42V PowerNet The official name for the 42 V automotive electrical power system. The value of 42 volts comes from a tripling of the normal 12 V car battery to 36 volts which measures 42 volts when running.
5.1 surround sound The digital audio multichannel format developed by the Moving Picture Experts Group (see MPEG) for digital soundtrack encoding for film, laserdiscs, videotapes, DVD, and HDTV broadcast. The designation "5.1" (first proposed by Tom Holman of THX fame) refers to the five discrete, full bandwidth (20-20 kHz) channels -- left, right, & center fronts, plus left & right surrounds -- and the ".1" usually refers to the limited bandwidth (20-120 Hz) subwoofer channel, but can also refer to a special effects/feature channel. Terminology used by both Dolby Digital and DTS Consumer (the home version of their theater Coherent Acoustics system).
facetious One of the words that contain all five vowels in the correct order. Other examples are obscure scientific terms.
fader A control used to fade out one input source and fade in another. The fading of a single source is called attenuation and uses an attenuator.
fadista A singer of tradition Portuguese musical style of fado (see next entry).
Fahnestock clip Electronics. A type of spring-clip terminal for electrical wire that is one of the oldest and most popular ever made.
Fahrenheit Abbr. F Of or relating to a temperature scale that registers the freezing point of water as 32 °F and the boiling point as 212 °F, under normal atmospheric pressure. [AHD] (In scientific and technical contexts temperatures are now usually measured in degrees Celsius rather than Fahrenheit.) [After Gabriel Daniel Fahrenheit.]
Fahrenheit, Gabriel Daniel (1686-1736) German-born physicist who invented the mercury thermometer (1714) and devised the Fahrenheit temperature scale. [AHD]
Fairchild 670 Compressor Limiter designed by Rein Narma in 1959, while at Fairchild Recording Equipment Company in Long Island City, NY. The most revered pro audio compressor.
fall time Electronics.The time required for a signal to decay from 90 % to 10 % of its maximum amplitude.
fandango Music. An animated Spanish or Spanish-American dance in triple time.
FAQ (frequently asked question) Acronym commonly seen on bulletin boards, Internet Web sites, and corporate information centers. By compiling FAQ lists (FAQs), organizations significantly reduce time spent repeatedly answering the same questions.
farad Abbr. F The unit of capacitance in the meter-kilogram-second system equal to the capacitance of a capacitor having an equal and opposite charge of 1 coulomb on each plate and a potential difference of 1 volt between the plates. [AHD] [After Michael Faraday.]
Faraday, Michael (1791-1867) British physicist and chemist who discovered electromagnetic induction (1831) and proposed the field theory later developed by Maxwell and Einstein. [AHD] After announcing that a new source of energy was possible by moving a magnet in a coil of wire, many declared him a fraud. Faraday responded with his memorable words: "Nothing is too wonderful to be true, if it be consistent with the laws of nature." See Faraday's Magnetic Field Induction Experiment.
Faraday Effect See: Kerr Effect.
far-end Teleconferencing term meaning the distant location of transmission; the other end of the telephone line, as opposed to your end (known as the near-end).
far-end crosstalk Crosstalk that is propagated in a disturbed channel in the same direction as the propagation of the signal in the disturbing channel. The terminals of the disturbed channel, at which the far-end crosstalk is present, and the energized terminals of the disturbing channel, are usually remote from each other.
far-field or far sound field The sound field distant enough from the sound source so the SPL decreases by 6 dB for each doubling of the distance from the source (inverse square law). Contrast with near-field.
Fast Ethernet See: Ethernet.
fax on demand One of the terms for the process of ordering fax documents from remote machines via telephone, using a combination of voice processing and fax technologies. Also called fax-back.
fax-back See fax on demand.
FDTD (finite difference time domain) Mathematics. A numerical technique for solving a partial differential equation involving time and space variables. The solution is implemented sequentially in the time domain. [IEEE] Considered easy to understand and easy to implement in software it is a popular technique.
FEA See Finite Element Analysis.
feedback Acoustics. See acoustic feedback.
feedback Electronics. The return of a portion of the output of a process or system to the input, especially when used to maintain performance or to control a system or process. [AHD]
feedback The longest word in the English language that uses all the letters "A" through "F." [Thanks, Brad, for being so observant while playing Trivial Pursuit®.]
Feedback Stability Margin See: FSM
feedback suppressor An audio signal processing device that uses automatic detection to determine acoustic feedback frequencies and then positions notch filters to cancel the offending frequencies. Other methods use continuous frequency shifting (a very small amount) to prevent frequency build up and feedback before it happens.
feedback troxelator Faster than an exterminator. More powerful than an eliminator. Able to leap over an obliterator in a single sample -- 'Look; up in the sky;' 'It's a bird;' 'It's a plane;' 'It's The Troxelator ...,' Rane's patented feedback suppressor technology developed by and named after Dana Troxel, one of their senior design engineers, who proclaims: "I AM THE TROXELATOR."
feed-through hole See vias.
femto- Prefix for one thousandth of one trillionth (10-15), abbreviated f.
Fender, Clarence Leonidas "Leo" (1909-1991) American inventor and entrepreneur who founded the Fender Electric Instrument Company in 1946 and invented the legendary Stratocaster and Telecaster guitars.
Fender-Rhodes Musical Instrument. Nickname for the Rhodes electro-mechanical piano as manufactured by Fender, invented by Harold Rhodes in the '50s.
ferrite 1. Any of a group of nonmetallic, ceramic-like, usually ferromagnetic compounds of ferric oxide with other oxides, especially such a compound characterized by extremely high electrical resistivity and used in computer memory elements, permanent magnets, and various solid-state devices. 2. Iron that has not combined with carbon, occurring commonly in steel, cast iron, and pig iron below 910°C. [AHD]
ferrite bead Electronic component. A small toroidal shaped part made from a mixture of iron, nickel and zinc oxides used to suppress EMI in audio and other electronic equipment. Usually seen on the inputs and outputs of equipment, ferrite beads act electrically like an inductor in series with a resistor. For more details see "The Use of Ferrites in EMI Suppression" by Steward, now owned by Laird.
Festival No. 6 A unique music festival held in Portmeirion, Wales, a picturesque village on the north coast, most famously used as "The Village" in the acclaimed 1960s television series, "The Prisoner," which starred Patrick McGoohan whose character was known as "Number 6" --hence the name of the festival.
FET (field-effect transistor) A three-terminal transistor device where the output current flowing between the source and drain terminals is controlled by a variable electric field applied to the gate terminal. The gate design determines the type of FET: either JFET (junction FET) or MOSFET (metal-oxide semiconductor FET). Each type has two polarities: positive, or p-channel devices, and negative, or n-channel devices. In a JFET device the gate forms a true semiconductor junction with the channel, while in a MOSFET device the gate is insulated from the channel by a very thin (typically less than the wavelength of light) layer of glass (silicon dioxide) and the gate is either metal or doped silicon (polysilicon), hence the acronym metal-oxide semiconductor.
Fête de la Musique (aka World Music Day) Music festival begun in 1982 in Paris that is now celebrated each year in cities located in over 100 countries, all on the same day, June 21.
FFT (fast Fourier transform) 1. Similar to a discrete Fourier transform except the algorithm requires the number of sampled points be a power of two. 2. A DSP algorithm that is the computational equivalent to performing a specific number of discrete Fourier transforms, but by taking advantage of computational symmetries and redundancies, significantly reduces the computational burden. [It is believed Cornelius Lanczos of the Boeing Co. in the 1940's first described the FFT.]
fiber-optic cable microphone Dubbed by the U.K. inventors as the “world’s nervous system,” it is a method based on the Rayleigh scattering effect of fiber-optic cables, using DAS (distributed acoustic sensing) . Hit the links for details.
fiber-optic microphone Microphones. A technology based on sensing changes in light intensity to convert acoustic waves into electrical signals.
fiber optics The technology of using glass fibers to convey light and modulated information. Short distances (typically less than 150 feet) use plastic fibers, while long distances must use glass fibers. See cables.
fiddle Musical Instrument. Popular name for the violin.
Fidelipac (aka NAB cartridge or simply 'cart') Magnetic tape recording format that became the industry standard for radio broadcasting, introduced in 1959,
field Mathematics. A set of elements having two operations, designated addition and multiplication, satisfying the conditions that multiplication is distributive over addition, that the set is a group under addition, and that the elements with the exception of the additive identity form a group under multiplication. [AHD]
fig newton One kilogram of falling figs.
figure-of-eight See: microphone polar response.
filament Vacuum Tubes. The heating element in a vacuum tube. [It's that glowing thing.]
film resistor Electronic Component. A type of made by depositing a thin layer of resistive material on an insulating core. Favored for audio due to their low noise characteristic.
film sound glossary See Larry Blake's Film Sound Glossary; find out what a "binky" is.
filter Any of various electric, electronic, acoustic, or optical devices used to reject signals, vibrations, or radiation of certain frequencies while passing others. Think sieve: pass what you want, reject all else. For audio use the most common electronic filter is a bandpass filter, characterized by three parameters: center frequency, amplitude (or magnitude), and bandwidth. Bandpass filters form the heart of audio graphic equalizers and parametric equalizers.
FinFet (fin field-effect transistor) Solid-state Physics. The term was coined by University of California, Berkeley researchers (Profs. Chenming Hu, Tsu-Jae King-Liu and Jeffrey Bokor) to describe a nonplanar, double-gate transistor built on an SOI substrate. [Huang, X. et al. (1999) "Sub 50-nm FinFET: PMOS" International Electron Devices Meeting Technical Digest, p. 67. December 5–8, 1999]
finite field See: Galois field.
fipple Musical Instruments. 1. A whistle like mouthpiece for certain wind instruments, such as a recorder or flageolet, that channels the breath toward the sounding edge of a side opening. 2. An object similar to a fipple in an organ pipe. [AHD]
FIR (finite impulse-response) filter A commonly used type of digital filter. Digitized samples of the audio signal serve as inputs, and each filtered output is computed from a weighted sum of a finite number of previous inputs. An FIR filter can be designed to have linear phase (i.e., constant time delay, regardless of frequency). FIR filters designed for frequencies much lower that the sample rate and/or with sharp transitions are computationally intensive, with large time delays. Popularly used for adaptive filters.
Firefly See ZigBee.
Firewire See IEEE 1394.
firkytoodle An English word no longer in print (except here) meaning to engage in intimate physical affection, as a prelude to sexual intercourse; foreplay (17th to 19th century).
firmware Computer read-only memory (ROM) code (files) residing inside DSP and microprocessor ICs that controls the hardware response to software instructions -- the liaison between software and hardware. Now really a specific type of software since most firmware updates are done via some sort of streaming network rather than burning new hardware ROMS.
fishpaper An insulating paper, often fiber- or oilcloth-like, used in the construction of transformers and coils. [Historical Note: Alvin G. Sydor writes: "In 1729 Stephen Gray made the discovery of the conducting and non-conducting power of different substances. Gray found that by using woven silk served as an excellent insulator. Some years later it was found that the paper industry could provide what was equivalent to woven silk. Later it was discovered that if the paper was saturated with fish oil its ability as an insulator was much improved particularly when used in harsh environments and high voltages."]
fixed-point A computing method where numbers are expressed in the fixed-point representation system, i.e., one where the position of the "decimal point" (technically the radix point) is fixed with respect to one end of the numbers. Integer or fractional data is expressed in a specific number of digits, with a radix point implicitly located at a predetermined position. Fixed-point DSPs support fractional arithmetic. A couple of fixed-point examples with two decimal places are 4.56 and 1789.45.
FLAC (free lossless audio codec) A lossless compression standard for music files.
flanging Originally, "flanging" was achieved using two reel-to-reel tape recorders playing the same program, in synchronization, with their outputs summed together. By alternately slowing one machine, then the other, different phase cancellations occurred in the summation process. The "slowing down" was done simply by pressing against the flanges of the tape reels, hence the original term "reel flanging," soon shortened to just "flanging." Since the two identical signals would alternately add and subtract due to the introduced phase (timing) difference, the audible effect was one of a sweeping comb filter. It was described as a "swishing" or "tunneling" sound. Soon electronic means were devised to mimic true "reel flanging" by using delay lines and mixing techniques. Adding a low-frequency oscillator to modulate the audio delay line's clock signal created a sweeping effect, much like a jet airplane taking off. The best flangers used two delay lines. Compare with phaser
flanking sound transmission Acoustics. The transmission of sound from a source room (i.e., a room in which a source is located) to an adjacent receiving room by paths other than the common partition. [Harris]
Fleming, Sir John Ambrose (1849-1945) British electrical engineer and inventor known for his work on electric lighting, wireless telegraphy, and the telephone. He invented and patented the first tube, a diode (which he called a thermionic valve, he used for signal detection (although Edison technically developed the first tube with a version of his light bulb).
Fletcher, Harvey (1884-1981) American physicist and legendary pioneer in acoustics and hearing most often associated with the Fletcher-Munson Curves below. He published his findings in his book, Speech and Hearing (Van Nostrand Co., 1929). [And H. D. Arnold wrote the introduction.]
Fletcher-Munson Curves In the '30s, researchers Fletcher and Munson first accurately measured and published a set of curves showing the human's ear's sensitivity to pure tone loudness verses frequency ("Loudness, its Definition Measurement and Calculation," J. Acoust. Soc. Am., vol. 5, p 82, Oct. 1933). They conclusively demonstrated that human hearing is extremely dependent upon loudness. The curves show the ear most sensitive to pure tones in the 3 kHz to 4 kHz area. This means sounds above and below 3-4 kHz must be louder in order to be heard just as loud. For this reason, the Fletcher-Munson curves are referred to as "equal loudness contours." They represent a family of curves from "just heard," (0 dB SPL) all the way to "harmfully loud" (130 dB SPL), usually plotted in 10 dB loudness increments.
D. W. Robinson and R. S. Dadson revised the curves in their paper, "A Redetermination of the Equal-Loudness Relations for Pure Tones," Brit. J. Appl. Phys., vol. 7, pp. 156-181, May 1956. These curves supersede the original Fletcher-Munson curves for all modern work with pure tones. Robinson & Dadson curves are the basis for ISO: "Normal Equal-Loudness Level Contours," ISO 226:1987 -- the current standard.
Users of either of these curves must clearly understand that they are valid only for pure tones in a free field, as discussed in the following by Holman & Kampmann. This specifically means they do NOT apply to noise band analysis or diffused random noise for instance, i.e., they have little relevance to the real audio world. A good overview is T. Holman and F. Kampmann, "Loudness Compensation: Use and Abuse," J. Audio Eng. Soc., vol. 26, no. 7/8, pp. 526-536, July/August 1978.
For real audio use, the Steven's curves are more applicable: S. S. Stevens, "Perceived Level of Noise by Mark VII and Decibels (E)," J. Acoust. Soc. Am., vol. 51, pp. 575-601, 1972. [Used to create ISO 532:1975 and ASA S3.4-1980] See Holman & Kampmann above for discussion.
flicker AC Power Systems. The effect caused when load switching creates a short-duration dip in the AC voltage, as when the lights dim momentarily when the refrigerator compressor kicks in.
flicker noise or 1/f noise Noise whose amplitude varies inversely with frequency. Mainly used in solid-state physics to describe noise with 1/f behavior, such as the noise resulting from impurities in the conducting channel, generation and recombination noise due to base current in transistors, etc. Pink noise has a 1/f characteristic so the two terms are often interchanged, however when used to describe semiconductor noise (in op amps for instance) it is uniquely a low-frequency phenomena occurring below 2 kHz, while in audio, pink noise is wideband to 20 kHz.
floating-point A computing method where numbers are expressed in the floating-point representation system, i.e., one where the position of the decimal point does not remain fixed with respect to one end of numerical expressions, but is regularly recalculated. A floating-point number has four parts: sign, mantissa, radix, and exponent. The sign indicates polarity so it is always 1 or -1. The mantissa is a positive number representing the significant digits. The exponent indicates the power of the radix (i.e., the number base, usually binary 2, but sometimes hexadecimal 16). A common example is the "scientific notation" used in all science and mathematics fields. Scientific notation is a floating point system with radix 10 (i.e., decimal). See FLOPS.
floating unbalanced line A quasi-balanced output stage consisting of an unbalanced output connected to the tip of a ¼" TRS (tip-ring-sleeve) jack through an output resistor (typically in the 50-300 ohms range). An equal valued resistor is used to tie the ring terminal to signal ground. The sleeve connection is left open or "floating." Thus, from the receiver's viewpoint, what is "seen" are two lines of equal impedance, used to transfer the signal. In this sense, the line is 'balanced," although only one line is actually being driven. Leaving the sleeve open, guarantees that only one end of the shield (the receiving end) will be grounded. A practice that unbalanced systems often require. For trouble free interconnections, balanced lines are always the preferred choice.
floobydust A contemporary made-up term, one meaning being derived from the archaic Latin miscellaneus, whose disputed history springs from Indo-European roots, probably finding Greek origins (influenced, of course, by Egyptian linguists) -- meaning a mixed bag, or a heterogeneous motley mixed varied assortment. Popularized within the audio community when borrowed and used by the author of this web page as a chapter title in the National Semiconductor Audio Handbook, first published in 1976.
FLOPS (floating-point operations per second) A measure of computing power.
flute Musical Instruments. A high-pitched woodwind instrument consisting of a slender tube closed at one end with keys and finger holes on the side and an opening near the closed end across which the breath is blown. Also called transverse flute. [AHD] The oldest wooden musical instruments discovered to date were found in Greystone, Ireland and date from 4000 BC. And the oldest instrument of any sort is a flute made from bird bones found in Germany dating from 35,000 BC.
flutter 1. Analog Recording. Any significant variation from the designed study rotational speed of a recording or playback mechanism, e.g., turntables and analog tape recorders (typically at 5-10 Hz rate). Heard as rapid fluctuation in pitch when played back. Compare with wow. 2. Telecommunications. Any rapid variation of signal parameters, such as amplitude, phase, and frequency.
flutter echo Acoustics. An acoustic effect in some rooms where sound is reflected back and forth between two parallel surfaces, such as opposite walls. In order to qualify as a flutter echo the reflections must be fewer than about 15 or so per second. This happens when the walls are more than about 25 feet apart. Parallel surfaces closer than this give rise to standing waves that result in nonuniform distribution of sound between the surfaces. [White]
fluxivity Magnetic Recording. The recorded flux per unit track width. See AES7: AES standard for the preservation and restoration of audio recording -- Method of measuring recorded fluxivity of magnetic sound records at medium wavelengths.
flux unit See: jansky.
FM (frequency modulation) Radio broadcast. The encoding of a carrier wave by variation of its frequency in accordance with an input signal. [AHD]
FOH Abbreviation for front of house, used to describe the main mixer usually located in the audience for sound reinforcement systems. Meant to differentiate the main house mixer from the monitor mixer normally located to the side of the stage.
foldback The original term for monitors, or monitor loudspeakers, used by stage musicians to hear themselves and/or the rest of the band. The term "monitors" has replaced "foldback" in common practice.
Foley A term synonymous with film sound effects. A recording studio Foley stage is where the sound effects are generated in synch with the moving picture. Named after Jack Foley, who invented sound effects for film sound while working for Universal. He simultaneously added music and effects to the previously silent film "Showboat" and the first "Foley" session was born.
follower Shortened form for a number of electronic circuit buffer amplifiers named voltage followers, cathode followers, emitter followers, etc.
Fonz Foot Wedge Loudspeakers. A special floor monitor developed for the Dave Matthews Band that utilizes a tactile transducer (like the one found in drummers butt thumpers) to produce a tactile pounding on the musicians foot.
foreground music Officially music with (or without) lyrics and performed by the original artist. Used where it is believed people will pay attention to it. Contrast with background music.
formant Any of several frequency regions of relatively great intensity in a sound spectrum, which together determine the characteristic quality of a vowel sound. [AHD] Formants are what you emphasis in a sound system (or hearing aid) to improve intelligibility.
forward masking See temporal masking.
Four Elements Hip-Hop. The four elements of hip-hop culture were outlined by DJ Afrika Bambaataa in the late '70s as being DJing, MCing, breaking and graffiti writing.
Fourier analysis Mathematics. Most often the approximation of a function through the application of a Fourier series to periodic data, however it is not restricted to periodic data. [The Fourier series applies to periodic data only, but the Fourier integral transform converts an infinite continuous time function into an infinite continuous frequency function, with perfect reversibility in most cases. In this sense, it is not an approximation. The DFT and FFT are examples of the Fourier series, but are not approximations either unless the time data is an approximation itself, such as for sampled data systems, which introduces sampling errors.]
Fourier, Baron Jean Baptiste Joseph (1768-1830) French mathematician and physicist who formulated a method for analyzing periodic functions and studied the conduction of heat. [AHD]
Fourier transform A circuit analysis technique that decomposes or separates a waveform or function into sinusoids of different frequency which sum to the original waveform. It identifies or distinguishes the different frequency sinusoids and their respective amplitudes [Brigham, E. Oren, The Fast Fourier Transform and Its Applications, Englewood Cliffs, NJ: Prentice-Hall, Inc., 1988.]
fps (frames per second) See: frame.
FracRack (Fractional Rack) Nickname for 3U high 19" wide powered rack designed to accommodate modular synthesizer modules available from many manufacturers. First introduced by PAiA, called FracRak™. Similar to Eurorack with minor (but important) differences; also similar but very different from 500 Series card frames.
frammel Loudspeakers. In arrays it is sometimes necessary to separate and angle the cabinets a small amount to reduce phase interference. This is often done using a narrow wood strip called a frammel. [For reasons I cannot determine. If you know the origin of this word, write me.]
FRAP (flat response audio pick-up) Transducers. A type of piezoelectric pick-up developed by Arnie Lazarus in the late '60s. Made famous by attaching them to the Golden Gate Bridge and recording its sounds. [Really!]
Freed, Alan (1921-1965) Famous American radio disc jockey who jump-started the rock 'n' roll revolution that shook up the last half of the 20th century.
free field or free sound field A sound field without boundaries or where the boundaries are so distant as to cause negligible reflections over the frequency range of interest. Note that if the boundaries exist but completely absorb the sound then a virtual free field is created, thus anechoic chambers are used to measure loudspeakers.
free-field room (aka anechoic room) Acoustics. A room whose boundaries absorb effectively all the sound incident thereon, thereby providing essentially free-field conditions. [Harris]
frequency 1. The property or condition of occurring at frequent intervals. 2. Mathematics. Physics. The number of times a specified phenomenon occurs within a specified interval, as: a. The number of repetitions of a complete sequence of values of a periodic function per unit variation of an independent variable. b. The number of complete cycles of a periodic process occurring per unit time. c. The number of repetitions per unit time of a complete waveform, as of an electric current. [AHD]
frequency modulation See: FM.
frequency-modulation (friction) noise See: scrape flutter.
frequency response Audio electronics. It connotes amplitude-frequency response and quantifies a device's maximum and minimum frequency for full-output response. The electrical passband of an audio device. The measure of any audio device's ability to respond to a sine wave program, and therefore is a complex function measuring gain and phase shift (see phasor). It is used to express variation of gain, loss, amplification, or attenuation as a function of frequency, normally referred to a standard 1 kHz reference point.
frequency response of musical instruments See: musical instrument frequency ranges
fricative Phonology. A consonant, such as f or s in English, produced by the forcing of breath through a constricted passage. Also called spirant. [AHD]
friction noise See: scrape flutter
Frying Pan See: George Beauchamp.
FSK See: frequency shift keying.
FSM (Feedback Stability Margin ) Acoustics. The acoustic gain safety margin for a sound system to minimize acoustic feedback problems, usually set at 6 dB.
full duplex Redundant term. See duplex.
full-range Any audio device capable of capturing, reproducing or processing the full audio frequency spectrum of 20 Hz to 20 kHz.
full tilt boogie Slang phrase combining "full tilt" from the alternate word for jousting at top speed and "boogie" meaning to dance, so it means dancing at full speed.
Fuji Rock Festival Started in 1997 by Hidaka Masa, the festival aims at changing the way Japanese fans "listen to music," offering the possibility of hearing sounds for the very first time, in an atmosphere of "freedom" while camping surrounded by nature. ["Try Audio Provides Audio System for Fuji Rock Festival," FOH, November 2013]
fundamental Music. The first harmonic in a harmonic series; the lowest harmonic. Physics. The lowest frequency of a periodically varying quantity or of a vibrating system. [AHD]
fusion zone Acoustics & Hearing. All reflections arriving at the observer's ear within 20 -to-40 msec of the direct sound are integrated, or fused together, with a resulting apparent increase in level. [Everest & Pohlmann]
fuzz box also fuzzbox One of the earliest guitar effects units made popular in the '60s psychedelic and heavy metal sound. Early fuzz boxes were not much more than a heavy clipped signal, which tends to sound clarinet-like due to it squaring up the signal which adds lots of odd harmonics characteristic of the clarinet.
fuzzy clustering Mathematics. Analysis technique where complex problems are divided into groups or "clusters" for easier understanding. When the division between clusters is not sharp then you have "fuzzy" clusters that more accurately model real life situations. The importance to pro audio comes from it's use in modeling acoustic fields to predict SPL and other phenomena (for instance see Sunil Bharitkar and Chris Kyriakakis, "A Cluster Centroid Method for Room Response Equalization at Multiple Locations").
F-wrench Slang term for vernier calipers due to their resemblance to the letter "F."
FX unit Slang for "effects unit." See: effects boxes.