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Syncing digital audio to analog tape decks

Another sync question: “I have a TSR-8 that I would like to synchronize with a new computer digital audio system I am putting together. I currently sync Cakewalk (MIDI only) to it, but I have heard that the sync from an analog deck isn’t tight enough for digital audio and that I need to use a time code interface with word clock, which will drive the digital audio sequencer with more accuracy. I’ve also been told that this can cause excessive lock up times as opposed to just syncing MIDI. Is there a better way?”

Whew! We’d have to go through a small course in synchronization to answer this one question fully, which we obviously don’t have space for. Here are a few points that should help. Then you should definitely talk to your Sweetwater Sales Engineer for more in depth advice.

Yes, syncing audio tracks to anything else is much more involved than just syncing MIDI. We’ve had quite a few tech tips over the years touch on various aspects of this and you may want to search the inSync archives for those. You can try to use a SMPTE to MTC (MIDI Time Code) converter as is built in to many MIDIinterfaces for this. The problem is that the computer audio has no clock reference so it will just play at whatever speed the computer tells it to. The only way to get digital audio to play at different speeds is to change the sample rate. This means that either your computer has to do sample rate conversion on the fly (very CPU intensive) or just let the audio play at normal speed, which will cause it to drift out of sync with the TSR-8 over time. If you’re working with short enough pieces (like commercials) this may not even become noticeable, but for most people the drift is too great to wing it like this. Some programs allow a workaround by letting each audio region sync to the current time code. That way you can cut your audio into enough discrete pieces that it will appear to be playing in sync.

The only professional solution, however, is to generate accurate word clock that is resolved to the time code coming off of the analog machine. This word clock can then be used to clock the audio from the computer, which will keep it in sync. The sample rate, and thus the speed and pitch of the audio will change in real time based upon what is happening with the analog machine. Of course being able to do this is predicated not only on having a SMPTE reader that will generate word clock, but also on having an audio interface in the computer that can accept it.

As for lock up times, if everything is working properly they shouldn’t be excessive. Best case for audio is that it still may take longer than MIDI only, but lock up times of 20 seconds means something is wrong. Lock up times are affected by all the components in the system from the time code reader to the digital audio hardware to the software to the computer itself. Keep in mind that there may be qualitative differences between certain equipment. All SMPTE to MTC/Word Clock converters are not created equal for example.

Also, as an aside, Tascam makes a hardware interface that will allow you to control your TSR-8 via MIDI machine control. It will not have any affect on the sync performance of your system, but may make life a bit easier since you will no doubt find yourself working in the computer more now.

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