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Microphone Month 3

Trouble with playing back SMPTE data from compressed formats

We’ve had a few people recently ask questions similar to this one.

“I have been using custom made audio CD’s in live gigs. They have audio on one channel and SMPTE data on another to synchronize my sequencer to the CD. Recently I decided to port these over to my MP3 player because it has no moving parts and is easier to deal with, but the sequencer no longer syncs to the SMPTE Time Code. What’s wrong?”

MP3 and some other popular audio playback formats employ data compression. The premise is that with a sophisticated encoding and decoding mechanism a substantial amount of the original 44.1 k, 16-bit data can be removed without significantly impacting the overall audio quality of the material. The mini-disc was an early format that tried audio data compression, and while the first generation machines didn’t sound that good, the algorithms have been revised several times and are now pretty darned convincing. Many people feel MP3 is still quite a ways away from this kind of quality. The problem you are encountering with the SMPTE Time Code is that, unlike audio, which is subjective, SMPTE must be exactly reproduced in order to work. You simply can’t drop a few chunks of data here and there and get away with it. The reconstructed audio may “sound” like SMPTE Time Code to our ears, but we’re talking about data that has to be exact. No doubt your data is garbled on the MP3 device to an extent that the synchronizer can no longer read the time code. You are probably going to have to return to using the CD player.

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