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Word clock and MIDI interfaces.

“I have a question regarding a certain feature on one of the MIDI interfaces on the market. I’m in the market to buy one these units but suddenly found myself confused when I saw that the MOTU MTP AV had word clock on it. What is the purpose of this?”

“I believe that I understand W/C and other kinds of time codes fairly well. I guess I’m just lacking practical use of them since my studio is still missing some of the essentials (like a MIDI interface). W/C does not have anything to do with SPP or a certain locate point in time between points A and B, for that matter. So what is its function on MIDI/SMPTE interface?”

Word clock can become important when syncing any digital audio system. It doesn’t really relate to MIDI or SPP per se, however, since many MIDI sequencing systems such as Digital Performer and Logic Audio support MIDI AND audio tracks word clock can be an issue. If you are synchronizing such a system to another recorder or system (audio or video) you want to make sure your audio tracks remain in tight sync as well as your MIDI. The obvious question that comes up here is, “why isn’t SMPTE or MTC from the master device enough to sync the digital audio? Why do I need to fool with word clock?” The answer is that sometimes it is, and you may not. These days many (not all) audio systems are perfectly capable of following SMPTE or MTC data. BUT (there’s always a but, isn’t there?) if your audio hardware has a word clock input you can get more stable sync and take a load off of your computer’s CPU by having the digital audio data clocked externally. When you DON’T do this your computer has to continually calculate and change the sample rate of your digital audio to keep it synchronized with the other equipment. This can put a tremendous load on your computer and degrade the quality of your audio.

When you employ a MIDI interface such as a MOTU MTP/AV it is able to generate a stable word clock that stays resolved to the incoming time code from the master machine. In fact, it is able to assume the master role itself and have everything sync directly to it. Either way this provides more stability for the system, tighter and more consistent synchronization, and less overall aggravation on your part. If you are not synchronizing your computer DAW to external equipment you really don’t need these extra features, though they can always come in handy “just in case.”

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