Thread: syncing audio w/ video word clock/video blackburst help

hey guys...

i recently purchased a lucid ssg 192 master word clock generator for syncing a few of my ad/da convertors together and had a question about it regarding film audio....

it says it supports video blackburst...? im going to be doing audio for some live concerts that a friend will be recording with his video camera and for a few other projects... does anyone know how i should set this up? i have sonar 4 studio and i will upgrade to professional so i can get the video thumbnail... but what about the word clock? should i set it to video blackburst ntsc for when im recording audio for video? what will it do?

Also, do i need SMPTE time code as well?? im so confused on this whole topic.... if anyone could refer some good articles thatd help a ton.



thanks

dan

Originally Posted by photoresistor

wow thanks so much for your reply! This stuff gets confusing FAST.

Well im disappointed in the GL2 not having the ability to sync... this is not a cheap camcorder either. do you know off hand of digital camcorders that do have the abliity to sync? are they found in only very expensive units?

And sorry for my ignorance, but what is NLE?

And I have no idea if this might work, but the lucid clock generator also has a video input and it can distribute that as sync... would this work say having a video out of the camcorder going to the lucid generator? would that keep the audio and video in sync? (as a word clock and not timecode... then i could use a clapper or something to get them together)

Thanks again for your reply! If you could elaborate on some of this other stuff (drop frame, chasing audio to vid) thatd be great as well.

dan

The technology that enables a camera to synch to other equipment is called "genlock" and is a feature of professional broadcast equipment. It's main use is to insure multiple cameras and other video equipment such as titlers are scanning their frames exactly in synch with each other so you can switch on the fly without jumps in the picture. It's actually not needed for double-system sound on DV which is what you're talking about. If video is recorded in DV and sound is recorded digitally, the clocks in the two recorders will keep close enough to each other to maintain synch between audio and video over a reasonable period of time without doing anything special.

"Drop Frame" refers to the way SMPTE timecode is recorded in video. Video is nominally 30 frames per second but with the advent of colour some room had to be made for colour information and so the frames were "squished" a tad. This meant that there are now 29.97 frames per second, not exactly 30. If the timecode counts minutes, seconds, and frames at 30 frames per second, the numbers displayed will drift slightly away from actual "clock on the wall" program time over time. At the end of 1000 seconds, our timecode counter would say we've shown 3000 frames but in fact we've only shown 2997. So that's fixed by skipping a couple of frame numbers every so often - there's no INFORMATION dropped, it's just the COUNTER goes "...27, 28, 29, 2, 3, 4... instead of "...27, 28, 29, 0, 1, 2..." once a minute except on the 10's. That way the frame count and the running time stay close together over the duration of a show.

NLE stands for Non-Linear Editing and is the hardware/software combination that is used for post production. Avid, Final Cut Pro, Vegas, and Premiere are some of the leaders. Video is captured from the camera as AVI clips on disk, Audio as WAV files. You can line cut, trim, arrange etc on a timeline on the screen. Each clip or event can be placed independently so in your case the video track would be placed on the screen, your audio would also be placed on another track, and the two lined up - a simple clapper lets you identify the exact frame where the two sticks come together and you hear the clack in the sound, often actually can see the peak in the waveform. Since the software lets you slide them back and forth in time independently, it's a no-brainer to line them up.

Another feature of some NLE software, Sony Vegas for example, is that it can change the length of an audio clip without changing the pitch. So lets say you line up your clapper at the start of the video for a single shot that lasts 10 minutes (very rare for one shot to last that long but for discussion lets say it does). When you look at the last few seconds the synch has drifted by a noticable amount. The editor simply grabs the end of the sound event with his mouse and drags it over to line up with the end of the video clip. Since the head is locked, the two will be of identical length and maintain synch thru the whole shot.

Another trick is to use the camera's on-camera mike to record a scratch track. It'll sound lousy but it can be used to line up the good audio track from your recorder during editing and then thrown away.

By the way, try to set your audio recorder to use the standard DV audio sample rate of 16 bit/48kHz instead of the CD norm of 44.1 kHz. It'll make post go much smoother.

In short, don't worry too much about sending timecode between camera and recorder. As long as you record digitally in both and have a record of what part of the sound recording goes with what part of the video recording, you're not going to have major issues in post.

Hope this helps

Steve