Input Devices ‘n’ Stuff Like That...

LINE INPUTS

The term line level is defined as a standard voltage for the audio signal outputs of many pieces of sound equipment. -10dBV (or 0.316V rms) is the generally-accepted standard for so-called "semi-professional" equipment, and +4dBm (or 1.23V rms) is the generally accepted standard for "professional" equipment. Technically any voltage over 25mV rms is considered "line-level," but in the modern audio world we use the -10dBV and +4dBm references. Line-level outputs can come from equipment such as cassette decks, CD players, DAT decks, MD players, DAW computers, and the list goes on. Outputs from mixing desks and subsequent pieces of equipment are also line-level.

A line input is an input designed to receive line-outputs, at either standard, and probably any signal that exists between the two standards. Most mixing desks will provide either a separate input connector, or a pushbutton switch, by which it knows to accept the line-level signal. In theatre, one would presumably connect some sort of playback device to a line input on a desk and use it for background music or sound effect playback.

As a very basic practical note, remember when plugging things in that line-levels are much "stronger" than microphone levels; if your mixing desk is expecting and microphone-level signal, and you feed it a line-level signal, one or more circuits on your desk are going to overload, resulting in distortion. While distortion in and of itself will not necessarily harm the mixing desk, if subsequent pieces of equipment are powered on and active, severe distortion in loudspeakers can be damaging, not to mention annoyingly loud. If you have to patch equipment while the equipment is on (which is not a wonderful idea), keep all level controls down.

So, what are some things we might be connecting to an input?

RECORD PLAYERS / PHONOGRAPHS / TURNTABLES

When records are manufactured, a special equalizer takes most of the low-frequencies out of the audio signal, and boosts a lot of the high-frequencies before the record is pressed. When the record is played back, the low-frequencies are re-equalized in, and the boosted high-frequencies are filtered down. This equalization is referred to as the RIAA Equalization Curve. A separate preamplifier unit, performing the necessary equalization changes, and amplifying the output from the record stylus, is required. The preamplifier will probably terminate in -10dBV outputs for connection to other audio equipment.

The outputs from popular playback gear, such as DAT decks, MiniDisc machines, Compact-Disc machines, computer-based audio workstations, and the like all have line-level outputs. Depending on the piece of gear, the outputs may be unbalanced -10dBV signals or +4dBm balanced signals. Unbalanced outputs usually terminate in 1/4" TS jacks or RCA (Cinch) jacks, whilst balanced signals usually terminate in three-pin XLR-type connectors or 1/4" TRS jacks.

INSTRUMENTS

Electronic instrument levels are comparable to line-level signals. Generally, they are unbalanced semi-pro -10dBV signals. If the destination, i.e. your mixing desk, is in close proximity to your keyboards, samplers, tone generators, drum machines, or other electronic devices, then there is very little reason not to take an output directly out of the instrument and connect it directly to a line input on the mixing desk. If, however, it is necessary to place the mixing desk far away from the instruments (i.e. in the case of orchestra pit to front-of-house), one should use a direct box in order to rectify impedance differences between the instrument and the mixing desk, and to take the high-impedance -10dBV unbalanced signal and convert into a low-impedance microphone level balanced signal.

Direct boxes are devices that convert unbalanced -10dBV level outputs into balanced, microphone-level inputs. They are used heavily in sound reinforcement, when it is necessary to drive long runs of cable between instruments and the front-of-house mixing desk. Its operation is quite simple-- take an output from the instrument in question and patch it into the "Input" on the direct box. A "Link" output of the direct box allows daisy-chaining of the instrument output into a local amplifier or mixer arrangement. The "Output" of the direct box, usually an XLR connector, is the microphone-level balanced output, which is run to the front-of-house mixer. Direct boxes can also have other options-- an internal attenuator pad switch, a low-frequency rolloff switch, and/or a ground lift switch. Attenuator pads can aid in reducing the level at the mixing desk from a hot signal, an LF rolloff switch can aid in cleaning up low-frequency garbage, and ground lift switches can aid in rectifying potential (ha ha!) ground loops-- if audio equipment is grounded in too many places, a loop of potential difference will form, and will induce a hum into the audio system. The ground lift switch will disconnect the shield of the microphone cable from the direct box, thereby eliminating one possible loop point.

MICROPHONES

The term microphone level is the level, or voltage, of signal generated by a microphone, usually somewhere around 2mV. Compare this number with that of the two line-level specifications (0.316V rms and 1.23V rms), and you see how significant the difference is. The output level from a microphone is this small due to the size of the transducer element-- a very small amount of air pressure moves a very small, thin diaphragm through a small magnetic field. The resultant signal is also very small. In order to cleanly process, mix, and divide the microphone-level signal, we must use a preamplifier to boost the miniscule audio signal from the microphone to approximately line-level so that the signal may be manipulated at a decent level. Microphone preamplifiers, or "mic pres", are commonly found inline on the input channel of most mixing desks. There are also standalone units whose sole purpose is to amplify microphone-level signals to line-level; the use of external mic preamps is often noticed in studio sound recording, where every bit of quality counts.

There are thousands of different types of microphones available... and every single one has its own electrical, mechanical, and tonal qualities that make it suited for one or another type of application. Let's discuss.

As we discussed previously, microphones convert air pressure fluctuations into electrical energy. So how do they do that? Well, there are a couple of different methods. One of the most common types of microphones is the dynamic microphone. The dynamic microphone works very much in the same fashion as a loudspeaker-- except in reverse. A flexible diaphragm is mounted to a coil of fine wire. The coil is mounted in the air gap of a magnet such that the diaphragm-and-coil are free to move within the air gap of the magnet. When a sound pressure wave strikes the diaphragm, the diaphragm-and-coil vibrate in response; the coil moves back and forth within the magnetic field provided by the magnet. As the coil moves back and forth through the lines of magnetic force, a small electrical current is induced in the gap. [This is standard electromagnetic physics.] The magnitude and direction of the induced current is directly related to the motion of the coil; thus the current is an electrical representation of the sound pressure wave which struck the diaphragm. If you want to learn all the wacko mathematics and physics formulas that describe this phenomenon of induced electrical current, consult your local physics professor, not me.

Dynamic microphones are very durable. They are extremely common in rock-and-roll sound reinforcement or in other instances in which they may be subject to shock or extreme environmental conditions. They are are good, all-purpose microphones that have predictable characteristics and low cost.

Another type of common microphone is the condenser microphone. The condenser microphone operates by creating an electrical capacitor whose capacitance varies as a function of the sound pressure wave. A thin diaphragm is stretched in front of a metal disc, called the backplate. The diaphragm and backplate do not touch each other, but are very close, and thus create a capacitor, or condenser. When a sound pressure wave strikes the diaphragm, the distance between the diaphragm and the backplate changes, thus changing the capacitance of the condenser. If the capacitor system is given a fixed electrical charge (called "polarizing voltage"), changing the capacitance of the condenser will proportionally change the backplate voltage as a function of the sound pressure wave. The backplate voltage, then, is the audio signal. In order to create the fixed electrical charge, an external voltage must be applied to the microphone, which is customarily done through the use of a battery pack, or, more commonly, through the use of phantom power, voltage sent via the microphone cable from a microphone preamplifier or the mixing desk.

Condenser microphones are slightly less durable than their dynamic counterparts, so they are not used as much in rock-and-roll situations, where they may be susceptible to shock. In orchestral reinforcement, however, their sound quality cannot be beaten by a dynamic microphone. In theatrical sound reinforcement, you may find condenser mics anywhere-- in the orchestra pit, on actors themselves as part of a wireless microphone system, as shotgun (rifle) microphones, or as foot (float) microphones.

A variant on the condenser microphone is the electret-condenser microphone, which does not require the polarizing voltage, but they do require a power supply for an in-line preamplifier (so instead of using phantom power for the polarizing voltage, they use the phantom power for the in-line preamplifier). The in-line preamplifier brings the audio signal level of the diaphragm to a level comparable with normal microphone levels.

Condensers and dynamic microphones are by far the most popular types of microphones used in sound reinforcement; however, if one delves into recording one may find ribbon microphones, which exhibit very smooth audio and electrical qualities, but are infamous for being very delicate microphones. Carbon microphones exhibit very poor audio quality but are very inexpensive to manufacture and are very durable; older telephone handsets used carbon mics for these very reasons.

Physical differences between microphone design help dictate for what use a given microphone may be used. By the far the most prominent microphone design is the handheld microphone, which is designed to be held by a speaker or a singer, or which can be clipped to a microphone stand. Most handheld microphones have very good shock isolation to prevent handling noise and vibrations from marring the sound quality.

Stand-mount microphones are specifically designed not to be handheld. Shotgun (or rifle, in the UK) microphones are examples of stand-mount microphones, and are primarily used atop boom arms or tripods for film and video production. Other types of microphones are merely mounted on tripod stands for orchestral recording or reinforcement. Podium microphones are designed to be rather inconspicuous in design and are generally mounted to lecterns or podiums in order to provide a clean, professional appearance, especially when on camera.

Lavalier microphones are by far the most popular type of microphone in theatrical sound design. Lavalier mics are comprised of very small microphone elements, usually electret-condenser type, designed originally to be pinned to clothing or hung around the neck. As theatrical sound design has progressed, provisions for mounting the lavalier microphones in hair, over the ear, or sewn into clothing have all come into play in order to hide the microphone upon the actor. As technology moves forward, we are seeing advances in moisture resistance and reductions in size, which make the lavalier-type microphone even more prevalent in theatrical sound reinforcement.

Contact pickups are microphones, technically speaking, but instead of picking up sound pressure waves through the air, it picks up sound pressure waves through a given medium, such as a sounding board on a musical instrument.

Pressure response microphones, trademarked "PZM" for "Pressure Zone Microphone" (™ Crown International), are microphones that use a flat plate to increase gain. The microphone element itself is placed extremely close (< 5mm) to and facing a flat plate. In theory, the microphone samples pressure variations in the tiny air gap between the element and the plate, rather than responding directly to sound pressure waves traveling in air. In practice, the microphone element picks up direct sound waves and reinforces those with the sound waves reflected off the flat plate, which act together to produce excellent response. A variation of the PZM microphone is the PCC, for "Phase Coherent Cardioid," (™ Crown International), which uses the same principle, but only halfway-- the design of the microphone produces a directional microphone (see "cardioid," below).

Polar patterns, also called pickup patterns, describe the way in which a microphone element will respond to sounds at different frequencies coming from different directions. Think of the polar pattern as the targeting range of the microphone in question. It is a polar graph that displays the pickup pattern on all four axes (0°, 90°, 180°, and 270°).

Omnidirectional microphone elements, as their name implies, pick up sound pressure waves more or less equally from all directions. Omnidirectional microphones are used often in recording studios and in other situations in which gain before feedback is not of great concern. They are also the preferred type of lavalier microphone used in theatrical sound reinforcement, mainly because the omnidirectional polar pattern does not emphasize the resonant low-frequencies of the chest cavity-- the phenomenon of low-frequency emphasis is known as the proximity effect.

Probably the most popular type of microphone capsule, or element, is the cardioid element, also known as a unidirectional pattern. While the omnidirectional microphone element is more-or-less equally sensitive to sound coming in from all directions, the cardioid element is most sensitive to sounds coming in along its main axis (0°), and rejects sound waves coming in along its rear axis (180°). The cardioid pattern rejects some sound from the side axes (90° and 270°). The directional characteristics of the cardioid capsule make it an ideal choice for sound reinforcement applications in which system gain and the reduction of feedback are primary concerns. Because of their directionality, one can "aim" the microphone at the sound source in the best possible fashion in order to reject extraneous noise; however, cardioid microphones tend to introduce more colorations to the sound because the capsule responds to different frequencies differently. Directional microphones tend to boost the low-frequency content of sound sources when the microphone capsule is very close to the sound source, called the proximity effect, which makes a directional microphone preferred among vocalists who know how to control their voices.

A derivative of the cardioid pickup pattern is the supercardioid pattern. The supercardioid rejects less sound from the sides than a cardioid microphone, but it has a small rear lobe at 90°. They are used in situations in which greater side rejection is necessary, but some rear pickup is tolerated. The supercardioid microphone also has greater directionality from the front, and are often used as shotgun, or rifle, microphones in video and film sound production.

Similar to the supercardioid is the hypercardioid pattern, which is more sensitive to on-axis sounds than the supercardioid, rejects almost all side noise, but has a somewhat larger rear lobe at 90°.

A slightly stranger but very useful pickup pattern is the figure-8 or bidirectional microphone. As the name implies, bidirectional microphones are most sensitive to sounds coming in along the front or rear axes (0° and 180°), but reject sounds from the sides (90° and 270°). They may be used in reinforcement situations in which two adjacent instruments require microphones, such as in between two tympani drums in an orchestra pit.

WHAT'S THE FREQUENCY (RESPONSE), KENNETH?

When applied to microphones, the term "frequency response" is a measure of the accuracy with which the microphone transfers a given sound pressure into a given audio signal at different frequencies. An ideal microphone would translate a given sound pressure level into the same audio signal (electrical) level, no matter what the frequency-- within the audio range, of course, approximately 20Hz to 20kHz). Such an ideal microphone would be described as having a flat frequency response.

While some test instrument microphones and some recording microphones may approach this ideal, most of the microphones used in professional sound exhibit anything but flat response. However, it must be noted that some variations in frequency response are not necessarily eschewed-- the Shure SM-58, for instance, a very popular vocal microphone, has a slight boost in the mid-high frequencies around 2kHz to improve intelligibility. This boost in the upper frequencies is known as a presence peak, and many vocal microphones exhibit this quality. Such a deviation from a flat frequency response then becomes a good selling point. As we approach the lower end of the frequency spectrum, it is not uncommon for a microphone's frequency response to fall off sharply below 100 Hz, especially in the case of vocal microphones, which is generally not looked down upon, since the human voice is generally incapable of producing such low frequencies. The dropoff of response at low frequencies also helps eliminate extraneous noise. However, for instrument uses and for testing purposes, response to 50Hz or lower is necessary. It is important when designing and selecting a directional microphone that the frequency response remain relatively flat off-axis. Even though the sensitivity drops, it is necessary to maintain the same tonality if the instrument in front of the microphone should shift off-axis.

While the presence peak is usually something manufacturers can control, an effect known as the proximity effect is something that is inherent in all directional microphones-- it is an increase in low-frequency response when a directional microphone is very close to the sound source. When less than two feet away from the source, the effect can produce up to 16dB of increased low-frequency energy. Well-trained announcers and vocalists often use proximity effect to add "fullness" to the sound of their voice as part of their microphone technique. Those who are untrained and "eat" or "swallow" the microphone may contribute to distortion or decreased intelligibility in public-address applications.

BE SPECIFIC!

A few important-sounding terms will undoubtedly be introduced when shopping or spec'ing a microphone. You should know the basics of what they mean when you read a microphone's specifications, and how they can affect how you use each type of microphone.

The source impedance of a microphone is the equivalent total AC resistance to current flow that would be seen looking into the microphone's output. The source impedance dictates to what type of input the microphone can drive without having detrimental effects on the tonal qualities of the microphone. The generally-accepted rule-of-thumb dictates that a microphone should be connected to a load whose input impedance is about ten times the microphone's source impedance; thus, a microphone with a 150 ohm source impedance would ideally be connected to an input with a 1.5kohm input impedance. Microphones are generally divided into two types of impedance classes: high-impedance and low-impedance. Most professional microphones used on the stage and in the studio are low-impedance microphones. The source impedance of low-impedance microphones is generally below 150 ohm; thus, they should be terminated by a ~ 1.5kohm source impedance. Inexpensive microphones used for karaoke machines and whatnot, and contact microphones or guitar pickups, are generally high-impedance, with source impedances around 25k ohm or greater. Low impedance microphones have become the preferred standard in stage sound and sound recording since, when used properly, they are far less susceptible to noise interference pickup in the cable. To be properly utilized, the input to which the low-impedance microphone is connected usually has a transformer, or other electronically-balancing device. Low impedance microphones can drive cables hundreds of feet long, whereas high impedance microphones are limited to approximately twenty-five feet before noise pickup becomes unacceptable. It is worthwhile to note that microphone impedance does not necessarily have a direct relationship to price and/or quality; it is merely a characteristic that one must weigh like any other microphone characteristic.

We discussed balanced and unbalanced connections in a previous chapter, so we won't dwell on this topic. As with all audio signals, microphones can appear in balanced or unbalanced systems. Balanced connections are almost always used for low-impedance microphones, and most always appear terminating in a three-pin XLR connector. Unbalanced connections are used for high impedance microphones and guitar pickups, and usually terminate in a 1/4" phone connector. Microphones in professional work should use a balanced system whenever possible, due the noise immunity of the wiring system.

Phantom power refers to a powering system used for microphones that require an external power supply, such as condenser microphones. Some condenser microphones have built-in battery packs either in the microphone itself or at the connector end; these microphones can usually accept phantom power in addition to the battery pack. Most mixing desks will supply phantom power of 48v DC, although the microphones themselves can usually accept anywhere from 1.5v DC to 50v DC-- but check with the microphone in question to be sure. In a phantom power system, the supply voltage is placed on both of the signal lines in a balanced wiring scheme: the positive voltage is sent down the positive and negative legs of the audio signal, and the shield is used as the voltage return connection. Theoretically, then, dynamic microphones connected with phantom power are protected from damage, since this type of wiring system results in a net zero DC potential across the dynamic element. Be careful of using phantom power via an unbalanced system, as the results could be rather electrifying. Certain direct boxes require power, and certain types don't, so be sure to read the instructions!

Transient response is a measure of a microphone's ability to handle and properly deliver very quick musical attacks and signal peaks. The response is mainly dictated by the mass of the diaphragm in question-- a diaphragm with more mass will respond less quickly to quick signal changes; condenser microphones and ribbon microphones generally exhibit better transient response than dynamic microphones. When shopping for a vocal microphone, good transient response is generally not a big deal, but it becomes a big deal with percussive or plucked musical sources.

Maximum SPL is a specification that defines the level of the loudest sound the microphone can handle without becoming overloaded, resulting usually in some sort of distortion. It is important to note that the microphone capsule is often blamed for distortion in a sound system when in fact the microphone is overloading the preamplifier stage to which it is connected. A professional microphone should be able to handle sound pressure levels of at least 130 dB SPL without overloading the capsule-- that is the threshold of pain: very, very loud. The peak level from a well-trained rock vocalists may approach 130 dB SPL; however, when close-micing percussive instruments, sound levels may approach 140 dB SPL, so a microphone capable of withstanding 150 dB SPL or more should be chosen. Note that when using condenser microphones, the overload point will be decreased if a lower phantom power voltage is applied; if your battery-powered condenser microphone becomes distorted for no apparent reason, replace the battery. Condenser microphone specifications usually provide a reference phantom power level, i.e. "Maximum SPL: 137.32 dB SPL at +48V DC."

GAIN!

Gain in a sound system is the amount of amplification or additional level obtainable in a sound system, quantifiable in decibels or as power or voltage ratios. Proper system structure, proper microphone placement, and proper loudspeaker placement will all help to maximize a sound system's acoustic gain. Briefly, when dealing with microphone-cum-loudspeaker placement, we should keep the distance between the microphone and the loudspeaker as large as is humanly possible, keep the distance between the microphone and the sound source as small as possible, and use directional microphones and loudspeakers, well-placed so the interaction between the two is minimized.

It is logical that as one adds microphones to a sound system, the potential acoustic gain will decrease. When quantified, every time you double the number of open microphones (i.e. microphones that are on), the system gain is 3dB closer to feedback. When operating a sound system, then, it is important that only those microphones that are required be turned on, and those that are not required are turned off. Additionally, while it can sometimes benefit a sound recording by using eight microphones on the drumkit, it may be necessary that only three are needed in a reinforcement situation.

Good microphone placement when micing musical instruments will help increase a system's overall gain. While in recording work, it is often desired to capture room "ambience" and all sorts of good psychoacoustic phenomena within a room, in live work it is desirable to close-mic instruments as much as possible. When a close-micing technique is used, the microphone "hears" a higher acoustic sound pressure level, which translates into a higher voltage, which provides for a cleaner signal at the mixing desk, and consequently through the rest of the system. Ambient noise pickup is reduced in a close-micing situation, which provides for better gain-before-feedback.

When micing vocalists, it is important that the designer or operator educate the uneducated in proper microphone technique. Public speakers or vocalists who "eat" the microphone, stand three feet away from the microphone, or nervously shift from side-to-side are big culprits; for the stubborn, the only solution may be to use a lavalier microphone, which, while providing less-than-optimal system gain, at least travels with the talent as he or she wanders further and further away from the lectern.

GREAT, SO WHAT KIND OF MICROPHONE SHOULD I USE?

Here we will provide you with some common microphone applications, and some suggestions for particular microphones. If we should mention particular manufacturers and model numbers, please note that they are merely opinions; we do not mean to leave anyone out, and we do not receive any sort of promotional kickback. Although... I could use another Sennheiser cigarette lighter...

Vocals, solo- for most rock and roll situations, a cardioid handheld microphone is the preferred choice. Some vocalists and engineers prefer hypercardioid or supercardioid cousins. For theatrical musicals, if the aesthetic of the director is not harmed with handheld microphones, then a cardioid handheld wireless microphone is a good choice, provided the vocalist(s) in question have been properly edu-mic-ated. The operator will usually have tons of system gain, much more than would be found when using a lavalier microphone. Popular handheld microphones for vocalists are the ubiquitous Shure SM-58, the condenser Shure SM-87, a series of handhelds manufactured by Audix, and the occasional Sennheiser.

Vocals, drama and musical- when the aesthetic of the show does not allow microphones to be visible by the audience, we turn to lavalier microphones with wireless transmitters, mounted in various and sundry ways to the actors, often colored and painted to blend into hair or skin tones. In the early days of theatrical sound reinforcement, the Sony ECM-55, 66, and 77 were popular-- they were large but sounded acceptable. In the mid 1980s, Sennheiser released their world-reknowned MKE-2 lavalier microphone, which was available in a few different colors to accommodate hiding the microphone. The capsule was no bigger than a pencil eraser, and the frequency response and sensitivity of the microphone were much-improved over earlier counterparts. Lavalier microphones manufactured by Tram, Crown, and more recently by Countryman Associates, Sanken, Brüel and Kjaer, and AKG are available these days and all provide different desirable characteristics. The best bet? Listen.

Vocals, choral and musical- more and more productions call for groups of singers to be miced en masse, whether in dramas as professional actors are no longer trained to project their voices, or in musicals for large ensemble scenes where it is impractical to put all the performers on wireless lavalier microphones. Even classical opera, known for its use of professionally-trained singers who can project, is incorporating concealed microphones into its art. In order to mic a group, or sections of the stage, a technique known as area micing is used. As the name implies, certain sections of the stage are miced; the operator mixes the show by using only the microphones aimed at the areas of the scene. Two types of microphones are generally used for area pickup: foot or floor mics, and rifle or shotgun mics. Floor mics, as the name implies, are usually cardioid condenser microphones designed to be mounted on a flat surface, such as a floor. Using the floor as a reflective surface, the microphone uses the reflected sound waves and the direct sound waves hitting the microphone capsule to increase the amount of gain it provides. Two preferred types of floor microphones are the Crown PCC-160 and Shure SM-91. Before there were floor mics, designers used to affix (super-, hyper-) cardioid condenser microphones, usually those designed for instrument micing, to the floor, aimed up in an orientation similar to footlights. It is generally accepted that an odd number of floor mics, spaced evently along the edge of the stage, provide tolerable area pickup (an odd number ensures that there is a microphone directly in the center-- often an important acting area; it is the job of the designer, having chosen to area-mic a show, to pay attention to blocking and specific acting areas that may be difficult to pick up with convential area-micing techniques). The AKG C-451 was a popular choice in those days; some were aimed at the floor to replicate that response found in modern foot mics, often using foam mounts called "mice". Similar microphones could also be mounted to stage rigging for area pickup, or suspended from the ceiling. Popular choices were the Sennheiser MKH-816 or ME-80, originally designed for boom-micing in film production. Remember that most of the intelligible frequencies of the human voice are high, and thus directional, so pointing microphones straight down, hung from the flies, is ineffective as a reinforcement tool; it is thus best to aim rifle or shotgun mics such that they "aim" at about performer head-height. Designers might also find it worthwhile to hide microphones within practical set-pieces; using a wired lavalier microphone in a potted plant, for instance, may provide satisfactory results... as long as no one tries to water the plant. Your results may vary.

Music, acoustic strings- most stringed instruments benefit greatly when miced with a good-quality condenser microphone. Engineers and designers have long preferred condensers as the microphone usually captures more subtle nuances of stringed instruments than their dynamic counterparts. As one proceeds from higher-frequency instruments, such as the violin, to lower-frequency instruments, such as the violoncello, it is usually wise to use a somewhat larger-diaphragm microphone to fully reproduce the lower frequencies of the instrument. Violins and violas are very receptive to microphones such as the AKG C-451/460, Sennheiser ME-40/MKH-40, or the Neumann KM-184. In situations where more gain is required than can be achieved with a condenser mic on a boom arm, a wired lavalier microphone clipped on to the bridge of the instrument or attached to the performer's head. For violoncellos and acoustic basses, the veritable AKG C-414 microphone is a great choice, not to mention the Neumann U-87. Grand pianos are traditionally miced with a pair of condenser cardioid mics, one aimed at the higher strings, and one at the lower strings. Upright pianos have been miced with a variety of techniques, usually somewhat dependent on the actual tonal quality the designer is trying to achieve; a microphone pointed at the instrument's sounding board will provide a clearly-defined sound; by adjusting the actual placement of the microphone, a more "honky-tonk" rock-and-roll sound quality can be achieved. Contact pickups can be substituted for microphones in many situations, but tonal quality will suffer somewhat in exchange for much higher gain. Some acoustic bass players prefer contact pickups because they can control their individual style very easily. Acoustic guitars are very receptive to cardioid condenser microphones as well in an orchestra pit situation at a relatively close distance (one foot). For a more "open" sound with more finger and fret noise, the microphone should be positioned further away at the expense of system gain.

Music, acoustic winds and brass- cardioid condensers work very well to mic wind instruments. As with stringed instruments, large diaphragm microphones lend themselves very well to micing lower-frequency wind instruments. Some designers prefer using condensers to mic brass instruments, while others feel that the condensers are too sensitive, resulting in too crisp a sound, and instead use dynamic microphones. Again, this is a stylistic choice-- let your ears be the judge.

Music, drums and percussion and other things that are struck- some prefer condenser microphones for drumkits, and some prefer dynamics; most rock-and-roll kits are miced with dynamic microphones, whilst more jazz-based, more instrumentalas opposed to percussive kits are miced with condensers. Depending on the application and desired outcome, one may find it necessary to mic most of the kit individually at close range, using many boom mics and clip-on mics, while in other situations a single overhead microphone and a kick drum mic may suffice. Kick drums are best miced with a good, large-diaphragm dynamic microphone, such as the AKG D-112; other manufacturers make similar mics designed specifically for kick-drum use. Orchestra-based percussion, such as tympani drums and concert bass drums, are very happy with a large-diaphragm condenser mic; marimba, xylophone, and various percussive toys are happy with a standard condenser microphone. When inputs are at a premium out front, consider a lavalier mounted overhead, or even on the performer to mic a full percussion rig.

Music, electric instruments- hours can be spent arguing over the benefits of direct-injection versus amplifier micing when it comes to electric guitars and electric bass guitars. Some guitarists maintain that micing their amplifier is the only way to properly produce their quality of sound, while designers, intent on keeping the SPL level of the orchestra pit to a minimum, prefer to direct-inject the guitar directly to the mixing desk. Again, it is a stylistic choice based on the performer's style, the musical style, and the designer's desired outcome. Hours can be spent arguing over the different microphone placements when micing a guitar amplifier, but the gist of it is to put the microphone in front of the amplifier, or use a direct box to convert the high-impedance instrument output to a low-impedance level for the mixing desk. 'Nuff said.

Other- general stage pickup is useful to bussing to dressing rooms, the lobby, and the hard-of-hearing loop. When not a dedicated mix output from the mixing desk, a rifle microphone mounted to the balcony rail can provide satisfactory results, especially when audience response is desired in the mix.

Again, these are just suggestions and starting points. Let your ears be the judge! That about covers possible input types. We will discuss wireless microphone application in a separate chapter.


Continue to Mixing Desks. Return to the Sound Index. Jump to Wireless Microphones.

Comments, Questions, and Additions should be addressed via e-mail to Kai Harada. Not responsible for typographical errors.
http://www.harada-sound.com/sound/handbook/input.html - © 1999 Kai Harada. 07.11.1999.

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