Annoying DV capture with 48.009khz audio???

[Rafael Amador]

David,
Could that be related with lock-no lock audio DVCam/MiniDV?
Do that give you any problem when editing? Audio have to be rendered or so?
rafael

[David Roth weiss]

[rafalaos] “Audio have to be rendered or so?”

Yep, the audio has to be rendered. Its a small pain, but just should not be happening.

[David Roth weiss]

[rafalaos] “lock-no lock audio DVCam/MiniDV”

What’s that???

[Rafael Amador]

Sorry i can not help you much. The only thing i can think about is the quetion of the not-locked audio in the MiniDv. However I shoot with a DVCam but almost always in DV mode and, although the audio its suposed to be non-standard, I never had this problem with my DSR-11.
Have you tried to download with another device?
rafael

[Rafael Amador]

The only recogniced advantage of the DVCam over the MiniDV is that in DVCam the audio is “locked” , i didn’t read much about but this but is suposed that in the “non-locked” audio could be a subtle fluctuation in the data rate or so. Any way SONY in theyr brochures after talk a lot about this advantage recognice that this posible variation is imposible to detect by the human hearing. So in fact that advantage is not much usefull. This is why I shoot mainly in MiniDV mode instead of DVCam and I’ve never had any issue with the audio
Rafael.

[Blub06]

As far as I understand, the advantage of DVCam over shooting DV is that the tape moves faster thought the recording process which allows the legendary Sony error detection and error correction process to work it magic in a much better way. As I understand, the frame is recorded to a memory buffer then sent to the tape to be recorded, the deck then checks to see if it was recorded properly then dumps the buffer. If the frame was not recorded properly it then tries to record it again but on an earlier or later part of the tape. Once again the electronics checks to see if the frame was recorded properly. Faster tape means lots more room to store that frame if things are not all well with the tape or camera.

As far as the 48k issue, I remember back in FCP1.25 days this happened to me. I think I was able to hear the audio when playing back without rendering. I think this only happened on clips that were over 7 minutes in length.

Just for a joke, check the menu of the deck and see if its in 32k default mode. I also wonder if the tapes were recorded with a Sony camera?

Chris

[Bret Williams]

Shouldn’t have to render audio in any case. FCP can make the conversion in real time. 10, 20 or more tracks. Just depends on how many real time audio tracks you have chosen in prefs.

DVCam locked audio has something to do with the audio samples being locked to particular frames. As I understand it really comes into play with linear editing, so that when a camera does shoot out of exact 48, it won’t affect you when editing linear. Supposedly this doesn’t make much of a diff in non-linear, where you’re capturing chunks that can then be analyzed by the system.

FCP does analyze your clip when digitized or imported. When you place a clip in a bin, FCP checks the number of audio samples, and the number of frames and does some basic math to determine the audio rate so that FCP doesn’t play the audio back at the wrong rate. If FCP were to play your audio back at perfect 48 when it’s not, then the audio would slowly drift out of sync, noticeable after a few minutes. Not noticeable on shorter clips.

There used to be a checkbox in user prefs that made this checking an option, but there was no reason to leave it turned off. I guess they got a lot of “out of sync” complaints from people with it turned off.

At the time, the notorious cameras were the canon xl1 and gl1. I don’t think anything has changed. They still have audio and head alignment issues 8 years later.

But anyway, the 48.009 khz thing is fairly normal. It’s 99% of the time simply the way the camera recorded it. It shouldn’t require rendering. Of course you’ll do a mix down before output as always.

[David Roth weiss]

THNX Bret!!! Now at least I know what its all about and I won’t be concerned.

[Rennie Klymyk]

I’ve had this audio issue before too but it’s been a while.

I just wanted to add some thought about DV vs DVCAM. DVCAM moves the tape 33% faster past the heads. The head drum doesn’t go any faster and it’s angle doesn’t change but we get 15micron pitch as opposed to a 10 micron pitch on the same tape. When the helical scanning heads make a swipe on the tape a skewed retangular shape is written to the tape. If you viewed it vertically you would see a series of skewed retangles one above the other in which the right side was higher than the left side. Before one skewed square ends on the bottom left of the pattern the next swipe of the heads begins on the right so there is no space on the tape between these patterns perpendicularly . With dv footage this overlap is miniscule but on dvcam these squares of data are longer in shape because the tape is moving faster as the drum spins and the heads lay down the data. This results in more overlap of these patterns so as the play heads later read this data it is reading the new skewed square (head swipe) at the same time it is finishing the previous one. This is why locked audio is possible on dvcam and why dvcpro 25 (18 micron pitch) decks can scrub video and audio faster than dvcam. When mini dv came out we got betacam sp quality (1/2″ tape) on a tiny 1/4″ tape that recorded an hour. Tolerances were tight.