Slaving Audio to SMPTE & drifting audio

Whenever slaving audio in the computer to an external source such as SMPTE, you must have Word Clock a (Time Base) as well as address (SMPTE or MTC). The Word Clock tells the audio in the computer exactly how fast to go. Without Word Clock, the rate or speed of the audio in the computer will never match the speed of the audio outside of the computer. The symptom would be that your audio would drift over a period of time.

The solution is to use an MTPAV or a device such as a BRC. The MTPAV will convert the incoming LTC (or SMPTE) and generate MTC (the Address) for the computer as well generate Word Clock (the Time base) for your Audio Hardware. If you have Audio Hardware with a Word Clock input (to connect the Word Clock to) such as MOTU Audio Hardware, then the Word Clock will keep the audio in the computer running at the same rate as your external audio for phase accurate sync.

Note: Some software programs offer a feature that may be called “Sync Audio to Time Code”. While this feature may work for short sound files it is not the proper solution. This method works be actually pushing or pulling the audio according to the incoming address since it has no Word Clock to reference to. This method could also cause artifacts in audio playback.

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