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Recording Multi-cam Audio

A Creative Cow Feature Article


Recording multi-cam audio
Brandt Sleeper Brandt Sleeper
Ingram, Texas USA
©2008 Brandt Sleeper and CreativeCOW.net. All rights reserved.

Article Focus:
Editing multi-cam audio is a hot NLE feature. Maybe you're ready to shoot the video -- but are you ready to capture multiple audio sources for your multi-cam shoot? Brandt Sleeper offers tips for multi-cam audio shoots, from ENG to the front row.


Over the years, the thought of a multi-camera ENG/EFP shoot was considered a luxury indulged only when an “A” list correspondent graced the scene to do a high-impact interview. The restriction was of a pecuniary nature because it entailed two crews, which was an expense rarely deemed requisite.

Instead, a producer typically does the interview off-camera and the interviewee is prompted to answer the question(s) in a manner that would imply the query. This technique was and still is quite effective because when the subject does a good job of including the question in the answer the piece can be cut together with B-roll and still maintain continuity.

The alternate method is to have a lesser-known talent ask the questions with an over-the-shoulder two-shot focusing on the interviewee. Then, after the interview, the reverse angle shot would be staged and the editor would cut to a staged reaction shot of the talent nodding in agreement or perhaps even asking the question to the invisible and typically absent subject.

These days; however, the possibility of a shoot involving two or more cameras is quite common. Reality TV is a classic example where each camera follows a given subject throughout the program while other cameras do the same with their subject(s).

It has become cost effective because most of this kind of shooting involves DV or HDV cameras. Due to the relatively minimal expense of these formats, it is quite feasible to own two or even three DV cameras for less than the cost of a single high-end tripod and fluid-head.

In true “guerrilla” style video, each subject would have a wireless lavaliere or shotgun feed sent directly to the camera. In more production-oriented shoots, a sole audio mixer can feed multiple cameras; possibly one channel with the complete program content for reference while the other channel contains discrete audio relative to that camera’s visual.

I personally do almost all of my shoots with two cameras because I can cut seamlessly between the two shots: one maintains the WS or MS while the other captures the MS or CU respectively. Additional cameras might capture establishing shots or perhaps cutaways.

For documentary shooting this method ensures cutting ease without sacrificing the true documentary approach. On shoots where the topic is emotional or the event cannot be recreated, use of two or more cameras can effectively multiply the footage allowing for more interesting edits without cutting to B-roll. In post the only issue then becomes sync.

The technique for multi-camera sync is no mystery but may seem elusive as industry secrets are often heavily guarded; so, I have decoded the cipher and herewith offer it for your benefit.

There are several mixers on the market that offer multiple outputs for cameras. With these, you simply feed the various outputs to the appropriate camera. If your mixer does not offer this feature, you can introduce an XLR splitter to each output, thus supplying two or more feeds for the additional camera(s).

With a hard-wire setup, you usually have a return feed from the camera for confidence monitoring of at least one of the cameras. If you need to have independence between the cameras, send the audio feed via wireless.

Always have the camera operators monitor their camera to ensure quality audio and alert you to possible RF problems. Sync used to be a big problem during the edit prior to the days of non-linear editing; however, in this day and age it is a simple matter to visually line up the audio wave files of each camera in post.

A quick audition of the two audio sources will let you know if you have to nudge the wave to the right or left a frame or two. Once this is done, the image will be in sync between the various sources.

There are more accurate methods if you have timecode capability on the cameras. These are generally employed during the shoot itself.

First make certain that both cameras are set at the same frame rate (DF or NDF). Then the standard procedure is to take the TC-out of the Master camera which is set in REC run for TC generation.

The output is then feed into the TC-in of the Slave camera on which the timecode is set to FREE run. The Slave TC will run continuously until it receives the TC from the Master as it begins to record; at that time the Slave TC will jump to the same timecode as the Master.

Always count the TC off verbally to the other camera operator to ensure that the two are in sync. After this you should be safe.

In the event that the TC has to be detached, the cameras will stay in JAM sync as long as they remain in record. Periodically you will need to re-jam the two cameras (typically every 4-6 hours).

Another method is to send the TC to the Slave camera using wireless. This is more accurate than the JAM sync method as the timecode is continuously sent from the Master. During post, you capture the two tapes using the same timecode in and out numbers. Then simply line up the two files and they will be in sync.

Now, lets say you have a somewhat more demanding situation that requires more than two DV/HDV cameras without real time-code that you wish to sync in post-production. In this example we’ll assume a multi-camera shoot of a concert, theater or staged event that involves a house PA of some type. Here is a simple and inexpensive method of sync via audio that just requires a little planning. In a nutshell you will need permission to shoot, a multi-receiver wireless audio system, and knowledge of the frequencies you may use.

The idea is that you can send audio via one transmitter to as many receivers as you wish on the same frequency. With this in place you can send the same program content to each camera.

It is important to realize that when using wireless transmission the signal is companded. This means that the signal is compressed at the transmitter to fit into a finite bandwidth and then expanded at the receiver to regain the full spectrum content. Unfortunately, this does compromise the audio somewhat and while it is probably not an issue with dialog, with music this may be less than desirable. The fix is to get good audio to at least one camera; so… here is the plan.

Prior to the shoot, contact the event Director to get permission to use a wireless audio system. This is primarily to learn what channel(s) you should use to avoid RF conflicts which is extremely important because most musicians/actors/conventions are also using wireless systems and you cannot interfere with their frequencies. Moreover, you don’t want them on your frequency.

If there are additional crews (e.g. television) also get permission/frequencies from them or they will shut you down!

Next, you will need to rent a wireless system that includes one transmitter and as many receivers as you need on the same frequency. Comtek has a popular system that includes one transmitter and 4 receivers. Give the frequency information supplied by the Director to the rental house so that they deliver a system with a usable frequency or deliver a frequency agile system. If you get an agile system make sure you understand how to set the frequency, as it may have to be changed on-site.

The system should come with an adapter that will convert from XLR or ¼” phone plug to the transmitter input. Specify this when renting. Keep in mind that most consoles or PA systems output at +4 line level so the transmitter may require impedance conversion from line to microphone-level or a pad to reduce the output. Again, the rental house should have this already available and in place. You should be able to rent a system for $50 to $100 per day.

You will need a feed from the mixing console so make friends with the engineer mixing the event. They should be able to supply one or two mono feeds. Remember, house sound is typically mono so stereo is unlikely. If you can only get one mono feed, be sure to have a splitter on hand to split the feed into two outputs.

With multi-camera shoots, it is common for one of your cameras to maintain a wide shot that you can periodically cut to. Ideally, you will set this camera up near the console and get a hard-line program feed from the mixing engineer. This should go directly into the wide shot camera so that you have some truly usable audio. Use the second mono signal (or use the splitter) for the transmitter and station it in a place that will not impede the signal: high up, perhaps on a pole or shelf. Each receiver will be attached to a remote camera and fed into the audio input of one channel.

With this approach, all of the cameras will get the same audio on one channel. An occasional RF hit on this feed is not a problem because you have a clean hard-line send going to the wide shot. On the other channel you should input the camera microphone for each respective camera. This will ensure that you have some signal if the wireless fails (Plan B).

Start recording on all of the cameras at the same time. This can be achieved with a simple countdown: 3, 2, 1… record! You should now be within a few frames of sync between all cameras.

If you desire a visual sync point, have someone clap their hands once record is rolling while all of the cameras gather around and simultaneously record the slate. Leave them in record during the entire tape or you will loose sync. Each time you start another tape, you will need to re-group to get the visual slate.

To remotely sync a subsequent start-point use walkie-talkies with headsets and do a verbal countdown so that everyone starts at the same time. The walkie-talkies have an additional benefit in that the director can communicate to the camera operators to be sure only one camera is re-framing at a time. This will help tremendously in post as all of the other cameras will have a locked down shot while the moving camera is resetting the shot.

As customary, be sure that the time-code for each camera begins with hour 1 for tape 1, hour 2 for tape 2, and so forth. Label each tape with A, B, C, etc to denote the particular camera. When you get into post, simply line up the audio waves on each AV file and you will be in sync. When you are in sync you will hear a slight phasing in the audio but no noticeable delay. Once video is in sync, use only the audio from the wide shot camera.

You are now ready to go!

Comments

Re: Recording Multi-cam Audio
by Malcolm Matusky
Tape? what's tape? ;-)

I have been shooting with 2 cameras for a while (dslr's) and have been using plural eyes to synch the cameras to the multi-track audio, working great for me. One note, as I am not using "time code" I make sure all the "clocks" on the cameras, and audio recorder are withing a second or so, then import to my NLE using the time as a reference point, that gets things in relative synch, plural eyes handles the rest. I do not "slate" as I generally work alone, to date, no synch problems, but if it were a noisy environment this might not work, as a audible, but not high quality, track is necessary on each camera to work with plural eyes. The only audio recorded to the cameras is a "reference track" as the on board mic is terrible and there is no decent input on the camera, I did just buy a Rode video mic pro and will use that on one camera as a backup, but still record all my sound with a 6-track field recorder using a few different mics so I can choose in post what is working best.

Cheers,

Malcolm
http://www.malcolmproductions.com
Recording Multi-cam Audio
by John Livings


Very Informative,Thanks.

Mahalo, John


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