EQ IN REVIEW:
Opcode Systems Studio 64 XTC

By Tim Tully

Sync your studio with one box

Opcode’s cross-platform (Mac/Windows) Studio 64XTC is a cost-effective, professional synchronizer for project studios. Although it has a limited MIDI interface, what this box does — as well and as inexpensively as anything else — is provide solid, multiformat, multidevice sync to a variety of digital audio and video devices.

The 64 XTC can serve as a synchronization hub for digital audio workstations (e.g., Digidesign’s Pro Tools, Ensoniq’s PARIS, or any hardware-based audio system that locks to word clock), studios that need to lock to video, MIDI or MIDI/audio sequencers, and digital multitracks like the Alesis ADAT or TASCAM DA-88-family machines.

If you’re working in a MIDI-based studio, you may not feel the need for additional synchronization, even if you score for video. It’s a common project studio practice to use a MIDI interface with a SMPTE input (e.g., Opcode Studio 5 or MOTU’s MTP) to lock a sequencer to a videotape. You just patch an output from the video’s audio track containing the timecode into the interface’s SMPTE input, and it converts the SMPTE signal to MIDI timecode (MTC), sends that to your computer, and locks the software to the tape.

Unfortunately, the SMPTE timecode coming from an audio or videotape transport inevitably drifts over time, however slightly. For MIDI tracks, this is not always a disaster, as the only effect is that some notes will be slightly out of time. (However, this could be a problem with music where very tight timing is important.)

Adding audio capabilities to MIDI complicates the situation. If you use a MIDI/audio sequencer like Studio Vision or the audio versions of Cubase, Cakewalk, or other sequencers, the SMPTE/MTC trick will pretty much lock your audio and MIDI sequence to the videotape by adjusting their playback rates as they continuously resync to SMPTE.

The problem is that changing the playback rate of the audio in order to keep sync will induce jitter, which manifests itself in your audio tracks as distortion, pitch shifting, and even gapping: unacceptable — even for techno. On the other hand, some sequencers may only use "trigger sync," where they start at a specified point and run free from there on, without resynchronizing. In this situation, any variation in the incoming SMPTE means that the digital audio will eventually drift with respect to the MIDI data.

So how do you get a solid time base for synchronization? High-level DAWs like PARIS and Pro Tools lock to another device neither with SMPTE nor MIDI timecode, but a signal called word clock (or a similar, improved system originated by Digidesign called Super Clock). This signal tells the DAW the precise instant at which to fire off each of its 44.1 kHz-per-second or 48 kHz-per-second samples. If the DAW locks to video or any device whose timing drifts, word clock reduces the negative effects of these changes.

To minimize the wow and flutter that can come from a sync master like video, the best answer is a black burst generator. This device is common in video studios, which must lock up a number of video tape decks reliably. It sends a solid, unwavering time-base signal, called "house sync," out to multiple other devices, which then all play and record following the "clock" supplied by the black burst generator. Any professional or semi-pro video deck will have a port that accepts black burst, and be designed so its internal machinery will run on its time and not allow imperfections in the tape or other problems to vary its playback speed. One inexpensive black burst generator, the BSG-50 ($289) from Horita (Horita, Box 3993, Mission Viejo, CA 92690; Tel: 949-489-0240; Web: www.horita.com), can send out six simultaneous black burst streams and a 1-kHz, 0-dB tone for reference.

The 64 XTC does a couple of jobs to integrate all these signals. It converts SMPTE to MTC, but, best of all, it will accept a black burst signal and generate simultaneous word clock and Super Clock signals that will keep your DAW(s) in rock solid sync with any video following the same black burst.

A second sync solution works almost as effectively as using house sync. This involves bringing not only the SMPTE timecode signal from a video deck to the XTC, but the video signal as well. Since the video signal provides the XTC with a time base, the XTC can determine if the SMPTE code is coming in too fast, too slow, or just right. From this information, the XTC can send a word/Super Clock signal that keeps the DAW free of jitter and its resultant ill effects on our audio.

The third, and least reliable, XTC sync method calls for just sending SMPTE timecode from the video deck to the XTC. The XTC will generate a word/Super Clock signal from this, but it provides only minimal protection from any wow and flutter the deck might produce. Frankly, there’s no need to ever use this setup under any normal circumstances, since it’s so easy to send SMPTE as well as video to the XTC. Even most consumer VHS decks have two video outs: it’s trivial to send one video signal to a monitor and another to the XTC. Even if this is impossible for some reason, running the video to an inexpensive splitter box would provide the two outs necessary.

Another XTC feature is its ability not only to lock up multitrack digital tape decks, but also to control these units from a sequencer via MIDI Machine Control (MMC). The XTC works with the ADAT right out of the box, and will also talk to DA-88-family machines with an optional plug-in card. A single cable connects the XTC to an ADAT (or DA-88, once the card is installed), and carries both MIDI Machine Control (MMC) and a sync signal, locking the multitrack to the XTC. After making this connection, you can control the ADAT’s shuttle functions — play, record, fast forward, rewind, stop, and pause — directly from your sequencer, and be sure the sequencer and ADAT are all in nearly perfect sync.

In this setup, you can digitally transfer audio tracks from the multitrack to the DAW, edit, process or otherwise alter them, then transfer them back again to the spot from which they came. The lock-up between the devices is tight enough that the variance should be no more than a few samples either way. An ADAT 9-pin sync option, designed to provide sample-accurate ADAT sync, is in the works.

The 64 XTC’s MIDI implementation is emblematic of the way digital audio has been gaining on MIDI in the project studio recently. Opcode has given the XTC only two MIDI ins and four discrete MIDI outs, rather than the eight ins and eight outs that have become something of a de facto standard in pro-level MIDI sync boxes. (The unit actually has six MIDI out jacks, but two of them only send duplicates of the data coming from two other jacks.)

If you have more than four multitimbral MIDI instruments, or two multi- and four monotimbral, you’ll have to use the MIDI Thru ports of your instruments or network the 64 XTC to a more well-endowed MIDI interface like Opcode’s Studio 128X, an 8-in, 8-out unit. But if you’re not so MIDI-heavy, you can maximize the XTC’s MIDI ports with a little planning, particularly if your studio uses any monotimbral instruments — those that receive MIDI data on only one channel, such as the classic Oberheim Matrix 1000 or the growing Yamaha VL series. If you set these to different channels on the same port, each will receive MIDI data intended for the other, but ignore it as being on the wrong channel.

The Studio 64 XTC is well thought-out and functional. It can be valuable as a source of synchronization in many intermedia situations, and has a breakthrough price. If you need to lock digital audio, MIDI or video together, it’s a good choice. Combined with an inexpensive black burst generator, it’s hard to beat.

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