There's no need for an audio cue.
Just have all cameras roll and then use a digital camera to fire it's flash.
Make sure all the cameras can see the flash.
Use this as your sync point.

Mike

Mike, that's a good idea, but I would need an audio signal simultaneous with the flash so I can sync the hall recording with the video
.

If you have good sound on one of the close cameras, you sync the cameras with the flash, then sync the good soundboard audio with the closest camera audio.

Dave T2

The reason I made the suggestion I did is that sound has a definite speed and a camera further away will be out of (audio) sync with a camera much closer to the action.

Mike

hmm.. i found the quick and dirty way is to use 3 finger snaps mind u the cameras have to be close enough to pik up the audio, however in post, having those 3 reference points (as opposed to one) allows for a tighter sync.

I thn use the timecode on teh cameras and log th emillisecond differences, this way if i inadvertantly lose sync, i just find the timecode again

>>The reason I made the suggestion I did is that sound has a definite speed and a camera further away will be out of (audio) sync with a camera much closer to the action.<<

Right, that's why I want a simultaneous audio/visual signal, so I sync each camera's video directly to the soundboad audio and ignore the camera audio (the first time I tried, this, I just synced all the audio tracks to the soundboard audio, but then I had to slide the video of the rear hall camera 4 frames or so to match up sync). I could use a traditional clapboard, but I figure that since an LED is on or off, so it would be easier to find the exact sync point.

JD - great idea, but might be tricky to see the sync point with the different camera angles.

Sound travels 1.131 feet per millisecond at 72F (it varies depending on air temperature and, to a lsser degree, humidity and altitude.) Each frame of video in NTSC-land is 33.36 milliseconds. In 33.36 ms sound travels 37.75 feet, so just slide the rear hall camera 1 frame for each 37.75 feet it was from the stage. It's not going to be exact since we're dealing in 33ms increments, so if you need to, error on the side of the visual leading the audio, humans are used to seeing something before they hear it.

In PAL/Metric-land, sound travels .344 meters/millisecond. A PAL frame is 40 ms and sound travels 13.8 meters per frame, slide the camera 1 frame for each 13.8 meters it is from the sound source.

John

Ummmm.... have you thought of just clapping your hands? Worked fine for film. Of course the slate board (with hinged clapper) was better. This isn't a problem needing a technical solution.

Thanks for all the replies, but ....

The soundboad mic and 4 cameras are all in different positions in the concert hall.

The logical way to sync the soundboard audio and the 4 video streams is to shoot a clapboard at the front of the stage before and after each concert segment, and line up the clapper video with the corresponding spike on the soundboard audio, which is what I plan to do.

What I am looking for is a gizmo that might give a video/audio indicator that's easier to read than a traditional clapboard.

>>so just slide the rear hall camera 1 frame for each 37.75 feet it was from the stage.<<

John - thanks for the rule of thumb. When I fixed the last one, I was amazed at how sensitive we are to late sync....

Doorbell?

Quite a few wireless on the market, many with flashing lights and tone, and all work with one pushbutton & however many *bells* as you want to buy.

I often use a dog training clicker. Way up in the upper register, it works wonderfully at leaving a clean spike. Good for about 50 feet, any further and you'll need a reinforcement system of some kind.

Hey Nolonemo -
Here's a relatively inexpensive way to proceed.
You buy an inexpensive digital clock with large numbers for each camera (we got some nifty ones at Radio Shack for under 10 bucks each).
Prior to the shoot you sync them all together - "One, Two, Three - CLICK" - they should be within a second of each other.
Now any camera can start or stop at anytime.
(If the show runs more than an hour, you will LOVE this method).

Once any camera is started, zoom out all the way, and take a shot of the digital camera "face-time".

Back at the editing room:
Offset your time-line to match the camera with the earliest time.
From there on out, it's a simple matter to sync your other cameras to the timeline. Just slide the time indicated on the clock face to the time on the timeline. You'll be within frames of dead sync, if not exactly "on".
v
It's a simple manner to line up the times to

Symphony - ask the percussion section if they have a slapstick. You hear this
used in the holiday classic "Sleigh Ride".

Starter Pistol - actually kinda dangerous. Our high school uses the electronic
machines. But fun to use.

Since you won't be using the audio from the furthest camera, video synch is all that matters.

Find a movement which has an exact point, e.g. a violin bow reaching the end of a stroke before changing direction, a conductor's hand reaching its highest point - anything where you can definitely define a visual frame, mark that on each track and line 'em up.

That's what was good about a clapper - it gave you sound AND vision synch points.

Next time, as suggested - a camera flash from near the orchestra which all cams can see.

Wow, thanks for all the comments.

Since I need both sound and vision synch points, I'm going to use a trad clapper slate. But I'm also going to stop by Radio Shack and pick up the parts to make a gizmo that will fire a high intensity LED and piezo beep when you push the button, just to see how that works - like the camera flash with an audio spike.

ummm... yeah, Serena's hit the nail on the head.... or palm on the palm.

Hold your hands high over your head so all cameras can see it and clap, once, loudly. If you want to get fancy, shout the scene and take number before you clap.

You can mess around with Radio Shack parts if you really want to... but I imagine you'll already have your hands with you on the shoot, and hey, no assembly required.

1) Unless you've got genlocked cameras you cannot achieve perfect sync. There'll be an error of max +/- 0.5 frames. In most circumstances that doesn't matter but watch out for it during long dissolves between two camera angles of the same fast moving subject like drummers and dancers.

2) If you're going to use waveform cues from music etc, if at all possible turn Off all cameras AGC, it can mush waveforms so much it becomes very hard to 'see' things.

3) If you're planning on using audio from more than one device for say Room you REALLY need to watch sync, a one field error can be a huge offset when mixing sound from the same source recorded at different points in a hall. I've tried doing this thinking I'd save on using a couple of extra mics and the results were pretty mixed up. Next time I'll run the desk feed into two channels and two ambient mics into another two tracks on the one recorder.

Bob.

>>Hold your hands high over your head so all cameras can see it and clap, once, loudly. If you want to get fancy, shout the scene and take number before you clap.<<

I figure if I stand up in front of the stage and clap my hands above my head, people will think I'm some kind of wierdo, but if I clap a slate board, they'll all think "Oh, movies." :-) I should probably forget about flashing lights and beeps -- but again, this isn't Boston, it's L.A.

If you're going to build something, why not build it into the clapboard? Use a microswitch to trigger it when the clapper hits the board.

A good sharp hand clap does the trick in many cases.

nolonemo - responses seem to be all over the map, and I think perhaps that's because it's not clear what is your objective.

First of all, is your intended output going to be two channel audio or multi-channel? I am guessing that you are trying to create a multichannel soundtrack (5.1?) with "surround sound", where you capture audio in a back hall and put that into the rear channels. I'm guessing, because you didn't seem to say so explicitly.

That said, are you trying to get the audio in perfect sync on all cameras? If yes, why? Someone sitting in an auditorium won't hear front and back sounds in sync, because they aren't. Reverb (or delay) in the rear channels is the real deal. In such a case, it seems like sync on the video (like the camera flash suggestion) is all you'd need. If you want to slide the back-channel audio for some effect you can do so.