I want to get it all down while it's still fresh and today's post has some importance for other applications as well.

When the time came to put our show up we had a pretty good input list going and wanted to get every last bit of it recorded so we'd be able to mix down all the live music and actors' performances for the DVD. (If you're just showing up now check out the rest of the Project Movie posts here)

We didn't have an ideal setup but we used what we had. Coming through the Midas Legend 3000 at front of house I had twenty-four instrument inputs, four vocal inputs, a set of choir mics, lavs on the actors and pastor, and a backing track. To get it all in the box I had at my disposal a Presonus StudioLive 24 digital mixing console with Firewire out and a MOTU 896mk3 Firewire audio interface, good for another eight analog ins as well as digital, which comes in later.

For our first full rehearsal I routed the first twenty-four channels of the board to the Presonus via direct outs on the channels. This gave my assistant good control over the gain structure of the recording to prevent overs and make sure nothing came in too cold. The Firewire connection brought it into a MacBook and we recorded in Reaper. The MOTU interface handled the vocals and backing track (we re-recorded it so as not to have to worry about sync as much in the final project.) and brought those inputs into a second MacBook running Reaper.

At the end of the night after two full run throughs we went back to review the tracks. This involved importing the audio from one of the sessions into the other and lining things up. This was easy to accomplish but we found that once we had done it, there was considerable lag on the part of the vocals by the end of a ninety minute pass. Something in the neighborhood of fifty milliseconds. Not wanting to chop things up and line every song up we got to thinking.

What to do? Well, the MOTU has lots of options for bringing in digital audio. S/PDIF, AES/EBU, ADAT, and Toslink. The problem was, the Presonus only has Firewire out. The MOTO can accept an external clock, but the Presonus is again out in the cold. It is possible to bring Firewire audio into the MOTU as well, but not as many tracks as the Presonus had.

The final answer was a simple piece of RCA cable. The Presonus has a S/PDIF out option for sending two selectable tracks of audio. I selected the L/R mix and ran it to the S/PDIF input of the MOTU. A few knob tweaks later I had the MOTU looking to the Presonus for time code and all was well.  Mostly.  The MOTU was actually the better option for clock signal but the Presonus only has digital out.

In the end we got good results. The vocal tracks were lagging less than one millisecond after a ninety minute pass. I have no way to measure the jitter but I'm assuming that since the predominant method of playback will be TV speakers for the final product that only the dog will notice if there is any.

Well Brethren of the Knob and Fader. I hope that info comes in useful some day. As the home recording market continues to grow, ganging multiple interfaces together is a more and more common practice. Just having them slaved into the same DAW on the same machine might not be enough to save you in every situation. Always keep an eye on the clock!

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