Tuesday, March 2, 2010

Lavs Demystified

What are Lavs? Well, basically they are tiny mics that you clip onto your actors so that you can get audio from them when you dont have a boom, or cant get it close enough. Lav is short for the word "Lavalier" which in French means pendant or a kind of jewelry that would be clipped on like a broach.




Good sounding lavs can be very expensive, complete with a wireless transmitter and receiver easily cost over a grand each, but you can find cheaper ones. Those however are usually used for conferences and things where all you need to be is heard, and the quality of the audio isnt necessarily that important.

But it is possible to use lavs without the wireless setup. The catch is that now theres a wire involved that you have to run underneath your actors clothing, and all the way through the set to your sound mixer's mic input. This method isnt very common because lets face it, the actor doesnt want to be tethered to anyone, and having cables throughout the set can be a safety issue, let alone the fact that it may get in the shot! But using lavs wired is a good way to avoid all kinds of potential problems that can occur when using a wireless system.

Almost all lavs use wideband FM (Frequency Modulation) modulation, which means that they work like radio waves. The problem in this case is that they can often be using the same signal as a number of other wireless devices including other communication devices. On a good lav system you would have the option of scanning through the available frequencies to use, then set your transmitter and receiver to an open frequency. On some of the lower end models however you dont have this option, or if you do, you only have the option of using one of several frequencies, if the frequency isnt just set by the manufacturer.

Another issue is that if your actor has to continue his/her dialogue through lets say walking into other rooms, and the receiver (which should be with the sound guy) stays in the initial room, theres a chance that the signal can cut out. If you have ever seen Francis Ford Coppolla's "The Conversation", you see a high tech (for the time) sound guy/spy who has bugs in various places, picking up a conversation two people are having in a park. But they are walking around, and theres all kinds of things getting in the way. Later on you see him taking his various sources and making a compiled mix of the conversation the two people were having, and you hear his source tapes cut in and out. This sort of thing actually happens, though it usually takes thick walls or led paint to cut the signal completely.

The other downside to using lavs is that since they are to be clipped onto your actor, you have a high risk of getting clothing noise from your actor's movement, indirect audio because maybe the clothing your actor is wearing doesnt allow for a hidden mic clipped anywhere close to the bottom center of the neck (these two are usually the most common problems), and of course, poor sound quality because the mic is so small. They also eat batteries faster than you could imagine, and they only take good brand name batteries! I have also had interference because I could hear the actors heart beating over their dialogue!

Also, a good thing to know is that a lot of lav mics are omni directional if you are using one type of clip, and cardioid when using another. This can be the difference between an extremely high noise floor, and a good clean signal. The lav mics themselves often come in a little package with a number of different types of clips, so choosing the right clip is very important because the outcome of your audio is at stake, and there is usually nothing written anywhere to tell you this. A qualified Audio Engineer who has a good knowledge of microphones and electronics can tell just by looking at it, but most people just see several different clip options.

So with all of these negative aspects of using lavs, why bother? Well, as I mentioned in a previous article, lavs are a good backup system. Sometimes the boom just cant get close to the actor because maybe the scene requires a wide angle, or maybe the location doesnt allow for the boom to get close. This is a very normal problem on set, because "on set" doesnt necessarily mean you are in a film studio. Also, lavs can often pick up some good low end frequencies in an actors voice that may be desirable in the mix. Some actors are well known for their voice, and if the boom isnt picking up that low end, the voice might not be recognizable as that of the actor. In any case, it's always a good idea to have a backup if you can squeeze it into the budget, and your post sound guy will appreciate the options.

I work a lot in post as well, and it is nice to have multiple sources. I once worked on a film where we were shooting with the RED ONE camera, and they wanted to record the audio directly into the camera so they wouldnt have to re sync it later. Now, I have a lot of experience with that camera, and although it looks good and it's interchangeability is a cool feature, they really phoned it in when it comes to sound, which is why I recommend always recording to a different source, and to just not bother with the RED's audio. But in this case, that is what the producer wanted, and he wouldnt take "no" for an answer. So, knowing this, I said to him "then we're going to need a mixer with direct line outputs for each input". We were using three lavs and a boom, with a Sound Devices four-channel mixer, which provided direct line level outputs (I'll talk about the difference between line level and mic level in another article), because I wanted to avoid using the RED's mic pre amps. 

So even with all of this precaution, the RED (which can accept up to four analog audio sources, and record four separate audio tracks) still managed to distort most of the audio (though it was not audible at the time), which we found out once in post production. However, since we had multiple takes, and multiple audio sources, I was able to piece together the dialogue in the end and the difference was night and day. Initially, I thought we were going to have to ADR the whole film! But I was able to save the day (and the actor's patience!) by my use of all of these sources (I'll talk about Dialogue Editing in another article).

So I hope that this article was enlightening on what lavs are all about, and why they are a good idea to have, but not to rely solely on.