DV timecode and drift issue

[davefx]

this is my first post. i've been lurking here for over a year and have learned a lot so far. i have sucessfully created a lot of different types of dvd's from different sources but have recently gotten into more of the DV footage of concerts (these are contracted by the bands themselves and are in no way bootlegged)

several successes of this type of project so far, but the last one i recorded has a major issue that i dont quite understand. the DV tape drifted all over the place.

i use a canon zr80 to record the video, and protools (G4 or G3 depending) to record the audio on quite a few tracks for mixing later. my first few attempts i was amazed that everything stayed in sync the entire time. i didnt imagine it would, but it did. considering the multiple clock sources (camera and computer) i figured it would slowly drift apart, but all except the last attempt stayed in sync for all tapes (typically 3 - 60minute tapes per concert)

after transfering the last three tapes and mixing the audio later in PT, assembling these in FCP4.1 i found the drift was really bad. the audio and video differed by about 10seconds an hour, and the strange thing is that it was NOT a consistant drift. it would drift in and out. this would lead me to beleive that the tape is slowing and speeding.

one example in particular i looked at was a song that started in sync but halfway through the video sped up. the audio on the tape matched the video on the tape, but the PT audio was way behind.

after closely looking at what went wrong i can tell the tapes DID speedup and slow down, but i dont know why it did this this one time only and across all three tapes.

i ended up just aligning each song individually to the audio and comprimising the drift as best i could. its actually not that bad now, but i have never had to do this before.

how does the timecode in DV tapes work? i thought the tapes would playback according to a clock and not at whim like a plain VHS deck.

does anyone know why this happened or how to prevent it in the future? it only has happened once so far; this last time but never had a problem doing this the previous attempts.

[BJ_M]

mini dv has no timecode - you have to use DVCAM, or DVCPRO instead..

saying that -- you should not have that much drift even with mini dv

[crusty]

I have had this happen b4 what I found that in your easy Setup in FCP if you go to your Device Control Presets you will have two options DV Time and LTC. I found that when I set it to LTC the slip in and out stopped even though mini dv has no TC this seemed to stop, not sure why though, anyways worth a try.