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Understanding Microphones

Understanding Microphones

by Charles Hardy and Doug Boyd

Choosing the appropriate microphone for your interview is just as important as choosing the right recorder.  Different microphones serve very different purposes and will yield very different results. For decades, oral historians have been recommending the use of external microphones in order to achieve high-quality results.  Even though many portable digital recorders are now manufactured with high-quality condenser microphones built in, it is difficult to get a high quality recording from internal microphones in an interview setting. The closer the microphone is to the source of the sound the better the signal will be. Oral history, by definition, has at least two sources of audio being recorded. Unless the interviewer and the interviewee are sitting uncomfortably close to each other, the internal microphones on your digital recorder will typically not be as effective as two separate microphones or a well-placed, professional-level external microphone in between the interviewer and the interviewee. While you could place the recorder in between the interviewer and the interviewee, this would, more than likely, move the recorder out of reach for easy adjustment. Best practice is to use external microphones when possible and for the interviewer to be very familiar with the microphone being deployed and its optimal use.

Microphone Types

The dynamic microphone

  • Not as sensitive as condenser microphones
  • Much more durable than a condenser microphone
  • Does not require an external power source

The condenser microphone

  • Much more sensitive than a dynamic microphone
  • Much more fragile than a dynamic microphone
  • Requires “phantom power” for basic operation. This is an external power source, whether being supplied by a battery or from the recorder or camera. Typically, a higher-end recorder will supply “phantom power” but this usually needs to be enabled in the settings.

Microphone Pickup Patterns

Microphones are designed to work in particular situations and differ in the effectiveness and efficiency of their directionality. The directionality of microphones are classified into certain polar patterns. The polar pattern of the microphone refers to the sensitivity of a microphone in a given direction. Common patterns of microphones include cardioid, uni-directional, omni-directional and shotgun.  As a general rule, the more focused a microphone is in terms of directionality, the less ambience will be recorded.

Omni-directional: Omni-directional microphones record equally in all directions. This also means that they record much more noise than other polar patterns. These are good for single microphone, or microphone-in-between, placement during an interview.

Cardioid: Cardioid microphones pick up in a heart-shaped pattern directly in front of the microphone. This is a very common microphone type in oral history because the cardioid pattern accepts sound far more readily from the front rather than from surrounding inputs. Normally, this microphone type requires a microphone for each sound source as off-axis sound will not be picked up as effectively.

Shotgun: Shotgun microphones have an extremely focused polar pattern that is considered extremely directional.  These microphones are typically long in form and focus directionality of pickup on a direct line pointing to the source. They are very effective in static situations where the subject will not be moving much. Because they are so effective at rejecting ambient noise, they can also lose signal if the subject being recorded moves or turns away from the microphone. These are becoming more common, especially for recording video.

Microphone Connectivity

Typically, microphones tend to be classified into the professional and the non-professional categories. One of the differentiating factors in this distinction is in how the microphone connects to the recorder. There are three primary types of connectivity:

  • XLR
  • 1/8 in. mini-jack (headphone jack)
  • ¼ in jack

XLR microphone inputs are typically associated with higher-end preamps on the recorder as well as with higher-end microphones. The 1/8 in. mini jack microphones are typically associated with portability, but also with lower-end preamps on the recorder side. The ¼ in. microphone jacks are rare on portable recorders. You may want to avoid these, simply because you will probably require an adapter. If you can afford to do so, and your recorder will allow, it is recommended that you use an XLR microphone for recording. This can directly impact your choice in digital audio recorders or cameras.

How a Microphone “Hears”

It is important to understand how a microphone “hears” in order to optimize recording. Microphones hear differently than our ears. Sound and light intensity both fall off at a rate equivalent to the square of the change in distance from the source. What this inverse square law means is that small changes in distance can make large differences in sound levels. Cutting the distance in half between the microphone and your narrator’s mouth will increase the volume by a factor of four. If, on the other hand, your interviewee moves back two feet and thereby doubles the distance from the microphone, the sound level is reduced by a factor of four. This can not only make the voice sound distant and hollow, but also enable ambient sound to overpower the voice and create a very “dirty” or noisy recording.

Placing a microphone too close to a narrator’s mouth causes another set of problems, including the recording of the same breath and mouth sounds that you would hear if you stuck your ear right up to somebody’s mouth. Also known as “tight miking,” this can also cause proximity effect, the tendency of microphones to amplify the low frequencies that make a voice sound bassy and the words hard to distinguish. (Omni-directional microphones are less susceptible to proximity effect, enabling them to be moved in closer to the sound source without distortion.)

Never place a microphone directly in front of someone’s mouth, for our mouths send forth p’s and t’s in deafening, 70 to 80 mph bursts of wind called “P-pops” or “plosives.” Keeping the microphone down by the chin will solve the P-problem, but will not protect against t’s and k’s which go almost straight down. It is also wise not to place a microphone parallel or at right angles to hard surfaces, such as tables and walls. Sound waves from the same source bouncing off of hard surfaces and arriving at a microphone at slightly different times will cancel each other out, creating acoustic phase cancellation, which is heard as distortions in the recording.

Microphone Placement

Microphone placement, then, is a balancing act. To obtain a clean, high-fidelity recording, the best place to position your microphone is 6 to 12 inches from your narrator’s mouth, tilted slightly up or down and slightly off to one side (off-axis) and pointed at the corner of the mouth. Adjust microphone distance from the desired sound source according to the level of background, or ambient, noise. The louder the background noise, the closer you want to place the microphone. The quieter the background noise, the farther you can move the microphone away to avoid mouth sounds, plosives, and proximity effect. Unless you are using a shotgun mic, however, you should not move your microphone farther than 18 inches away from your narrator’s mouth. During your practice interviews, use a ruler or tape measure to see how far away you are letting your microphone out from your narrator’s mouth. And remember: If your voice sounds better on the recording than your narrator’s, you need to work on your microphone technique.

Hand-Holding Your Microphone

There will be many times when you need to hand-hold your microphone, such as recording narrators on the move, interviewing people at public events, and recording sound effects or soundscapes. Hand-holding gives you exact control over microphone placement, but to do it effectively you will need to practice. Avoid fast movements and use microphone distance as a volume control, moving in for whispers and away from louder sounds. Beware of handling and wind noise. Any hand movements or taps on the outer shell of an uninsulated microphone will appear on your recording as a rushing noise, which is why most microphones are designed to be used on stands and not held in your hand. Omni-directional microphones are designed to be hand-held and have built-in shock mounting and windscreens that permit hand-held and outdoor recording. A windscreen is a must for outdoor recording. Many microphones also have a low-frequency, roll-off switch that reduces some of the wind and handling noise. The roll-off switch can be a useful device, but it is no panacea. It will suppress the recording of all low frequencies, and can make your recording sound a bit flat.

If you hand-hold a microphone that does not have built-in shock mounting, you will need to practice holding it very still or to place it on a pistol grip. To learn your microphone’s response to wind and handling noise, practice with it indoors and outdoors. Remember, too, that your microphone cord can also conduct sound.  So make sure to not let it flap around or rub against clothing or any other surfaces.

Ambiance and Acoustics

Every space has its own unique sound characteristics, or ambiance. The hard reflective surfaces dominating in “live” rooms (rooms with hardwood or tile floors and little fabric or furniture) make recordings sound boomy and echoey. Rooms filled with curtains, sofas, rugs, and other soft materials create “dead” spaces that soak up sound can make a recording sound flat. What this all means is that microphone placement needs to be adjusted to fit the space. The basic rule of thumb is that the boomier the room or louder the background noise, the closer you should place the microphone.

Lavaliere Microphone Placement

If you do choose to use a lavaliere, clip or pin it near the collar. Running the microphone cable under your narrator’s outer garment will reduce the chances of handling noise and of the cable catching on something.  Remember to listen through your headphones to make sure the microphone is not picking up body noises or static electricity from clothing.

So Which Microphone is the Best?

It depends. Many broadcasters and oral historians use lavaliere microphones. They are easy to use, let your interviewee move around without moving out of microphone range, and– once clipped on– are all but invisible and easily forgotten. Lavaliere microphones are the most convenient and unobtrusive way of placing a microphone close to the speaker’s mouth and achieve a low-noise recording. Lavalieres do, however, have some limitations. Because they rest against the body, most lavalieres have built-in, low-frequency cutoffs or attenuators that reduce boominess but also limit their dynamic range. Placed close to the body they can sometimes pick up growling stomachs, pacemakers, and static.

Because they are placed under the chin rather than pointing directly at the mouth, placing lavaliere microphones cannot be as exact. Perhaps the greatest drawback is that they cannot be used to record anything but the spoken voice. For about the same money, a full-size omni-directional microphone placed close to the source will generally produce a rich recording and is infinitely more versatile, allowing hand-held and non-voice recording. The drawback of single, omni-directional microphone placed in between interviewer and interviewee is that they will pickup more ambient noise than if you utilized two mono microphones placed much closer to each speaker.

The interviewer plays a critical role in the oral history interview so the recording levels of the interviewer should not be neglected. Ideally, there is a closely placed microphone on both the interviewer and the interviewee. For this reason, it is recommended that you use two microphones in a professional recording context. Common combinations of this configuration include two lavaliere microphones or two mono, cardioid condenser microphones.

There are many microphones to choose from. No matter which one you possess, the important thing is that you get to know how your microphone works and can be flexible enough to adapt to your recording situation. Which microphone you choose depends on context.

  • Where will you be recording the interview? If it is a noisy environment, choose a directional microphone. Will you be outside or inside? If outside, make sure you have a windscreen.
  • Will you be mounting the microphone on a stand or will you use a hand-held microphone? If hand-held, you must have a microphone designed for ENG, or electronic news gathering. These are the microphones that you see reporters holding on television. They contain internal shock mounts to minimize handling noise. If you were to hold a typical condenser microphone in an oral history interview, the handling noise would overwhelm the recording. Dynamic microphones are less sensitive to handling noise. However, if you will be conducting an interview with a hand-held microphone, it is recommended to purchase an ENG-designed microphone, which has been engineered specifically for hand-held recording. If the interview goes mobile, such as in the situation where someone will be speaking while walking, ENG microphones are critical, as is the interviewer’s ability to keep up with the interviewee to maintain close proximity.
  • Who will you be recording? If for a moment you anticipate that your microphone or microphone placement will make the interviewee uncomfortable, compromise. Lesser recording quality may be the better option if an interviewee is made uncomfortable by the presence of a microphone placed in their face. However, we find that this is very rare as the microphone tends to blend into the background within minutes of beginning the interview.
  • How will you and the interviewee be physically arranged in the interview? Optimal seating positioning is critical for optimizing recording quality.

–  If you are sitting across a large table, best options include two mono microphones, two lavaliere microphones, or an omni-directional microphone in the middle.

–  If you are sitting closely at a corner of a table, one cardioid or omni-directional microphone will suffice.

–  If you are sitting side-by-side with someone in a living room situation and there is no table between you and the interviewee, placing the microphone in close proximity to the speaker can be very difficult. Even tables in this configuration can be lower, end tables, which still place the microphone a great distance away from the speaker’s mouth. Lavaliere microphones work very well in this situation. If you are not using lavaliere microphones, this configuration may require a boom stand-mounted microphone to get the microphone closer to the speaker’s mouth. This can also be useful for conducting interviews with bed-ridden individuals who cannot comfortably sit in a chair.

Microphone Strategies

Certain microphones work better for certain recording scenarios. It is important to understand that your choice in microphone will have both advantages and disadvantages. Eventually, you will want to invest in a second microphone that will give you the capability to adapt to your recording situation.

A dynamic microphone will not be as sensitive as a condenser microphone. A condenser microphone will also be much more fragile than a dynamic microphone so if you are rough on your equipment, think about a dynamic     microphone.

A directional microphone will perform better in a noisy environment. For these recording situations, choose a cardioid microphone. Shotgun microphones are getting more popular for recording oral histories but they require some practice to optimize use.

Lavaliere microphones work great unless the interviewee is wearing a starched  shirt or lots of jewelry. They also require significant “setup” time before the interview to make sure you are optimizing placement on the body and negotiating jewelry and clothing.

Two mono microphones placed in front of each speaker will provide a richer and lower-noise recording than a single microphone placed in the middle.

As indicated in the name, omnidirectional” microphones record in all directions. This is useful for recording multiple individuals, however, omnidirectional microphones will pickup up much more ambient noise in the recording as opposed to a more directional microphone.

Microphone Accessories

Unless you use a lavaliere, your microphone(s) will need to be supported. Many sound documentarians insist upon hand-holding their microphones. This gives them exact control over microphone placement and the ability to make instantaneous adjustments to the movement of an interviewee’s head. For oral historians conducting interviews than can last hours, hand-holding is impractical, so microphones supports become necessary.

Microphone Supports and Shock Mounts

A table stand may be the simplest and most inexpensive support for your microphone, but it is not the best. How often, for example, can you find a flat surface that keeps a full-size microphone the required 6 to 18 inches from your narrator’s mouth? Sound waves reflecting off of the surface of a table or other hard, flat surface can also cause something called phase cancellation, whereby sound waves from the same source arriving at the microphone at only a micro-fraction of a second apart from each other, can cancel each other out and diminish the fidelity and richness of the recording. Table stands can also conduct sound waves up the post of a microphone, through the barrel, and into the recording. To isolate your microphone from finger tapping, accidental kicks of the table, and other noises that would otherwise end up on your recording, you can use a shock mount, a clip that suspends the microphone in a rubber cylinder or rubber bands that absorb the vibrations. A very useful support designed for hand-holding a microphone without built-in shock mounting is a pistol grip with shock mounts.

One excellent microphone support for an oral history interview is a portable floor stand with a boom and shock mount. This enables your interviewee to sit wherever he or she pleases and allows you to place the microphone exactly where you want it. The use of a floor stand and boom also reduces the chances of phase cancellation and your interviewee accidentally knocking or touching the microphone stand or cable.

Windscreens

Air movements that we do not hear can play havoc with a sound recording, since a microphone transduces them as low-frequency sounds. Even inaudible breezes can sound like great gusts of wind. The human voice, too, produces hurricane-force winds in the form of p’s and t’s that explode from our mouths in 80 mph bursts of air.  The resulting plosive, or P-pops, register as loud booms on your recording. The solution to both of these problems is a simple foam windscreen placed over the head of your microphone. (Many microphones also have a roll-off switch which allows you to reduce the strength of the low-frequency signals that these pops and gusts appear as). A windscreen is absolutely essential for outdoor recording and provides an added degree of safety during indoor voice recording.

Microphone Conclusions

Remember, with microphones, you definitely get what you pay for. Low-end microphones, even when connected to high-end recorders, will produce sub-standard results. Do some research to make the best purchase for your project needs within your budget. Then, practice with your microphone. No microphone is perfect and the user must understand their microphone’s limitations and what microphone techniques will optimize your recording. Practice with your microphone and learn how it hears so that you can adapt in the field and optimize your recording. Never assume that one microphone can do it all. If you are recording numerous oral history interviews in a variety of contexts, you will eventually be better served by having multiple microphones at your disposal.

Citation for Article

APA

Boyd, D. A., & Hardy, C. (2012). Understanding microphones. In D. Boyd, S. Cohen, B. Rakerd, & D. Rehberger (Eds.), Oral history in the digital age. Institute of Library and Museum Services. Retrieved from http://ohda.matrix.msu.edu/2012/06/understanding-microphones/.

Chicago

Boyd, Douglas A. and Charles Hardy. “Understanding Microphones,” in Oral History in the Digital Age, edited by Doug Boyd, Steve Cohen, Brad Rakerd, and Dean Rehberger. Washington, D.C.: Institute of Museum and Library Services, 2012, http://ohda.matrix.msu.edu/2012/06/understanding-microphones/

This is a production of the Oral History in the Digital Age Project (http://ohda.matrix.msu.edu) sponsored by the Institute of Museum and Library Services (IMLS).  Please consult http://ohda.matrix.msu.edu/about/rights/ for information on rights, licensing, and citation. 

Permanent link to this article: http://ohda.matrix.msu.edu/2012/06/understanding-microphones/

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