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A sound reinforcement system may be very complex, including hundreds of microphones, complex mixing and Signal Processing systems, tens of thousands of Watts of amplification, and multiple loudspeaker arrays, all overseen by a team of audio engineers and technicians. On the other hand, a sound reinforcement system can be as simple as a small PA System in a Coffeehouse , consisting of a single microphone connected to a self-powered 100-watt loudspeaker system. In both cases, these systems ''reinforce'' sound to make it louder or distribute it to a wider audience.Eargle, John, and Chris Foreman. Audio Engineering for sound reinforcement. Milwaukee: Hal Leonard Corporation, 2002. 167 Audio engineers and other sound industry professionals disagree over whether these audio systems should be called Sound Reinforcement (SR) systems or Public Address (PA) System s. Some audio engineers distinguish between the two terms by technology and capability, while others distinguish by intended use (e.g., SR systems are for live music whereas PA systems are usually for reproduction of speech and recorded music in buildings and institutions). In some regions or markets, the distinction between the two terms is important. The terms are also considered interchangeable in some areas.Borgerson, Bruce. "Is it P.A. or SR?." Sound & Video Contractor. 1 Nov. 2003. Prism Business Media. 18 Feb. 2007 BASIC CONCEPT A typical sound reinforcement system consists of three parts: input Transducer s such as microphones, which convert sound energy into an audio signal; '''signal Processors ''' such as equalizers and amplifiers, which alter the audio signal characteristics; and '''output transducers''' such as loudspeakers, which convert the audio signal into sound for an audience. Sound is taken and converted into electronic signal by an input transducer (such as a Microphone or a Pickup ) on an Electric Guitar or Electric Bass . A signal processor (such as a Mixing Console , Amplifier , a Reverb effect, or other devices) then alters the signal's equalization, balance, effects and amplitude. Finally, an output transducer such as a Loudspeaker (or, for audio engineers, a set of Headphones ) converts the electronic signal back into sound, so that the listener can hear the end product. This basic concept of sound reinforcement systems encompasses anything from a simple system with only one microphone, amplifier and loudspeaker, to the complex systems in professional applications including multiple mixing boards, monitors and a vast selection of effects. There is debate on the classification of sound systems as "sound reinforcement systems" and "public address systems" depending on size and application. For some sound engineers , a "Sound Reinforcement System" is a system where the audience could hear the speaker or the singer at the microphone without electronic assistance, such as in the case of a Minister addressing a congregation in a church. The components of the SR system amplify or "reinforce" the sound one hears to make it more intelligible. The "PA," or "Public Address System," also known as "commercial paging systems," tend more to be classified as a system where one could not at all hear the person at the microphone without amplification, as in the case of a School Principal addressing all of the classrooms in a school through a PA system. In these PA systems, or distributed sound systems, there are multiple speakers located throughout a business, institution, or large complex. Signal path Sound reinforcement in a large format system typically uses a signal path which starts with the directly-connected instrument or a Microphone (transducer) which is plugged into the Multicore Cable (often called a "snake"). The snake routes the signals of all of the inputs to the Front of the House mixer and to the monitor Console s. Once the signal is in a channel on the console, this signal can be Equalized , Panned and routed to various mix buses. The signal may also be patched into an external effect processor present in the channel (e.g. gate, compressor, reverb). The signal can be routed internally to a summation bus, also known as a mix group, subgroup or simply 'group', to allow the engineer to control the levels of several related signals at once. For example, all of the different microphones for a drum set might be grouped together, so that the volume of the entire drum set sound can be controlled with a single fader. From here each signal is routed through the stereo masters on a console (left and right, or balance, pan, etc.). Additionally, each signal can be sent to separate outputs from the main console, typically referred to as Auxiliary sends, or "Auxes." The next step in the signal path generally depends on the size of the system in place. In smaller systems, the main outputs would be sent to an additional Equalizer , or directly to a Power Amplifier , with one or more loudspeakers (typically two) then connected to that amplifier. In large-format systems, the signal is first routed through an additional Equalizer then to a Crossover . A crossover splits the signal into multiple frequency bands, with each band being sent to separate amplifiers and speaker enclosures for low-, middle-, and high-frequency sounds. Low-frequency sounds are usually sent to Subwoofer s, and middle- and high-frequency sounds are usually sent to full-range Speaker cabinets. SYSTEM COMPONENTS Input transducers Many types of input Transducers can be found in a sound reinforcement system. Microphone s are the most commonly-used input transducers in a sound reinforcement system. They can be classified according to their method of transduction, pickup (or Polar ) pattern or their functional application. Modern microphones either utilize the Electromagnetic principle (dynamic) or the Condenser (capacitor) principle for their method of transduction. Microphone pickup patterns include Omnidirectional (picking sound equally from all directions) or Bidirectional (picking up sound in a figure eight pattern), Cardioid or unidirectional, Hypercardioid and Supercardioid . For a full discussion on pickup patterns, see the article on Microphones . Stand-mounted microphones are the most common in all sound reinforcement applications. Most microphones come with their own stand mount, including studio microphones, which often also have shock-proof and in musical theater. In 1979, Kate Bush became the first performer to use a headworn mic on a large scale concert tour.1 Hanging microphones are commonly used in churches for choirs. Boundary layer microphones are commonly placed on the floor at the front of the stage in theatrical applications, as well as conference rooms and Telecommunications . Distance pickup microphones, such as "shotgun microphones" or "rifle microphones", are used to pick up distant sounds, or in settings where a regular microphone would be obtrusive. Stereo mounts are used to pick up a general coverage of large music ensembles or for picking up the audience ambience for mixing into recordings or blending into artist's IEM s. Instrument-mounted microphones are used on many instruments such as drums, stand-up basses and Acoustic Guitars . Microphones' electrical characteristics include microphone sensitivity; Frequency Response and directional data; Detailed polar curves; Dynamic Range ; Signal Padding ; and Microphone output Impedance . There are different phenomena in the operating environments of sound reinforcement for microphones. Proximity Effect is the change in Frequency Response in relation to the distance between the microphone and the sound source. Since directional microphones are susceptible to the Proximity Effect , Windscreens are necessary to prevent the "p" and "b" sounds from popping when the microphone is near a singer or speaker. Another phenomenon is the microphone picking up reflected sound waves from nearby surfaces. This is commonly observed with podium mounted microphones, where the microphone picks up the original source as well as the reflection off of the podium. This can be remedied by moving the microphone closer to the reflecting surface or by using a more directional microphone. Another phenomenon is multi-microphone interference, which produces a delay effect. This can be avoided by either using directional microphones or keeping the different microphones closer together. Contact Microphone s convert Sound Waves in dense mediums such as wood or metal into an electronic audio signal. They are not often thought of as microphones because of their different application. Contact pickups are often Piezoelectric , and are typically used on stringed instruments, grand pianos and occasionally on drums as Noise Gate triggers. They are usually of the Crystal type, but occasionally are capacitive. Wireless Microphone s use transmitters that are either handheld or bodypacks. Handheld transmitters combine both the microphone diaphragm, preamp and transmitter in one unit. Using wireless microphones can be quite complicated if no Licenses are obtained, especially in a Metropolitan area where many frequency ranges are in use. There are many other types of input transducers which may be used occasionally, including magnetic pickups used in electric guitars and electric basses and Phonograph pickups (cartridges) used in record players. Signal processors Mixing consoles Mixing Console s are the heart of a sound reinforcement system. This is where the operator can mix, equalize and add effects to sound sources. Many different features are included on top of the basic mixing function in different mixing consoles. The most standard features are onboard Equalization and preamplificaiton, audio inserts and auxiliary outputs. More advanced mixing consoles include metering, mute groups, voltage controlled amplifiers (VCA), VCA groups, LCR panning, Scenes and Matrix output. Multiple consoles can be used for different applications in a single sound reinforcement systems. There are other types of consoles than a sound reinforcement mixing console. Besides non-SR consoles (such as those for recording, Broadcast or Post Production ), there is the stage monitor mixing console, which is dedicated to creating mixes for the monitors on stage. Subsequently these consoles have a large number of mix group controls. Thus each musician on stage can have a different mix of their own, (e.g. the lead singer has her voice louder in her monitor loudspeaker and the keyboardists has his Keyboard louder in his monitor loudspeaker). These consoles are normally placed at the side of the stage so that the operator can be in direct communication with the performers on stage. Some mixers have amplifiers built in, which are called powered mixers. Though these are easy to set up, they are not as versatile and limit the operator to certain loudspeakers or speaker configurations. In sound reinforcement, the mixing console must be located where the operator can see and hear the action on stage. This means the console will be ideally placed within or behind the audience. Some venues with permanent systems installed (e.g. religious facilities and theaters) place the mixing console within an enclosed booth, but this approach is more appropriate for broadcast and recording applications. In sound reinforcement, mixing from within a booth is undesirable as it prevents the operator from hearing the combined effect of the artist, the loudspeakers, the audience, the mix and the acoustics of the room. Digital Mixing Console s are more versatile and offer many new features, such as the ability to save multiple mute groups, multiple VCA groups and channel settings into a scene and reconfigure signal routing. The faders can be "swapped" or "flipped" to show aux send levels; a feature very useful in mixing artist's monitors. In addition, digital consoles often include a range of special effects such as compression, reverb, and digital delay. Many digital mixing consoles are designed to operate as a remote control to a DSP engine. With digital consoles it is also possible to use a computer as a remote control, yet this is not very popular with operators who are used to analog systems and would like instant access to all controls, a function which a keyboard cannot keep up with let alone a mouse. Digital Signal Processing can perform automatic mixing for some simple applications, such as courtrooms, conferences and panel discussions, but at this time no digital mixer in live audio includes automixing. Equalizers have knobs which adjust three parameters: frequency, boost/cut and Q (bandwidth). These equalizers are often found built into each channel in mixing consoles, but are also available as separate units. Parametric equalizers first became popular in the 1970s and have remained the program equalizer of choice since then. Graphic equalizers have faders which resemble a frequency response curve plotted on a graph. Sound reinforcement systems normally use graphic equalizers designed on one-third Octave centers. End-cut Filters restrict a given channels Bandwidth extremes, which can prevent subsonic disturbances and RF or lighting control disturbances from interfering with the audio system. End-cut filter sections are often included with graphic equalizers to give full control of the frequency range. If their response is steep enough, then High-pass Filter s (low-cut) and Low-pass Filter s (high-cut) can function as end-cut filters. A feedback suppressor is a specialized type of filter which automatically detects and suppresses Feedback by cutting a deep notch on the frequency which is feeding back. Compressors and limiters Compressors And Limiters are used to maintain an average signal level by automatically reducing the level of louder sound. Signal Compression is necessary because the Dynamic Range of equipment may be smaller than that of the signal and cause distortion, clipping, or even equipment damage. When the signal is compressed, there is a smaller difference between the volume of the loudest and quietest sounds. Thus the content can still sound like it's louder or quieter but actually have pretty much the same volume. The output level of a compressor can then be turned up to optimize the efficient use of a systems dynamic range. Compressors also have Attack and Release settings, which determine how long the compressor will wait before turning down the volume on a loud sound, and how long to wait before turning the volume up again. Attack time is usually within the range of Microseconds , while release time is in the range of seconds. There is also a Threshold setting which determines at what minimum sound pressure level the compressor should start compressing. Compressors are useful for restricting the volume of vocalists with a large dynamic range. Vocalists using microphones need to learn how to distance their mouth from the microphone when singing especially loud notes, such as high notes. Compressors provide for safer signal handing by avoiding distorting and clipping and also a more pleasant listening experience. A limiter is essentially a compressor with the most extreme setting in effect, and sets a sound level ceiling on a signal instead of a slow curve. These are extremely valuable for suppressing very loud pops (such as when unplugging a guitar or dropping a microphone) which could damage the audio system. Noise gate A Noise Gate sets a threshold where if it is any quieter it will not let the signal pass and if it is louder it "opens the gate." Thus the noise gate's functions are very much opposite to those of a compressor. There are also attack and release settings, which work in the same way as a compressor. Noise gates are useful for microphones which will pick up noise which is not relevant to the program, such as the hum of a miked electric guitar amplifier or the rustling of papers on a Minister's podium. Noise gates are also used with the microphones placed near the different drums and cymbals in the drum kits in many hard rock and metal bands. Without a noise gate, the microphone for a specific instrument, such as the floor tom, will also pick up sounds from nearby drums or cymbals, which bleed into its microphone. With a noise gate, the threshold of sensitivity for each microphone for each instrument from the drum kit can be set so that only the direct striking of the instrument will be picked up by the microphone, and not the nearby sounds. Other effects and accessories Reverberation and Delay (audio Effect) effects are widely used in sound reinforcement systems to give the effect of natural reverb. Less commonly, modulation effects such as Flanging and Phaser (effect) s are applied to some instruments for an unusual sound effect. The Exciter (effect) "livens up" the sound of audio signals by applying dynamic equalization, phase manipulation and harmonic synthesis of (usually) high frequency signals. A wide range of accessories are used in sound reinforcement systems. High-end Audio Cables are shielded to prevent hum and interference. Rack-mount cases, such as the industry standard 19-inch Rack s are used to store and transport effects units and amplifiers. Some racks have cushioned shock-mounting to protect equipment from impacts. Amplifiers Amplifiers increase the signal level to drive the loudspeaker. All output transducers require amplification of the signal by amplifiers, including loudspeakers, monitor speakers, and even headphones. The heavy-duty amplifiers used to power loudspeakers and monitor speakers are referred to as power amplifiers. Most professional amplifiers are self-protected from overdriven ("clipped") signals, short circuits across the output, or thermal overload. Compression and limiting features are often used to protect loudspeakers and amplifiers from signal overload. Like most sound reinforcement equipment, professional amplifiers are designed to be mounted on 19-inch Rack s. Many power amplifiers have internal fans to draw air across the heat sinks. Heat dissipation is an important factor for operators to consider when mounting amplifiers onto equipment racks, since they can generate a significant amount of heat; if amplifiers are placed in a rack that is against a wall, or if the Ambient air temperature is too hot, the amplifiers may overheat. Another factor affecting the heat dissipation is the presence of dust. If the grilles of an amplifier's fan intake become clogged with dust, the amplifier may not be able to stay cool enough. Amplifiers often have several different input connectors, such as 3-pin XLR's and 1/4 inch TRS ("tip-ring-sleeve" or "stereo") jacks. Output connections have varied a great deal in the past, ranging from 1/4-inch jacks,post (or "banana") terminals, occasionally 3-pin XLR connectors, and in the 1990s Neutrik "Speakon" locking connectors. Amplifier switches include a level control, a mono-stereo switch, a bridge switch (which has the internal wiring reversed to correct phase problems), a limiter switch (to prevent speaker-destroying amplifier distortion); a ground lift switch (to reduce hum); a "clip" or "overload" LED to indicate that the amplifier is approaching distortion; and warning lights (e.g., "Protect", "Temp." or "Fault" LEDs) to indicate output problems, short circuits, or overheating. Amplifiers have breakers or fuses, and in the case of older amplifiers, a speaker output fuse. Digital loudspeaker system controllers (DLSC), also known as digital crossover networks, are most commonly used to process the final mix being sent from the mixing console to the amplifiers, and in turn to the loudspeakers. Multiple loudspeakers with a more narrow-band response, tailored to specific frequency bands, can be used together (i.e. lows, mids and highs) to obtain a more accurate reproduction of the input signal. This also makes more efficient use of amplifier power by sending each amplifier only the frequency band that its respective loudspeaker can reproduce. The crossover function of a DLSC does this splitting of the input signal into separate outputs for each speaker.Most DLSCs have calibration and testing functions, such as a tone generator, a Pink Noise generator coupled with a Real-time Analyzer and automated room optimization. Output transducers Loudspeakers Loudspeaker s (also known as drivers) are the main speakers which project the sound to the Audience . A basic, inexpensive PA speaker may only have a single full-range loudspeaker system. Professional PA speakers usually have different drivers that provide the low-, middle-, and high Frequency sounds. In the 1960s, most PA spakers were "columns" with several speakers mounted in a tall cabinet, which evolved into cube-shaped speakers mounted on stands by the end of the decade. In the 1970s, PA speakers developed into stacks of "bass bin"s and high-range horns. By the 1980s, PA speakers became easier to use and set up, because they increasingly contained a range of different drivers (woofer and horn) with built-in crossovers. In the 1990s and 2000s, professional PA speakers were often "actively controlled" with electronic Processors that automatically adjust crossover and Equalization settings and protect the speakers. In the 2000s, PA speaker cabinets were increasingly built with protection circuitry that protects high and mid frequency drivers from accidental exposure to low frequency sound material. Some PA speakers also protect the high frequency drivers with "current-to-light" conversion circuitry, which takes excess current which would otherwise damage a horn, and uses it to light a small light bulb. Another circuit protection technique used to protect horns is current sensing / self-resetting breakers, which protects the horn in cases of high-volume feedback (e.g., a microphone being accidentally dropped into a monitor). As well, many PA speaker companies have begun providing Neutrik Speakon multi-pin connectors, instead of the decades-old 1/4" jacks. The Speakon connectors provide a much larger metal contact area for high current PA applications. The four different types of , Magnet , cone or Diaphragm , and a frame or structure. PA speakers have a power rating (in Watts ) which indicates their maximum power capacity, to help users avoid overloading them with excessively powerful amplifiers. However, even an amplifier with less power output than a speaker's power rating can destroy the speakers if the amplifier signal becomes heavily Distorted , especially if the distortion is from low-range sounds. The power rating of speakers is expressed either as RMS ( Root Mean Square ) or PGM (Program). The PGM rating became more widely used in the 2000s; it means "do not use more than the indicated power with this speaker." Trapezoidal or "wedge-shaped" speakers have a shape which allows the speakers to be grouped into arrays so that they can be mounted on rigging. Professional PA speakers are usually designed with internal brace "flying" hardware (e.g., steel eyebolts) for safe suspension of speakers from rigging or ceilings. Many speakers are designed with interlocking corners so that they can be vertically or horizontally stacked for large concerts. Large, heavy PA speakers are often equipped with wheeled dollys, to facilitate on-stage placement. Monitors =Speakers Monitor Speakers are usually full-range speakers which are directed towards an individual performer, a sound operator or entire sections of a stage. Most monitor speaker cabinets have a wedge shape, so that they will point up towards the performer when they are placed on their sides on the stage. Monitor speaker cabinets usually contain a speaker (driver) for low- and mid-frequency sounds and a horn for high-frequency sounds. Most monitor speakers include an L-pad for controlling the volume of the horn. In the 2000s, PA speaker companies began offering a range of powered monitor speakers, which contain a power amplifier. Another trend of the 2000s was the blurring of the lines between monitor speaker cabinets and regular speaker cabinets; many companies began selling wedge-shaped full-range speakers which they state can be used for monitors or regular Front of House purposes. =Headphones Headphones are typically used by the sound board operator to monitor specific channels or to listen to the entire mix. Some performers may use headphones as monitors as well, such as drummers in pop music bands. In the 2000s, some bands and singers have begun using small "in ear"-style headphone monitors. In-ear monitors allow musicians to hear their voice and the other instruments with a clearer, more intelligible sound, because the molded in-ear headphone design blocks out on-stage noise. While some in-ear monitors are "universal fit" designs, some companies also sell custom-made in-ear monitors, which require a fitting by an Audiologist . Custom-made in-ear monitors provide an exact fit for a performer's ear. APPLICATIONS Sound reinforcement systems are used in a broad range of different settings, each of which poses different challenges. Church sound Designing systems in churches and similar religious facilities often poses a challenge, because the speakers have to be unobtrusive to blend in with antique woodwork and stonework. In some cases, audio designers have designed custom-painted speaker cabinets so that the speakers will blend in with the church architecture. Some church facilities, such as Sanctuaries or chapels are long rooms with low ceilings, which means that additional fill-in speakers are needed throughout the room to give good coverage. An additional challenge with church SR systems is that, once installed, they are often operated by amateur volunteers from the congregation, which means that they must be easy to run and troubleshoot. Touring systems Touring sound systems have to be easy to set up, and they need to use "field-replaceable" components such as speakers, horns, and fuses, which are easily accessible for repairs during a tour. Tour sound systems are often designed with substantial redundancy features, so that in the event of equipment failure or amplifier overheating, the system will continue to function. Weekend band PA systems are a niche market for touring SR gear. Weekend bands need systems that are small enough to fit into a minivan or a car trunk, and yet powerful enough to give adequate and even sound dispersion and vocal intelligibility in a noisy club or bar. As well, the systems need to be easy and quick to set up. Sound reinforcement companies have responded to this demand by offering equipment that fulfills multiple roles, such as "amp-mixers" (a mixer with an integrated power amplifier and effects) and powered subwoofers (a subwoofer with an integrated power amplifier and crossover). These products minimize the amount of wiring connections that bands have to make to set up the system. Some subwoofers have speaker mounts built into the top, so that they can double as a base for the stand-mounted full-range PA speaker cabinets. Sports sound systems Systems for outdoor sports facilities and ice rinks often have to deal with substantial echo, which can make speech unintelligible. Sports and recreational sound systems often face environmental challenges as well, such as the need for weather-proof outdoor speakers in outdoor stadiums and Humidity - and spash-resistant speakers in swimming pools. Live theater Sound for live theaters, opera theaters, and other dramatic applications may pose problems similar to those of churches, in cases where a theater is an old heritage building; speakers and wiring may have to blend in with woodwork. As well, the need for clear sight lines in some theaters may make the use of regular speakers unacceptable; instead, slim, low-profile speakers may be needed. In live theater and drama, performers move around onstage, which means that Wireless microphones may have to be used. Wireless microphones need to be set up and maintained properly, to avoid interference and reception problems. Lecture halls and conference rooms Lecture halls and conference rooms pose the challenge of reproducing speech clearly to a large hall, which may have reflective, Echo -producing surfaces. In some conferences, sound engineers have to provide microphones for a large number of people, in the case of a panel conference or debate. In some cases, automatic mixers are used to control the levels of the microphones. Rental systems Audio visual (AV) rental systems have to be able to withstand heavy use, and even abuse from renters. For this reason, rental companies tend to own speaker cabinets which are heavily braced and protected with steel corners, and electronic equipment such as power amplifiers or effects are often mounted into protective road cases. As well, rental companies tend to select gear which has electronic protection features, such as speaker-protection circuitry and amplifier limiters. As well, rental systems need to be easy to use and set up, and they must be easy to repair and maintain for the renting company. From this perspective, speaker cabinets need to have easy-to-access horns, speakers, and crossover circuitry, so that repairs or replacements can be made. Since rental gear is often used by fairly inexperienced users, rental companies often rent powered amplifier-mixers, mixers with onboard effects, and powered subwoofers, which are easier to set up and use. Live music clubs Setting up sound reinforcement for live music clubs often poses unique challenges, because there is such a large variety of venues which are used as clubs, ranging from former Warehouses or music theaters to small restaurants or basement pubs with concrete walls. In some cases, clubs are housed in multi-story venues with balconies, which makes it hard to get a consistent sound for all audience members. The solution is to use fill-in speakers to obtain good coverage, using a delay to ensure that the audience does not hear the same sound at different times. Another problem with designing sound systems for live music clubs is that the sound system may need to be used for both prerecorded music played by DJ s and live music. If the sound system is optimized for prerecorded DJ music, then it will not provide the appropriate sound qualities needed for live music, and vice versa. Lastly, live music clubs can be a hostile environment for sound gear, in that the air may be hot, humid, and smoky; in some clubs, keeping amplifiers cool may be a challenge. SETTING UP AND TESTING Large-scale sound reinforcement systems are designed, installed, and operated by audio engineers and audio technicians. During the design phase of a newly constructed venue, audio engineers work with architects and contractors, to ensure that the proposed design will accommodate the speakers and provide an appropriate space for sound technicians and the racks of audio equipment. During the design phase of a venue, sound engineers provide advice on which audio components would best suit the space and its intended use, and on the correct placement and installation of these components. During the installation phase, sound engineers ensure that high-power electrical components are safely installed and connected and that ceiling- or wall-hung speakers are properly mounted (or "flown") onto Rigging . When the sound reinforcement components are installed, the sound engineers test and calibrate the system, so that its sound production will suit the acoustic environment of the venue. System testing A sound reinforcement system should be able to accurately reproduce a signal from its input, through any processing, to its output, without any coloration or distortion. However, due to inconsistencies in venue sizes, shapes, building materials, and even crowd densities, this is not always possible without prior calibration of the system. This can be done in one of several ways: The oldest method of system Calibration involves a set of healthy ears, test program material (i.e. music or speech), a graphic equalizer, and last but certainly not least, a familiarity with the proper (or desired) frequency response. One must then listen to the program material through the system, take note of any noticeable frequency changes or resonances, and subtly correct them using the equalizer. However, simply relying on a prior knowledge of how the program material "should" sound can be very subjective, and should be avoided if at all possible. |
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