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| 1/4 Wave
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To capture an equal amount of room ambience, a cardioid microphone must be placed twice as far from a source as an omnidirectional pattern microphone. Keep this in mind the next time you are trying to capture some of a room's natural sound when recording!
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| 802.11 |
A family of specifications developed by the IEEE for wireless LAN use. The standards specify wireless interfacing protocols between two or more wireless networking systems such as a series of wireless computers and some type of base station, or even just between two computers. There are several unique types of 802.11 in widespread use. These have different transmission methods and/or data rates. As of this writing the most common of these are: 802.11, 802.11a, 802.11b, and 802.11g. 802.11g systems can work with 802.11b (also known as Wi-Fi) systems by simply falling back to a slower data transfer rate. |
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| Antenna |
A conductive device designed to radiate RF (Radio Frequency – Also, see Radio Wave ) energy from a wireless transmitter , or to capture RF energy for application to a wireless receiver. Antennas come in many shapes, sizes and configurations. Some are omni directional while others have different directional polar patterns . |
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| Antenna gain |
The ratio of the signal of a directional antenna to that of a non-directional rod antenna. Used as a measure of the effectiveness of a directional antenna as compared to a standard non-directional antenna. The value is given in dB . Positive values are achieved in the direction of radiation, while negative values are achieved at the "back" of the antenna. Antenna gain is used to refer to both transmission and receiving antennas. |
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| Baxandall Tone Controls |
The most common form of active bass and treble tone control circuit, based upon British engineer P.J. Baxandall's paper "Negative Feedback tone Control -- Independent Variation of Bass and Treble Without Switches," Wireless World, vol. 58, no. 10, October 1952, p. 402. This is the formal name for the grandfather of the type of EQ controls found in most analog equipment in use today. The Baxandall design is distinguished by having very low harmonic distortion due to the use of negative feedback in the circuits, which among other things helps keep more precise control over the behavior of the op amp s. Negative feedback basically works by sending a polarity -reversed copy of the output signal back to the input of the amp. If this signal is filter ed by components that change the relative frequency content you have an active tone control. |
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| Bluetooth |
A short-range wireless technology that communicates via a frequency-hopping transceiver over the 2.4-gigahertz radio frequency, a space known as the Industrial, Scientific and Medical (ISM) band. Bluetooth was originally conceived as a low cost, low power, short-range technology that would replace cables on such devices as mobile phone headsets, handsets and portable computers. However, its promoters soon envisioned the creation of "personal area networks" in which computers could be wirelessly connected to printers, audio could be transmitted over short distances (for example, to the rear speakers in surround setups), and remote control of PDAs or other appliances could be easily implemented. Some people have referred to it as a sort of wireless USB , which is a pretty apt description in many respects. First conceived in 1994 by Ericsson Mobile Communications (now a part of Sony), by 1998 the Bluetooth Special Interest Group included industry giants Intel, IBM, Toshiba and Nokia. Today more than 2000 companies produce or are developing Bluetooth enabled products. Apple Computers incorporate Bluetooth compatibility that allows keyboards, mice and other peripherals to wirelessly connect to the main unit. While Bluetooth originally had a transmission range of only 10 meters, today, three power classes exist for Bluetooth devices, the most powerful allowing transmissions up to 100 meters. Bluetooth is a different protocol from Wi-Fi , but both occupy a section of the 2.4 GHz ISM band that is 83 MHz wide. Bluetooth uses a technology called Frequency Hopping Spread Spectrum (FHSS) that allows it to hop between 79 different 1 MHz-wide channels in this band whenever it encounters interference from other transmissions. |
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| Body Pack |
In the world of wireless performance a body pack is the device a performer wears somewhere on his or her body that houses the electronics that handle sending a signal to a remote receiver or, as in the case of personal monitoring systems, receives a signal from a remote location. Typically body packs hold a battery and some combination of electronics that do the transmitting or receiving, and amplifying. Some wireless systems do not require a body pack as all of these electronics can be housed right inside of a microphone or a small plug that can be connected directly to a guitar or other musical instrument. |
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| Dipole |
In physics, a pair of equal and opposite electric charges or magnetic poles that are separated by a small distance. This term has been adapted to cover audio and video concepts in two different ways. In audio a dipole loudspeaker contains two drivers, usually directed 180 degrees in opposition to each other and wired in opposite phase to each other. Dipole loudspeakers are often found in home theater surround systems where they serve as rear (and sometimes side) satellites. Their donut shaped dispersion pattern can be effective for enhancing the sensation of envelopment that is an important part of the surround experience. In radio and television, a dipole antenna is an aerial half a wavelength long consisting of two rods connected to a transmission line at the center. The most common example of this is the "rabbit ears" antenna that is often used to pick up local television broadcasts. Many wireless monitor and assistive listening system transmitters use dipole antennas. |
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| Diversity Receiver |
In wireless microphone applications, diversity receivers are often used to improve reception of RF signals. A diversity receiver utilizes two separate, independent antenna systems. The receiver looks at the signal coming in from the each antenna, and determines which one is the stronger. It then switches to that stronger signal. The receiver is constantly comparing to see which antenna is providing the better signal, and can quickly switch from one to the other as signal strength changes. |
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| Dropout |
In general any type of interruption in service. When using a wireless system, a dropout is an area where carrier reception falls below a usable level, which usually causes the receiver to mute (though some older units will emit very loud white noise , like an old radio tuned between stations). In tape recording a dropout is an area of tape that has no signal, possibly due to a fault in the tape’s ability to hold a magnetic charge. |
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| Frequency Agile |
A term used in the communications industry to signify equipment that can operate on more than one frequency . It sometimes implies that the frequency selection is done automatically by the device. In our industry this term is used to denote wireless systems where the frequency (or channel as it is often called) can be varied by the user. This is an important attribute for touring acts because they need to use different frequencies in different locations due to television stations and other possible interference in a particular area. |
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| IF |
Short for Intermediate Frequency. Refers to the resulting signal in a superheterodyne receiver after the incoming carrier is mixed with the oscillator signal. In other words, a frequency to which a carrier frequency is shifted as an intermediate step in transmission or reception. |
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| Image frequency |
In wireless systems using heterodyne tuning systems, an undesired carrier frequency that can produce the same intermediate frequency ( IF ) as the proper carrier frequency. While precautions are taken to filter these frequencies before they get in to the system they can still sometimes be mistakenly accepted and processed by the receiver, which will result in poor performance and interference (at least intermittently). |
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| Kilohertz (kHz) |
A kilohertz (kHz) is a unit of frequency equal to one thousand cycles per second. Hertz measure cycles per second, and kilo means one thousand. Thus five-kilohertz is five thousand cycles per second. kHz is most commonly used in reference to radio frequencies and audio signal processing. These measurements in audio most frequently pertain to the audio spectrum (audible from around 20 Hz to 20 kHz), although hertz is a generic term, which may be applied to any analog waveform be it electrical, audio, visual, wireless signals, or other. |
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| LED |
Abbreviation for Light Emitting Diode. It is not an acronym. You do not pronounce it as "lead." It is pronounced EL - EE - DEE. An LED is an electronic component that glows when current passes through it. LED's are found in all sorts of electronic equipment these days from watches to laser disc players (in fact the laser that reads the disc is usually an LED). The lights that glow on top of your keyboard are almost surely LED's. The numerical readout and meters on your DAT machine are almost surely LED's. LED's do not always produce visible light. Infrared LED's are used in wireless remote control devices as well as things like wireless headphone systems. |
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| Lobe |
In acoustics and wireless communications, a lobe pertains to a pattern of transmission (in wireless systems and speakers) or pickup (microphones) that is not spherical, or omnidirectional . Essentially the lobe is the portion of a directional pattern bounded by one or two cones of nulls where there is little or no pickup or transmission. For example, a microphone with a figure 8 pickup pattern has two lobes in its pattern, one on each side of the mic. A hypercardioid mic also has two lobes, it's just that the front (desired) one is much more pronounced than the rear. A cardioid mic generally has one big lobe. As soon as you concentrate the energy of any transmission in a particular direction you create one or more lobes by definition. Wireless systems that use directional antennas also have this type of lobing, and so do loudspeaker systems. The characteristics of most lobes will vary by the wavelength of the sound or electromagnetic energy being radiated. |
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| Phase Locked Loop |
A phase-locked loop (PLL) is an electronic circuit with an oscillator in which the frequency is constantly adjusted to match in phase (and thus lock on) the frequency of an input signal. PLLs are often used to stabilize a particular communications channel (keeping it set to a particular frequency). A PLL can be used to generate a signal, modulate or demodulate a signal (as in FM ), reconstitute a signal with less noise, or multiply or divide a frequency. PLLs are frequently used in wireless communication, particularly where signals are carried using frequency modulation (FM) or phase modulation (PM). PLLs generally take some (small) amount of time to adjust to changes in the input signal so if the circuit is designed accordingly they can also act as a sort of buffer or stabilizer for an input signal with a lot of irregularities. Think of it as a sort of frequency flywheel. |
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| Pole |
This word has a number of mathematical definitions, some of which relate to audio, and particularly the design and implementation of filter s in audio. Capacitors and/or inductors are often integral components of ( analog ) filter design due to the way in which they interact with varying frequencies of periodic energy. For example, it is possible to create a low pass or high pass filter by placing a single capacitor in a circuit, assuming there is some resistance (a load ) elsewhere in the circuit. This is known as an RC circuit (Resistance and Capacitance). In filter design it is understood that a single RC circuit - a circuit with one capacitor and one resistor - is a one "pole" filter. A two pole filter has two RC circuits, and so on. A one pole filter will generally provide a high or low pass roll off in the neighborhood of 6 dB per octave (accompanied by some phase shift). For example, in a high pass filter the voltage of the signal will be cut in half each time the frequency is reduced by an octave, which corresponds to a reduction of 6 dB according to the formula 20log (V1/V2). A two pole filter will have a steeper roll off of 12 dB per octave. The more poles in a filter the steeper the roll off. In a band pass filter more poles equates to a higher Q. If one were to create a resonant filter, as is common in synthesizers (and wireless communication systems (radio, TV, etc.)), more poles would equate to a higher degree of resonance around a more narrow range of frequencies. All of these concepts are clearly related, but applied in different ways. Digital circuits and software can emulate the behavior of poles through certain types of algorithm s; however, software can also be written which will mathematically reduce the amplitude of frequency ranges in a manner quite different from "conventional" filters, which can allow for more control over certain aspects of a complex signal and produce a different sonic characteristic. |
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| Repeater |
A device that amplifies or refreshes a stream of data transmitted over a network so it can travel to more remote receivers. Without a repeater, transmissions will deteriorate as they travel farther and farther from the source, which can ultimately render them unusable. Repeaters come in many different forms depending upon their intended use. For example, wireless communication systems such as cell phones are aided by repeater stations that retransmit signals to broaden a given coverage area. In a fiber optic system a repeater would consist of a photocell, an amplifier, and an LED to retransmit the data. Often times in digital systems the signal is read and then regenerated again. The reason for this is that if a signal is only amplified certain types of degradations such as noise and distortion are also amplified. A digital signal can be read and then generated as if it's a new, clean signal again. Many synchronizers have a Jam Sync feature in which they essentially act as a repeater. |
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| Squelch |
A function found on some radio receiving systems such as wireless microphones and guitar units that allow the user to set the receiver to mute or gate itself when the carrier falls below a specified level. The idea is to eliminate the unwanted noise associated with a radio receiver being tuned between stations, or not properly picking up a station/transmitter to which it is tuned. Typically turning the squelch control "up" makes the receiver have more of a tendency to mute, which means the carrier strength has to be higher in order for it to operate. If the squelch is set too high the audio will mute from time to time, however, if it is set too low you run the risk of getting blasts of noise through the system when the signal strength is compromised for one reason or another. The squelch control was an important part of wireless systems for many years, but with modern technology there are more sophisticated and automated methods of handling these things, which have all but eliminated the manual squelch control from systems. |
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| Stage Monitor |
A speaker that is typically placed within and pointed at the performance area to aid in a performer being able to hear critical elements for performance. Where a PA speaker is designed to provide sound reinforcement intended for the audience, stage monitors are designed in principle to provide sound reinforcement intended for the performers on stage. Stage monitors come in many shapes, styles and forms. Perhaps the most common is the stage wedge, which gets its name from its shape. Stage wedges tend to sit on the floor and the speaker itself is then set at an angle pointing up toward the performers on stage (some are designed with a 30 degree angle, for instance). Some bands prefer to have a separate stage wedge for each member where other bands prefer a general wash of sound provided by a few stage wedges across the front of the stage. Side fill, another application of stage monitors, is intended to perform as its name would incline in that they are typically placed to the side of the stage and are intended to "fill" the stage with sound. Side Fill stage monitors might be an active or passive PA speaker on a stand, stage wedges placed on the floor or on a table, or even studio reference monitors on stands. Just about anything can, and has been used for this application. In-Ear monitors are ear-bud style earphones that are fed their signal by use of a wired or wireless transmission. Similarly speaking, many drummers have been known to use closed headphones on stage for monitors, but usually when they are playing to a click track of some sort. |
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| TNC |
Abbreviation for Threaded Navy Connector. The TNC is a common connector for coaxial cable , particularly in demanding applications. Essentially it can be thought of as a threaded version of a BNC , but because it is threaded most people believe it is capable of a more robust and secure connection than the twist on coupling of BNC connectors. The higher the frequency passing through the connector, the more critical the connection. Many wireless systems utilize TNC connectors for their antenna inputs. |
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| Transmission Loss |
The power that is lost in transmitting a signal from one point to another. In wireless technology, for example, transmission loss can occur when a signal passes through walls, ceilings, etc. Or it can simply occur over (and due to) distance. Wires also have transmission loss due to resistance ,inductance and capacitance . Transmission loss can add up significantly over long distances so many times special equipment is required (such as repeaters , for one example) to maintain the desired integrity of the signal. |
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| True Diversity |
A wireless microphone term. A more advanced form of a diversity receiver , a true diversity system contains a radio receiver that actually has two independent receiver sections, each with its own antenna (rather than a single receiver with one or two antennas), to pick up the transmission from a wireless microphone. The antennas are spaced apart on the unit, and by means of a comparison circuit the unit constantly polls the two receivers to select the one with the strongest signal. The result is an exceptionally stable signal, since the appearance of a dropout in both antennas at the same time is not likely under normal circumstances. |
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| Ultra High Frequency |
Abbreviation for Ultra High Frequency. Similar to VHF , UHF pertains to a band or range of radio frequencies defined by the FCC (Federal Communications Commission) to be used for some television stations and a wide variety of wireless two-way communication systems. UHF picks up where VHF leaves off, having a frequency range of between 300 M Hz and 3000 MHz. |
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| Very High Frequency |
Abbreviation for Very High Frequency . VHF pertains to a band or range of radio frequencies defined by the FCC (Federal Communications Commission) to be used for some television stations and a wide variety of wireless two-way communication systems. The frequency range of VHS is between 30 M Hz and 300 MHz. |
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| Wireless |
A system that is able to transmit data from one point to another without a direct connection, i.e. wires. Typically such systems use some form of RF (Radio Frequency) transmission, which involves modulating the signal with a transmitter and subsequently demodulating it at a receiver tuned to a common frequency. In some situations referring to such systems as wireless can be a bit of a misnomer. For example, in a typical guitar wireless system there are actually two wires where normally only one is required. The cable that would run between a guitar and amp is replaced by a wire from the guitar to a radio transmitter and then another wire from the receiver to the amp. Nevertheless the convenience provided by wireless systems is well known and as technology continues to improve they will likely be used more, and in more creative ways. |
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| Wireless Receiver |
A wireless system consists of two main components: a transmitter, and a receiver. The responsibility of the wireless receiver is to pick up the radio signal broadcast by the transmitter and change it back into an audio signal. Wireless receivers are available in two different configurations. Single antenna receivers utilize one receiving antenna and one tuner, similar to an FM radio. Diversity receivers, or dual antenna systems, often provide better wireless microphone performance. A diversity receiver utilizes two separate antennas spaced a short distance apart and (usually) two separate tuners. An "intelligent" circuit in the receiver automatically selects the better of the two signals, or in some cases a blend of both. Since one of the antennas will almost certainly be receiving a clean signal at any given moment, the chances of a dropout occurring are reduced. There are actually several distinctions among dual antenna systems (diversity, true diversity, etc.) that are variations on the same theme. |
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| Wireless Transmitter
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A wireless system consists of two main components: a transmitter, and a receiver. The transmitter handles the conversion of the audio signal into a radio signal and broadcasts it as a radio wave via an antenna. The antenna may stick out from the bottom of the transmitter or it may be concealed inside. The strength of the radio signal is limited by government regulations. The distance that the signal can effectively travel ranges from 100 feet to over 1,000 feet, depending on conditions and quality of signal. Transmitters are available in two basic types. One type, called a "body-pack" or "belt-pack" transmitter, is a small box about the same size as a pack of playing cards (or smaller in some cases). The transmitter clips to the user's belt or may be worn on the body. For instrument applications, a body-pack transmitter is often clipped to a guitar strap or attached directly to an instrument such as a trumpet or saxophone. In the case of a handheld wireless microphone, the transmitter is built into the handle of the microphone, resulting in a wireless mic that is only slightly larger than a standard wired microphone. Usually, a variety of microphone elements or "heads" are available for handheld wireless microphones. All wireless transmitters require a battery (usually a 9-volt alkaline type) to operate.
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