Two of the worst problems that plague location sound recording are RUMBLE and WIND NOISE.
Rumble can be defined as unwanted bass vibrations transmitted through objects into the mic capsule itself. Examples of rumble include ground or floor vibrations caused by nearby traffic, heavy footsteps, and building/structural vibrations. In addition to rumble, a closely related malady is that of HANDLING NOISE -- created by the friction or light tapping of human fingers, either directly against the microphone itself or conducted through whatever means by the microphone is supported (e.g. fishpole).
Merely filtering out the low frequencies at a mixing panel will not correct the whole problem. Low frequencies can quickly overload the pre-amplifiers of some microphones and most recorders. To avoid the risk of permanent audio distortion on your tracks, these low frequencies should be controlled BEFORE THE SIGNAL IS PROCESSED BY THE MIC ELECTRONICS.
The solution to rumble lies in isolating the microphone from these vibrations by some means of free-floating suspension or non-conductive insulation... which is the role of a good shockmount.
Not to be confused with shockmounts are MICROPHONE CLAMPS. Although both are intended to fulfill support functions, the difference is that a clamp is merely designed to hold a microphone -- not to isolate it from vibration. Clamps are manufactured from conductive, hard materials such as plastics and metal.
Because mic clamps (sometimes referred to as mic stand adapters/holders) are cheap to manufacture, they are supplied free with most microphones and you'll often find boxes full of them in the A/V supply rooms.
Although clamps may be acceptable for use with relatively insensitive (dynamic) mics such as those found in hotel conference rooms, they should not be used with the highly sensitive shotgun mics associated with professional film and video production.
Instead, make it a habit to always use an isolation shockmount.
A good shockmount does not have to mean big bucks. For example, the most popular shockmounts in use by the professional film and video industry sell for under sixty dollars!
Without a doubt, the overall most popular shockmount in use by the video industry is the model AT8415 "rubber band mount" manufactured by Audio Technica. This inexpensive universal shockmount consists of two pair of thick rubber bands arranged tic-tac-toe fashion within a cylindrical framework. The mic is held inside of the "center square" of the grids formed by the rubber bands.
Since the AT8415 does not utilize a plastic cradle of fixed diameter, it will support just about any mic on the market except for the long shotguns.
Extra support for longer and heavier mics is achieved by criss-crossing the rubber bands so that the mic is firmly sandwiched.
The yoke of the AT8415 is drilled and threaded to accept a 3/8" mounting screw, such as those found on standard fishpoles. An adapter is supplied for use with common mic stands and goosenecks.
The AT8415 is definitely a "best buy" considering its low profile appearance,
design simplicity, adaptability to a wide variety of mics, and excellent isolation performance.
Shockmounting a miniature microphone such as a lavalier is easier than one might imagine. It is very common to mount small mics onto table tops, walls, and all sorts of props. A short strip of cloth camera or gaffers tape, loosely wadded into a loop or a ball, will suffice. Lavalier mics have very little mass, so they are easily supported by a single thickness of tape. The cloth and adhesive gel of the tape are very efficient at dampening vibration.
An adjunct of shockmounting the microphone is to shockmount the potential source of noise and vibration. The Hollywood industry uses a material known as "foot foam" to cut down obvious trouble areas. Foot foam is adhesive backed, thin neoprene rubber which can be cut and affixed to shoes, boots, glassware, table tops, bases of mic stands, etc.
Foot foam is cheap and expendable; your dialogue track is not.
Moving up the scale in terms of quality and price brings us to dedicated pistol-grip shockmounts.
Pistol-grip shockmounts are usually designed to accommodate just one or two specific microphones. The mic mounting clips are usually specific in diameter; 19mm and 21mm are the most common. The spacing from front clip to back clip is engineered for specific mic length and mass. The rubber mounts supporting the clips are also optimized for a particular load.
The pistol-grip handles themselves are drilled and tapped to accommodate the standard 3/8" thread found on fishpoles. Some of the shockmount manufacturers also offer short fishpole mounting yokes in lieu of the handles, but the majority of users prefer the handles.
The pistol grip shockmounts sell for around $150, give or take, depending on
manufacturer, model, and your personal discount.
In general, this class of shockmounts are more fragile than the cheaper ones. However, the pistol-grip mounts are quieter and more efficient at their task, especially when it comes to the longer shotgun mics.
Pistol-grip shockmounts are manufactured by Light Wave Systems (U.S.), Rycote (U.K.) and Sennheiser (Germany).
Rycote uses a suspension style for shorter mics whereby the mic clip is hung from elastic string within a horseshoe shaped cradle. For the longer mics, the mounting clips sit on a pie-shaped wedge of neoprene rubber.
Sennheiser uses a variety of mounting systems, depending on their particular model.
Light Wave Systems manufactures what has become the most popular system on the market. The mic clips, closed O rings of plastic, sit on an inverted "V" of rubber blocks. Spacing of the mounts is individually designed for each model microphone in use by the industry.
Light Wave also has introduced a couple of newer designed mounts for studio boom applications.
Over the years, Light Wave has been very responsive to the needs of the industry, and kept refining their product into what are generally acknowledged to be the quietest shockmounts on the market. And the fact that they are located in the United States (Los Angeles) sure makes it easier to get them on the phone!
One quick note about shockmounts and thread sizes. It has been mentioned that
shockmounts come equipped with some sort of mounting hole or adapter for use with fishpoles and mic stands. There are three different thread sizes that you may encounter: 3/8", 5/16", and 5/8".
The current standard thread for fishpoles is 3/8". The slightly smaller 5/16"
used to be the standard in Hollywood, but has pretty much been replaced by the more popular 3/8". Older fishpoles and pistol-grip handles may require a simple adapter for use with 3/8".
The larger 5/8" thread size is the standard for mic stands and goosenecks. Most mic clamps are threaded for 5/8", although some are also supplied with a 3/8" insert adapter.
One of the most important differences between the inexpensive shockmounts and the pistol-grip shockmounts is that the pistol-grip mounts are designed to mate with blimp windscreens of the same manufacturer. For microphones intended strictly for indoor applications, blimp windscreens are of minor value. But for condenser shotgun mics that will work outside, the capability of attaching a blimp is a necessity.
Before we get into a discussion of windscreens, a preliminary word about WIND NOISE.
There are two types of wind noise that will affect your soundtrack: ACOUSTIC WIND NOISE and CONTACT WIND NOISE.
Acoustic wind noise is the howling that the wind makes blowing through trees and between buildings. It is a form of ambiance, just like traffic noise. Because it is background noise in our environment, it cannot be controlled by a windscreen.
Rolling off or filtering out the low frequencies will help somewhat, but howling wind is made up of a lot of higher frequencies as well, so eliminating the bass is only a partial help.
The best way to eliminate acoustic wind noise is to close mic the talent. Get the microphone in as close as you can get it, and then lower your mic gain (volume) so that dialogue dominates the soundtrack instead of background ambiance. That's really about all that you can do.
Contact wind noise, on the other hand, is that blast of distortion and audio breakup caused from wind physically striking the sensitive diaphragm of the microphone capsule. We've all heard that sound when someone blows directly into a microphone.
The distortion created by contact wind noise cannot be fixed in post-production. It can only be chopped out along with the accompanying dialogue; and a new piece of dialogue cut in to replace it.
But contact wind noise can be prevented. That's what a windscreen does.
The simplest windscreens are known as "pop filters". Pop filters may be of
either thin foam or metal mesh. Their purpose is not to defend against natural wind, but to block the exhalation from a performer, known in the industry as "breath pops".
Pop filters don't do much against real wind, but anything is better than nothing.
Thicker foam windscreens will protect against light breezes, both indoors and out. At no time should a shotgun mic ever be used without at least a foam windscreen. Even indoors, the mic can encounter moving air (wind) that would cause breakup. Air from heating/cooling systems, open passageways, and even from moving on the fishpole are all indoor wind hazards for the highly sensitive mics that our industry uses.
Another good reason to always use a foam windscreen is to physically protect the microphone from dust and accidental impact.
Outdoors, a foam windscreen will provide only minimal defense against wind noise. Foam will suffice for the less sensitive electret condenser (ENG-type) shotguns such as the ME80 and AT835, but the highly sensitive true condenser shotgun mics such as the MKH416/816 and AT4073/4071 definitely require a blimp system.
In a pinch, you can improve upon a foam windscreen by wrapping it with several layers of cheesecloth, and then containing the whole affair within a sweat sock. If you are faced with a real windstorm, anything goes... terry cloth towels, chopped off sleeves from a sweatshirt, etc. Just so long as the covering is porous.
Windscreens work by providing a barrier against moving wind. We can define windscreens as single stage barriers, two-stage, and multi-stage.
The simple foam windscreen is an example of the single stage barrier. Moving air is slowed down by the porous foam before it can strike the mic element.
The basic blimp windscreen is an example of two-stage protection. The outer mesh shell slows down the approaching air. Whatever air passes through the mesh is then further slowed down by the non-moving trapped air within the blimp screen itself.
The effectiveness of a blimp windscreen can be improved by adding additional barriers between the onrushing air and the mic element; this is known as multi-stage wind protection.
For instance, using a thin foam windscreen over the microphone INSIDE of the blimp provides a major increase of wind protection. Make sure to leave plenty of airspace between the foam and the inside of the blimp, or else you will defeat the purpose of multi-stage wind reduction. That layer of non-moving air is vital.
The other way of improving a blimp windscreen is to use a fabric or synthetic fur "windsock" over the outer shell. The use of a plush "fur" is very
effective because the "hair" tends to disperse the oncoming wind, thus reducing
velocity but also eliminating the ACOUSTIC noise generated by high wind physically striking the outer shell of the blimp.
If the budget is tight, fake fur windsocks can be fairly easily sewn together by anyone handy with a sewing machine, such as a Costumer or Wardrobe person.
Emptying a full can of ScotchGuard onto your windsock will provide protection against rain. Heavy rain or firehoses may call for a protective condom over the microphone itself.
Hollywood sound mixers often manufacture "rain hats" made from rubberized "hogs hair" to slip over the blimps. The hogs hair is a rubberized, thistle type
material that disperses the rain drops upon impact, thus eliminating the "pitter
patter" noise that the water would otherwise make when it struck the windscreen.
An important guideline to follow when using windscreens is to only use as much barrier protection as is needed, but never less than what is needed. The more stuff you surround your mic with, the more you will interfere with the frequency response and even pattern of your mic. On the other hand, not having enough wind protection will lead to contact wind noise, which is not fixable in the mix.
One saving grace is to realize that when the wind is blowing up a storm, your actors will also be shouting their dialogue, so that some loss of frequency response is unlikely to affect the (lack of) subtlety of this forced dialogue anyway. Just don't use windsocks and blimps on your indoor stuff!
Summary of all of this is...
- Always use a good shockmount and at least a foam windscreen.
- The Audio Technica AT8415 universal shockmount is fine for indoors and works with most mics except long shotguns.
- A good pistol-grip shockmount is needed for long shotguns, as well as for any mics that you will be using outdoors with a blimp windscreen. The author likes Light Wave Systems.
- Use a blimp windscreen for exteriors. A thin foam windscreen over the mic will help quite a bit. A fur-type windsock provides even greater wind protection.