Try watching any movie with the sound off and suddenly there’s nothing. The importance of sound that a microphone provides can’t be underestimated, especially now that producing video or recording music or voice is no longer the province of just the movie director or sound professional.
While video devices may include a built-in microphone, the only way to capture and truly control the audio so that it sounds the way you want is through the use of an external mic. But in order to reap the benefits of what a microphone can offer, it’s necessary to understand not just the different types of mics that are available but also their underlying technologies.
Types of Microphones
Microphones come in physical configurations that include handheld, lavalier and hyper directional. One of your biggest distinctions will be: the area around a microphone that collects sound, which is called the pickup pattern.
These patterns include:
- Omnidirectional: sound is picked up equally well from all directions, the flat response being good for news reporters out in the field
- Bi-Directional: commonly called a figure-8 pattern, example: capturing a performer and live audience simultaneously
- Cardioid (or Unidirectional): sound is picked up mostly from the front, popular for live sound as it can be pointed away from sounds not wanted and focused on a single source such as vocals or a musical instrument
- Supercardioid/Hypercardioid whose pickup patterns reject more sound coming from the sides and rear than cardioid patterns, a prime example includes the shotgun mic for greater reach for a source farther away and used in film, location video and TV shows
- Specialty: one very specific pattern is a parabolic mic whose sound quality is not as important as its ability to reach distant sources, for example: gathering football action from players who are more than 100 feet away
The mic capsule is where the “element” resides for gathering and converting the sound waves into electrical signals. There are a number of different elements available today, for example, condenser mics which have a high frequency response and a high transient response (ability to reproduce “speed” of voice/instrument). These require an external power supply and their sensitivity to sound will find them being used for live music venues. Condenser mics employ either a small diaphragm, which works well for concert recordings, or a large diaphragm that can provide a warmer sound for studio vocals.
Dynamic microphones, on the other hand, are many times more durable than condenser mics and don’t require a power supply. Their frequency response is however more limited than condenser mics and they are less accurate in sound reproduction. Loud guitar amps and drums are their forte, due to their ability to withstand sound pressure at high volumes.
Electret condenser mics do not need a power supply as they use a permanently charged material. Each of the following three types of electret differs in how the electret material is used:
- Foil-type uses a film as the diaphragm and is the most common but of lowest quality
- Back electret is where a film is applied to the backplate of the mic capsule and the diaphragm is made of an uncharged material.
- Front electret is the newest type in which the backplate is eliminated and the condenser formed by the diaphragm and the inside surface of the capsule (the electret film being adhered to the inside front cover). While no polarizing voltage is needed, a small amount of power is required to handle an integrated preamp, frequently phantom powered in sound reinforcement and studio applications or through the use of a 1.5-volt battery in the mic’s housing. Front electret can be found in microphones being used for high-quality recordings as well as those of lavalier mics and even in small devices.
Another transducer type is the ribbon mic; a type of dynamic mic using a thin aluminum, duraluminum or nanofilm ribbon placed between the poles. These microphones are typically bi-directional and well suited for miking instruments such as acoustic guitars and brass instruments. No power is required for their operation. Their fragile nature, however, makes them better suited for studio use than in the field.
Wireless mics are more complex than wired, as a transmitter must be integrated into the microphone or connected as an external pack. Radio-frequency interference can be minimized or eliminated altogether by a receiver featuring “diversity” technology. This is where two antennas are receiving the signal, with one taking over for the other should there be too much noise in the reception. Since wireless helps you be free of cables, on-location and outside uses are where they will most often be found. It’s also important to note that the characteristics of the microphone itself are not changed whether wired or wireless.
Selecting from among the different types of mics will enable a "capture" of the sound that is most relevant to you. To do this, a number of technical factors must be considered as they impact sound waves. There is the output impedance, which measures the AC resistance at the microphone and must be matched by the input, so using a low-impedance mic with a high-impedance input is verboten. Low impedance mics, by the way, are well suited for most of the current recorders and mixers now available and also avoid the loss of highs and output levels when traveling through cable. This is unlike high-impedance mics, which have a practical limit of about 20 feet of cable.
The level of sensitivity of the microphone must also be considered, as is the choice between balanced and unbalanced output. Balanced output mics are far less susceptible to radio frequency interference as well as pickup of hum and other electrical noise than that of unbalanced mics. Consumer camcorders typically are limited to unbalanced mics, using the standard 1/8-inch jack rather than the 3-prong XLR jack found with pro mics.
For casual users, the video being shot often relies on the camcorder or DSLR’s built-in mic. But while that might do for creating ambiance when panning across a family gathering or a day at the beach, it is woefully inadequate when it comes to singling out an individual since the microphone is picking up everything that is going on around it (and in some cases, even the sounds being generated by the camcorder too). Also, the camcorder’s built-in mic is not a great choice for adding any commentary afterwards. Through the use of an external mic, wired or wireless, the sound will become clearer and have a greater presence than would otherwise be the case. Here are two examples.
Azden SMX-5 DSLR: Shoe mounted stereo mic [$80]
Designed for use with DSLR cameras, the compact vertical shape belies its stereo recording capabilities, the placement of the mic elements takes away camera noise. The stereo electret condenser provides a frequency response of 100-20,000Hz, there is a low signal-to-noise ratio and it runs for 1,000 hours on a single AAA battery. Also, an integrated shoe-mount holder and a removable windscreen are included.
Audio-Technica ATR2500-USB: Cardioid condenser USB mic [$100]
As a large diaphragm side-address condenser mic, this USB mic can be used for recordings ranging from home studio to field recording to voice over and even podcasting. It utilizes a high quality analog to digital converter for a 16-bit, 44.1/48kHz sampling rate and the cardioid polar pattern reduces side and rear sounds. Front-mounted controls are joined by a built-in headphone jack with volume control for direct monitoring of the output without any audible delay. Compatible with PC and Macs, a tripod to hold the mic at your desk is included.
The steps between the “casual” videographer and the more advanced one can be dictated by what is being shot. Covering a wedding or a family reunion requires more precision than just following the dog around in the backyard. By the same token, capturing the sound requires more control over what is being heard. This is where an external mic comes in, since the physical design as well as internal characteristics can be tailored for the recording that is being made. Two such microphones follow.
Shure PG24/PG58: Wireless vocal system
This handheld microphone has been tuned to accentuate the clarity needed for those speaking as well as for those singing (vocals, both lead and backup). Utilizing UHF wireless technology, the single-channel receiver can select from up to five channels and features 1/4-inch and XLR outputs. Audio reception is accurate at 24-bit 48kHz through with two receivers and antennas for a solid signal.
Que Audio Q 210: Video shotgun mic kit
This shotgun mic's compact shape keeps it out of the shot while providing full size rejection features. Optimized to reject side and rear sounds, the results are a focused pickup pattern without mechanical or off-axis noise. It has a high sound pressure level, with a full 20Hz to 20kHz frequency response. The microphone is 48-volt, phantom powered, and utilizes a supercardioid back electret.
The new breed of professional camcorders provides a quality image suitable for such uses as broadcast and live event recordings. Since the caliber of the audio must match that of the video, this necessitates a professional-grade mic. These microphones may have no more of a learning curve than their less expensive brethren, but a high level of quality has been imbued in them for handling any task with reliability and competence.
Sennheiser SKM 5200
This professional-grade wireless mic comes in a robust housing and enables sensitivity adjustable in 1dB steps. It has interchangeable capsule support and operates for up to eight hours on two AA batteries or a rechargeable battery pack. There are three selectable low cut filter frequencies and the 36MHz bandwidth is switchable across the UHF spectrum (450-960 MHz). A backlit LCD display integrated into the mic allows for easy navigation of menu options, using a jog dial.
RØDE NTG3: Precision RF bias condenser shotgun mic
Featuring a supercardioid polar pattern, this professional-grade directional mic is highly suitable for film, TV, ENG or wherever high resolution broadcast audio is needed. It possesses a high sensitivity and a full frequency response, has 50 percent less self-noise than the majority of shotgun mics in the field and as a result of the RF bias technology, it is almost completely moisture resistant. The microphone is machined from solid brass, yet is lightweight at less than 6oz. There’s no need to be restricted to the use of a built-in mic, not when there are so many different types of microphones on the market.
Selecting the microphone that best suits your needs whether it is wired or wireless, handheld or shotgun, cardioid or electret, requires careful research. Do the research and you won’t be surprised with the sound you’ll hear when the video plays.
Mobile Devices and Microphones
Mobile devices, such as smartphones and tablets, are gaining popularity as recording devices due to their convenience and portability. There are a number of requirements for any microphone being used with these types of recorders. The microphone should have a narrow pickup pattern, so that it focuses on the sound in front of it, leaves out the background, and provides adjustable sensitivity (gain) for how loud or quiet the source is. The addition of a headphone output enables the operator to hear what is being picked up by the microphone without any delay. Microphones have been designed with mobile devices in mind, for example, Blue Microphones’ Spark Digital, does not require a powered hub or an accessory in order to connect to the mobile device. These mics are also designed with shock absorption in mind to provide protection for their use in potentially hostile environments.
Marshal M. Rosenthal is a technology and consumer electronics freelance writer.