Instant Digital Audio

VASST Instant Series

Douglas Spotted Eagle

• Publisher: Routledge
• Year: 2005
• eBook ISBN:
  9781136063817
• Topic: Media & Performing Arts
• Subtopic: Film & Video

The rapid drop in costs of digital audio recording and production tools has led to widespread adoption by "non-audio" people. Multimedia producers, including videographers and graphic designers producing for the Web and other media, need to learn the many details of producing digital audio. Hot topics include selecting and using recording hardware including microphones, headphones, and monitors; how to use postproduction-editing software; and how to deliver the finished audio in an array of media/formats. Instant Digital Audio presents digital audio principals and techniques for the non-audio specialist. Videographers and multimedia producers who are new to audio learn how to select the hardware and software that they need and how to use it. Straightforward explanations supplemented with ample screenshots and technical data address recording and production topics including microphones and relevant applications, best practices in recording audio, and how to feed audio into the computer for editing. Postproduction topics include setting up a studio, acquisition and editing techniques, filtering, and restoration.

Chapter 3

Microphone Types and Placement

Sound is 70% of the picture experience, and 100% of the radio or CD experience. Microphones are the first tool used in the recording process.

Microphones may be very simple, yet very complex. On the simpler side of the microphone, it’s basically a speaker in reverse. If you apply voltage to a speaker, it makes sounds that you can hear. If you apply sound to a microphone, it generates voltage that the receiving device can hear. Speakers are often used as microphones, even today. One great method of recording big bass sounds is to take a large speaker and wire it with microphone connections, place it in front of a big bass rig or kick drum, and use it in combination with other mics or direct boxes to record the bass or kick drum.

There are several considerations when choosing a microphone for your recording needs. One consideration is the ability of the microphone to accurately reproduce the original sound as it is converted from audio waves to voltage.

Most microphones today are reasonably faithful once you pass a median price point, and it becomes a matter of “personality.” Each mic manufacturer has their own “personality” that some users will like, and others won’t necessarily appreciate.

Another consideration is “speech intelligibility.” This is the term used to describe how comprehensible voices are in a recording. In the 1K to 3.5K frequency range, human hearing is particularly perceptive (or not, depending on age) and this is one place that various microphones have varied sensitivities. Many of the microphones recommended in this section have slight boosts in this range for greater intelligibility. Of course, EQ and other techniques may be employed to boost these frequencies as well, but we like to have the mic capture the sound with the boost so that we’re not adding anything to the signal later in the process.

As you might guess, there are several types of mics available, and of course their price ranges reflect this as well, with mic costs starting in the sub $100.00 range going up into the several thousand dollar price points.

There are three basic mic types, and in those three types, there are several designs that utilize aspects of each of these mic types.

Microphone Types

Dynamic mics - Mics that generate their own power. These mics are found everywhere, in every situation, from rock stages to cheap computer microphones. Some types of dynamic mics have been around for years.

Ribbon Mic - Use a very thin strip of metal between two magnets. As sound waves strike the ribbon/thin metal strip, induction causes the sound waves to be converted to electrical energy.

Condenser mics - One of two plates is charged with a current. As the distance between the plates increases/decreases due to sound waves striking them, the energy is changed, thus creating the current required to reproduce sound. There are a variety of condenser microphones, such as the piezo-electric and the electret condenser.

For the moment, we’ll focus on average mic designs that fall from the above three categories, as they apply to most uses in video and general audio.

Shotgun mics - Named for their appearance, not for their characteristics.

Lavaliere mics - The type that is often hidden, used by interviewers the world over, and used on most television news broadcasts.

Stick mics - Mics that go on a stand, such as seen on most music stages and in the hands of field journalists.

Boundary mics - Mics that are placed on an object and in many cases, use the sound characteristics of that object to “help” the mic hear audio better.

The Shure SM 58 is a common dynamic mic. Far from fragile, the running joke in the rock music industry is that you can drive nails with one. Dynamics are by far the most common and familiar type of mic. The dynamic mic works by having a plate coupled to a coil (known as a diaphragm) move over a magnet when pressed upon by air pressure, creating voltage. This voltage is passed from the mic to a preamplifier, usually found in a mixer or camcorder, and amplified to a level where the voltage is sufficient for a mixer or camcorder to process and record or reproduce. In fact, if you view a cross section of a speaker, and the cross section of a dynamic microphone, they look quite similar.

Some mics have a magnet made of neodymium. This allows the magnet to be smaller, lighter, and have greater frequency response and higher output.

Dynamic mics are available in an extremely wide variety of types, brands, and price points. This mic type is very good for high SPL (sound pressure level) and general-purpose use.

Condenser mics use an outside power system, sometimes built into the mic in the form of a battery compartment, while others use an external source. The external source may be a camcorder, mixer, or powered box that sends voltage down the line. This is known as “phantom power.”

Condenser is another word for “capacitor” as this type of microphone uses a capacitor to convert acoustic energy into electrical energy.

The condenser mic has two plates as opposed to the single plate of a dynamic. One of the two plates is charged with voltage. Depending on the mic, it could be the front or back plate. When sound waves strike the front plate, it moves against the distance between the two plates, generating voltage.

The external voltage allows the plates to be very sensitive, and typically capable of outputting higher voltage from the mic, reducing the need for a high amount of preamplifier gain, cutting down on the noise generated by the preamplifier, and typically providing a cleaner, more accurate sound.

The device illustrated provides phantom power to condenser mics that don’t use batteries and there is no mixer available or necessary on the shoot.

Electret condenser mics are similar to a condenser, but don’t require external power; the power required is built into the mic in the form of a capacitor, acting somewhat like a permanent magnet. Therefore, no batteries or phantom power are needed.

As a general rule, condenser mics are not optimal for high sound pressure levels, as the extreme sensitivity of the mic can make it susceptible to distortion in extremely loud circumstances. One other drawback to condenser mics is that their sound quality is affected by weather/humidity. Keep them dry, and in their cases. Usually, condenser mics come with a small packet of desiccant, or material that will absorb moisture. Keep it with the mic so it doesn’t rust. If the mic does get wet, carefully shake all the water out, and put near a heat source to dry it.

These mic designs may be broken down into yet more categories: the following pages describe the pickup or “listening patterns” of various types of microphones.

Pickup Patterns: This is a description of how the mic “hears” sound, based on the direction it’s facing.

Omni-Directional Mic Pattern

Omni-directional mics have a pattern just as their name implies; Omni (all) directional. These are rarely used in settings where the audio input to the mic will also be reproduced simultaneously through loudspeakers. In other words, you won’t find omni-directional mics on your favorite band’s stage during a live performance. There are two reasons for this. First, because omni’s pick up or hear everything in all directions, the sound coming from the speakers may also be picked up and cause feedback. Feedback is where the mic hears the speakers and in turn feeds more sound to the speakers and on and on it goes. Secondly, bleed from other instruments on a stage make it difficult to control what the mic hears, so if you have a person being interviewed on a rock stage, whether they are in front of or behind the drummer, it won’t matter because the mic hears the drummer regardless of what is done. The pickup pattern of an omni-directional mic is drawn as rounded when viewed on paper. (See previous illustration) Omni’s are good for interviews in a quiet stage setting, good for broadcast use, and good for recording studios where the setting is controlled and reflections from walls, ceilings, floors, and instruments is a consideration for capturing the optimum sound. Omni directional microphones may be used for stereo micing a source, as they have no proximity effect.

Bi-directional (Sometimes called a “Figure of 8 mic”)

Bi-directional mics, like their name implies, can pick up sound from two directions, typically from the front and rear of the microphone. Bi-directional mics reject sound from the sides. These are not to be confused with stereo microphones. Bi-directional mics are often used for interviews between two people. Bi-directionals are also good for recording two vocalists in a recording studio where the performance might be compromised if the singers were in different rooms or too far apart.

Hypercardioid Shotgun (sometimes incorrectly referred to as a “zoom” mic)

The shotgun mic has a fairly tight pattern that rejects sound from the side, and to some degree from the rear of the microphone. Shotguns are commonly used on boom poles and in some indoor...

Table of contents

• Cover
• Title Page
• Copyright Page
• Dedication
• Table of Contents
• Hardware setups
• Setting up the room for Great Audio
• Microphone Types and Placement
• Recording, Levels and All
• Understanding Analog vs Digital Metering
• Connecting Microphones to a Camcorder
• Effective Mic Boom Techniques
• Monitoring Audio on a Production
• Mixing Techniques
• Plug-In Tools for Nonlinear Editing Systems
• Noise Reduction
• Scouting the Location for Audio Problems
• Simple, Practical Solutions for Difficult Edits
• Understanding wireless systems
• ACIDizing Digital Audio