Guide Audio Systems A Shure Educational Publication Audio Systems Guide for Video Production By Christopher Lyons
Video Production Guide Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 The Audio Chain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Microphones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Cables and Connectors . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Mixers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Connecting to Camcorders . . . . . . . . . . . . . . . . . . .
PREFACE B ecause the video production field is enjoying such rapid growth, keeping up with its technological advancements is a real challenge. The equipment used in video production is becoming more sophisticated, practical, and accessible every day, and more and more people are getting involved with video projects of all kinds. Shure has been deeply involved with the audio side of video production for many years.
THE AUDIO CHAIN A lmost everyone has used a simple cassette tape recorder at one time or another. In that instance, the process of recording sound is very simple: press the Record button, talk into the microphone, and press the Stop button when finished. In the world of audio-for-video, however, there may be many pieces of equipment between the microphone and the videotape recorder. This series of devices is collectively known as the audio chain.
If you were asked to describe the kind of car you drive, you might answer in terms of make, body style, or color. Similarly, microphones are commonly described by four criteria: physical design, directionality, transducer type, and electrical impedance. Each of these characteristics carries its own special significance to the microphone’s overall suitability for various purposes.
Lavalier — Another popular mic for video use is the lavalier type. Historically, the word “lavalier” refers to microphones which are hung on a cord around the wearer’s neck, but the term has grown to include almost any small microphone that attaches to the user’s clothing. Lavalier microphones leave the talker’s hands free to gesture, hold notes, or demonstrate a product.
Concealing a lavalier microphone — In some productions, it is necessary to conceal the microphone. It is important to prevent both the microphone and the first few inches of cable from rubbing against either the body or clothing, which will cause noise. Here are some options: • Under the shirt collar. The mic is lightly taped to the inside of a dress shirt collar, near the opening in front. The cable can be routed around to the back of the neck, over the collar and under the shirt.
Double-miking with lavalier microphones is usually achieved with a special tie clip or bar that holds two microphones. (Note: When wireless microphones are used, each lavalier mic must be connected to its own bodypack transmitter. These two transmitters must be on different operating frequencies, and their signals must be picked up by two different receivers, as discussed later.) Surface Mount — These microphones are designed to work on a flat surface.
Tips on Using Shotgun Mics: Shotgun mics can be positioned either slightly above, below, or to the side of the sound source, so that the mic does not appear in the camera frame. Try to avoid aiming the mic at a hard surface, such as a tile floor, brick wall, or hard ceiling. These surfaces reflect sound waves, and may reflect background noise into the microphone or cause the sound to be slightly hollow. A heavy blanket can be placed on a reflective surface to provide some temporary sound absorption.
circular. This can be advantageous, since one omnidirectional microphone can be used to pick up voices from several directions, as long as each person talking is approximately the same loudness and the same distance from the microphone. The handheld microphones used by news reporters are usually omnidirectional, allowing the reporter and interviewee to be picked up by one microphone held between them.
TRANSDUCER TYPE As mentioned earlier, microphones serve just one purpose: to convert sound waves into electrical energy. The part of the mic that actually does the conversion is called the transducer or cartridge. But different types of transducers perform the conversion in different ways, and each type of transducer has certain characteristics that make it more or less suitable for various applications.
Condenser microphones offer several benefits. The most important of these is that they can be made very small, which is why all miniature lavalier microphones are condenser types. Condensers tend to be very sensitive to the extreme low and high frequencies, and usually have a very crisp, clean sound. Their built-in preamplifiers allow condenser mics to provide higher output than dynamic mics, meaning that for a given sound level, a stronger electrical signal comes out.
PHANTOM POWER A little earlier, we talked about the fact that condenser microphones require electrical power to operate (usually between 11 and 48 volts DC). Phantom powering is a method of supplying that power through the microphone cable from a remote supply. This supply can be a stand-alone unit or may be incorporated in the audio mixer, or, in some cases, the video recorder. It is called "phantom" power because it comes from somewhere outside the microphone and is not supplied by a battery.
Wireless Microphone Transmitter Camcorder with Receiver Audio chain incorporating a wireless microphone system The low-band VHF (49-72 MHz) range is utilized by radio-controlled toys, cordless telephones, baby room monitors, and other consumer products. Wireless microphone systems on these frequencies — particularly 49 MHz — are likely to pick up interference from some of those items.
between UHF and VHF wireless microphones. Due to their more complex design and circuitry, however, UHF systems are typically more expensive than comparable VHF systems. It should be noted that UHF and high-band VHF frequencies are reserved by the FCC for use in broadcast and film/video production, but it is the responsibility of the purchaser to observe FCC rules regarding their use.
Example of a wireless diversity system (Shure UC Wireless shown). body or mounted directly to a small mixer or camcorder. A short cable connects the audio output of the portable receiver to the audio input of the mixer or camcorder. Better models offer a separate headphone output, so that the camera operator can monitor the audio through headphones or an ear piece. A wireless microphone system which includes a portable receiver is a very handy thing to have on a video shoot.
Wireless in-ear or “personal” monitors can be used in a variety of ways in the broadcast or video production environment. Reporters in the field can hear questions and answers from the broadcast studio; the narrator of a video program can listen to a prerecorded script while simultaneously reciting it (sometimes called an “ear prompter”); an actor can hear stereo music playback while singing along; a presenter can hear questions picked up by audience microphones.
CABLES AND CONNECTORS C ables and connectors are probably the most overlooked link in the audio chain, and yet poor quality cables and/or faulty connectors are frequently the cause of major audio problems. There are basically two kinds of connections used between audio devices: balanced and unbalanced. A balanced connection requires a cable with two wires (one for the “hot” signal and one for the “return”) enclosed by a shield of metal foil, braid, or mesh.
Another popular audio connector is the male 1/4 inch phone plug, which mates with the female 1/4 inch phone jack. The name originates from use of this connector on early telephone switchboards. These can be found on cables used with almost any type of audio equipment: headphones, loudspeakers, amplifiers, signal processing gear, and microphones.
turntables (as well as tape decks, CD players, and so on) to home stereo equipment. Phono plugs are really not designed to be inserted and removed over and over again, as doing so will eventually result in a broken or intermittent electrical connection. At that point, the usual procedure is to throw the cable away and buy a new one; the problem is that you never know when it’s going to happen.
MIC AND LINE — WHAT DO THEY MEAN? Some mixers have switches on the rear panel for setting each input or output jack for mic level or line level. These refer to the signal level or intensity that the input is designed to accept. A mic-level or microphone-level signal is the amount of voltage that comes out of a microphone when someone speaks into it - just a few tenthousandths of a volt. (Of course, this voltage varies somewhat in response to changes in speaking volume and source-to-mic distance.
AUTOMATIC MIXERS Problems often arise when multiple microphones are used for recording or sound reinforcement. As more microphones are added, pickup of reverberation and unwanted room noise increases, which decreases intelligibility. In situations where a sound reinforcement system is being used, additional microphones also increase the likelihood of feedback or “howling”. These problems cause listener fatigue, as it becomes necessary to concentrate harder to comprehend the talker’s message.
The mixer’s tone oscillator and meter can also be used to establish consistent levels among several pieces of audio gear. For instance, during setup, the mixer’s tone oscillator could be turned on, and the mixer’s Master Output level control adjusted so that the mixer’s output is set at a known level (as indicated on the level meter). The input of the recorder connected to the mixer would then be adjusted until its level meter indicated the same level as shown at the mixer.
FP33 FP22 FP11 Examples of a portable stereo mixer (Shure FP33 shown above), headphone monitor (Shure FP22 shown bottom left) and mic-to-line amplifier (Shure FP11 shown). CONNECTING TO CAMCORDERS C onnecting a microphone with an XLR connector to a mixer input with an XLR connector is simple. Things can get more complicated when you must interconnect balanced and unbalanced devices, mono and stereo devices, or devices with different types of connectors.
as to avoid contact with it. Professional condenser microphones requiring phantom power cannot be directly connected to a camcorder; a separate phantom power supply is required. • If the camcorder is stereo, are there separate mono input jacks for the left and right channels, or a single stereo input jack that feeds both channels? If there are separate mono jacks, do they supply DC power.
Connecting microphones to camcorders Dealing with Automatic Gain Control Most consumer-grade camcorders and some industrial models have an Automatic Gain Control (AGC), which adjusts the audio level up or down as necessary. The AGC circuit is designed to compensate for the fact that the sound source is often far from the microphone on the camera. An external microphone is usually placed much closer to the source, however, and therefore a much higher signal level is fed into the camera’s input.
HOW TO HANDLE SOME COMMON MIKING SITUATIONS F ollowing are some hints on choosing the right mics for some common audio/video applications. In most situations, there is no single “right way” to do it, but some ways may be better than others. In some cases, you may decide to sacrifice some sound quality in order to gain some other, more important benefit, such as accommodating your subject’s refusal to wear a lavalier mic. There are some general ground rules that always apply, however: 1.
Situation #2 — The Product Demo Shot: This time our speaker is demonstrating a product on a table. Before you decide what type of microphone to use, stop and think for a moment.
Picking up audience questions is a perennial problem for audio people, primarily because there is no really effective way to do it. For their comments to be intelligible, you have two choices: bring the audience to a microphone, or bring a microphone to the audience. In other words, you could place a mic on a stand somewhere in the room and ask people to move to that location if they have a comment.
Unidirectional Omnidirectional Two methods for miking a conference table TROUBLESHOOTING N o matter how well you plan ahead, sooner or later you will probably run into an audio-related problem. To help you out in those situations, we’ve listed some of the more common problems encountered in doing audio-for-video, along with some possible solutions. 1. Buzz, hum, crackle, and other noises — These are almost always caused by an electrical problem somewhere in the system.
the signal to the balanced, low-Z configuration. You can then plug the mic into a balanced mic input or use another transformer to convert the signal back to high-Z to match the equipment’s input. It’s important that the transformer is used as close to the microphone end of the cable as possible, so that the majority of its length is balanced. Placing the transformer at the mixer input will not make the mic cable more resistant to electrical noise. 2.
4. “Popping” and wind noise — Popping is caused by an explosive sound wave striking the microphone diaphragm, such as that which occurs when a talker says words beginning with the letters “p” or “t”.
A FEW FINAL WORDS T he most important thing you can do to improve the audio quality of your productions is plan ahead. When you walk into a room to begin setting up your equipment, take a good look around you. Identify things that might cause a problem with your audio (such as air conditioning ducts) as well as those which you might be able to use to your advantage (such as sound absorbent carpeting in one section of the room).
MORE RESOURCES Finally, we’ve included a reading list for those of you who would like to learn more about the technical aspects of audio. The resources below are comprehensive, yet for the most part do not require that the reader have an extensive technical background. Bartlett, Bruce Stereo Microphone Techniques, Focal Press, Boston, MA (800-366-2665) Bore, Dr. -Ing. Gerhart Microphones for Professional and Semi-Professional Applications. Gotham Audio Corporation , New York, NY.
MIXERS POWER REQUIREMENTS PHANTOM POWER SPECIAL FEATURES 1 XLR 2 AA batteries Yes; 12-volt or 48-volt Mic-to-line level 1 XLR mic/line 6 XLR mic/line AC or 3 x 9-volt batteries Yes Distribution amp FP22 1 XLR mic/line 2 1/4" line 2 1/4" jacks 2 minijacks 1 x 9-volt battery — Stereo headphone amplifier for monitoring FP33 3 XLR mic/line 2 XLR mic/line (left-right) 2 x 9-volt batteries Yes; 48-volt also 12-volt A-B Stereo; very low noise FP42 4 XLR mic/line 2 XLR mic/line (left-right
MICROPHONES MODEL PHYSICAL DESIGN PICKUP PATTERN ELEMENT TYPE IMPEDANCE SPECIAL FEATURES SM58 Handheld Cardioid Dynamic Low Crisp, clear sound, very reliable SM63L, SM63LB (black) Handheld Omni Dynamic Low Great interview mic; heavy-duty shock mount MX183 Lavalier Omni Condenser Low Small size; bright sound MX184 Lavalier Supercardioid Condenser Low Directional pattern rejects noise MX185 Lavalier Cardioid Condenser Low Directional pattern rejects noise SM89 Shotgun Lin
ABOUT THE AUTHOR Chris Lyons is currently the Marketing Manager at Shure Communications, a subsidiary of Shure Inc. In his 17 years with Shure, he has served in several positions in Marketing and Applications Engineering. Chris has presented hundreds of audio training seminars to groups in the field of broadcasting, education, government, and audio-visual production, both in the U.S. and abroad.
Additional Shure Publications Available: • Selection and Operation of Personal Monitor Systems • Selection and Operation of Wireless Microphone Systems • Microphone Techniques for Sound Reinforcement • Microphone Techniques for Studio Recording These educational publications are available free of charge, as are brochures and catalogs on our full line of sound reinforcement and recording products. To request your complimentary copies, please contact us.
