H The symbol for henry, a measure of inductance.
h Plank's constant, 6.626 × 10-34 joules-sec.
Haas Effect Also called the precedence effect, describes the human psychoacoustic phenomena of correctly identifying the direction of a sound source heard in both ears but arriving at different times. Due to the head's geometry (two ears spaced apart, separated by a barrier) the direct sound from any source first enters the ear closest to the source, then the ear farthest away. The Haas Effect tells us that humans localize a sound source based upon the first arriving sound, if the subsequent arrivals are within 25-35 milliseconds. If the later arrivals are longer than this, then two distinct sounds are heard. The Haas Effect is true even when the second arrival is louder than the first (even by as much as 10 dB.). In essence we do not "hear" the delayed sound. This is the hearing example of human sensory inhibition that applies to all our senses. Sensory inhibition describes the phenomena where the response to a first stimulus causes the response to a second stimulus to be inhibited, i.e., sound first entering one ear cause us to "not hear" the delayed sound entering into the other ear (within the 35 milliseconds time window). Sound arriving at both ears simultaneously is heard as coming from straight ahead, or behind, or within the head. The Haas Effect describes how full stereophonic reproduction from only two loudspeakers is possible. (After Helmut Haas's doctorate dissertation presented to the University of Gottingen, Gottingen, Germany as "Über den Einfluss eines Einfachechos auf die Hörsamkeit von Sprache;" translated into English by Dr. Ing. K.P.R. Ehrenberg, Building Research Station, Watford, Herts., England Library Communication no. 363, December, 1949; reproduced in the United States as "The Influence of a Single Echo on the Audibility of Speech," J. Audio Eng. Soc., Vol. 20 (Mar. 1972), pp. 145-159.)
Hafler, David (1919-2003) American engineer, inventor and member of the Audio Hall of Fame, considered one of the fathers of high fidelity. He founded Acrosound (1950), Dynaco (1954) and the David Hafler Company (1972).
half-duplex Pertaining to a transmission over a circuit capable of transmitting in either direction, but only one direction at a time. See also duplex.
half-normalled See: patchbay.
half-step or half-tone Music. 1. A marching step of 15 inches (38 centimeters) at quick time and 18 inches (46 centimeters) at double time. [AHD] 2. A pitch change equivalent to that produced by two adjacent piano keys. A semitone.
Hall effect or Hall voltage In a semiconductor, the Hall voltage is generated by the effect of an external magnetic field acting perpendicularly to the direction of the current.
Hall, Edwin Herbert (1855-1938) American physicist best known for his 1879 discovery of the Hall effect.
hamster switch DJ Mixers. A control found on professional DJ performance mixers that reverses fader action. For example, if a fader normally is off at the bottom of its travel and on at the top of its travel, then activating the hamster switch reverses this, so off is now at the top and on is at the bottom of travel, or alternatively, it swaps left for right in horizontally mounted faders. Used to create the most comfortable (and fastest) fader access when using either turntable, and to accommodate left-handed and right-handed performers. Credited to, and named by DJ Quest, one of the original scratch-style crews named The Bullet Proof Scratch Hamsters.
handshaking The initial exchange between two communications systems prior to and during transmission to ensure proper data transfer.
Hangout Music Festival A 3-day music festival located on an Alabama beach.
happiness "An agreeable sensation arising from contemplating the misery of another." — Ambrose Bierce.
haptic Of or relating to the sense of touch; tactile. [AHD]
Hardanger fiddle Musical Instrument. An 8 (or 9) string violin, indigenous to Norway, that is narrower and shorter-necked than a normal violin.
hardart Musical Instruments. A type of keyboard invented by the composer Philip Glass, which is used to play other instruments. Click the link for the whole story.
hard bop A simpler and more rhythmic variation of bebop; referring mostly to East Coast jazz performed mainly by black musicians.
hard clipping See clipping.
hard disk A sealed mass storage unit used for storing large amounts of digital data.
hard-drawn copper wire See Thomas Doolittle.
Hard Summer Music Festival Very eclectic music and performance festival held in various cities across North America.
hardware The physical (mechanical, and electrical) devices that form a system.
hardware key See: dongle.
hardwired 1. To connect (electronic components, for example) by electrical wires or cables. 2. To implement (a capability) through logic circuitry that is permanently connected within a computer and therefore not subject to change by programming. 3.a. To determine or put into effect by genetic inheritance: "It may be that certain orders of anxiety are hardwired in us" (Armand Schwerner). b. To provide with a response or capability by genetic inheritance: Humans are hardwired for speech. [AHD]
Hardy Martin See: Martin, Hardy.
Harley-Davidson It is a common misconception that the sound of a Harley is trademarked. It is not; although they did try. An application was filed on February 1, 1994, describing it as "The mark consists of the exhaust sound of applicant's motorcycles, produced by V-Twin, common crankpin motorcycle engines when the goods are in use." The application was never granted and was abandoned on September 22, 2000. For interesting reading see Michael Sapherstein, "The Trademark Registrability of the Harley-Davidson Roar: A Multimedia Analysis."
harmonic 1. Any of a series of musical tones whose frequencies are integral multiples of the frequency of a fundamental tone. 2. A tone produced on a stringed instrument by lightly touching an open or stopped vibrating string at a given fraction of its length so that both segments vibrate. Also called overtone, partial, partial tone. A marching step of 15 inches (38 centimeters) at quick time and 18 inches (46 centimeters) at double time. Contrast with ultraharmonic.
harmonica A small rectangular wind instrument with free reeds recessed in air slots from which tones are sounded by exhaling and inhaling. [MWD]
harmonic distortion See THD.
harmonicity The degree to which a sound's timbre conforms to a harmonic series (Thanks to Scott Wilkinson for this succinct definition).
harmonic series 1. Mathematics. A series whose terms are in harmonic progression, such as 1 + 1/2 + 1/3 + 1/4 + 1/5 + ...
2. Music. A series of tones consisting of a fundamental tone and the overtones produced by it, and whose frequencies are consecutive integral multiples of the frequency of the fundamental. [AHD]
Harrison, David (1942-1995) American musician and engineer who founded Harrison Consoles. He pioneered the modern "in-line" audio console in 1970, licensing his first design to MCI who sold it as the MCI 400.
Harrison, Ercel B. American engineer who was the chief designer at Peerless Transformers, where he designed the first full frequency transformers for the motion picture industry. He is regarded as a legend of transformer design and innovation.
harrumph To make a show of clearing one's throat. [AHD]
HATS (head and torso simulator) Acoustics. A dummy head, with artificial ears and ear canals fitted with microphones, and a torso, used to measure acoustic parameters.
HAVi (Home Audio/Video interoperability) An industry standard for home networks designed to link consumer electronics products. Developed by eight consumer giants — Grundig, Hitachi, Panasonic, Philips, Sharp, Sony, Thomson Multimedia and Toshiba -- the main aim of this protocol is to ride on IEEE 1394 interface, connecting digital TVs, set-top boxes, DVD players and other digital consumer products.
HDBaseT Abbr. HDBT Networking. A multimedia connectivity standard optimized for full uncompressed HD video, audio, 100Base-T Ethernet, power over cable and various control signals through a single Cat 5e cable.
hdCD (high density compact disc) See DVD.
HDCD (high definition compatible digital) Pacific Microsonics' (now owned by Microsoft) trademark for their encode/decode scheme that allows up to 24 bit, 176.4 kHz digital audio mastering process, yet is compatible with normal 16 bit, 44.1 kHz CD and DAT formats. Claimed to sound superior even when not decoded, and to be indistinguishable from the original if decoded.
HDD (high-capacity hard disk drive) See: HDR below.
HDR (hard-disk recorder) An audio recording device based on computer hard disk memory technology. Typically, these machines are configured like analog tape recorders offering 24-48 tracks, utilizing 24-bit / 48-96 kHz data converters with optional I/O to interface with ADAT, TDIF, or AES3, and file format interchangeability with DAWs.
HDTV (high definition television) The standard for digital television in North America, still being revised. When finished will include a definition for picture quality at least that of a movie theater, or 35 mm slide, i.e., at least two million pixels (compared to 336,000 pixels for NTSC).
head amp Electronics. 1. A pre-preamplifier or simply a preamplifier. A very low noise, high gain audio preamp used to boost signal levels from very low sources such as moving coil phono cartridges, some acoustic pick-ups, etc. 2. Slang for headphone amplifier. 3. A guitar amplifier without speakers that usually sits on top of and forms the "head" of a loudspeaker stack, classically comprised of two cabinets consisting of four 10" or 12" drivers each. Also called amp head.
headphones An electromagnetic transducer usually based on the principle of electromagnetic induction used to convert the electrical energy output of a headphone amplifier into acoustic energy. Popular nickname:"cans."
headphone sensitivity See sensitivity.
headroom A term related to dynamic range, used to express in dB, the level between the typical operating level and the maximum operating level (onset of clipping). For example, a nominal +4 dBu system that clips at +20 dBu has 16 dB of headroom. Because it is a pure ratio, there are no units or reference-level associated with headroom — just "dB." Therefore (and a point of confusion for many) headroom expressed in dB accurately refers to both voltage and power. Which means our example has 16 dB of voltage headroom, as well as 16 dB of power headroom. It's not obvious, but it's true. (The math is left to the reader.)
headshell Turntables. The removable part of the cartridge mounting assembly attached to the end of the turntable arm.
HeadWize A now defunct non-profit (i.e., no ads) site specializing in headphones and headphone listening, featuring articles, essays, projects and technical papers on all things headphone — very informative.
H.E.A.R. (Hearing Education and Awareness for Rockers) A non-profit volunteer organization dedicated to raising awareness of the real dangers of repeated exposure to excessive noise levels from music which can lead to permanent, and sometimes debilitating, hearing loss and tinnitus.
hearing Perceiving sound by the ear. [AHD] See "What Is Up With Noises?" by Vi Hart [Absolutely brilliant contribution by a true genius. Hit the link on her name and check out her home page; you won't be disappointed.] Also for the best presentation of the medical details of hearing see "Auditory Transduction" by Brandon Pletsch. He marries symphony with digital graphics guaranteed to stimulate and educate.
hearing, extreme The record for the most extreme hearing range goes to the moth, who detects frequencies up to 300 kHz, followed by dolphins, who can hear up to 160 kHz.
heat sink Electronics. A protective device that absorbs and dissipates the excess heat generated by a system. [AHD] Generally a mass of metal (usually aluminum) having much greater thermal capacity than the attached heat source. Also see: Kordyban.
Heaviside, Oliver (1850-1925) British self-taught engineer, mathematician and physicist, a giant among giants who independently discovered Laplace-like operatives used to simplify differential equations and covenanted vector analysis which he used to reformulate Maxwell's equations (from twenty equations to the famous four of today). [All this before breakfast.]
heavy-metal Music. A form of rock music characterized by extreme volume, high-intensity electric guitar, flashy costumes and dramatic stage performances. Originally coined by William Burroughs in his book, Naked Lunch, it was first voiced in music, "heavy-metal thunder," in Steppenwolf's "Born to be Wild." The song believed to be the first heavy-metal piece was a remake of Eddie Cochran's "Summertime Blues" recorded by Blue Cheer in 1968. [McCleary]
hecto- or hect- Mathematics. Prefix meaning one hundred (10²
hectometer Abbr. hm A metric unit of length equal to 100 meters. [AHD]
HEI (House Ear Institute) Established in 1946, a private nonprofit organization, with an international reputation as a leader in its field through its applied otologic research and education programs.
Heinrich See: discotheque
Heisenberg uncertainty principle "The more precisely the position is determined, the less precisely the momentum is known in this instant, and vice versa." — Heisenberg, uncertainty paper, 1927.
Helmholtz Equation Used in acoustics and electromagnetic studies. It arises, for example, in the analysis of vibrating membranes, such as the head of a drum, or in solving for room modes. (After Hermann Ludwig Ferdinand von Helmholtz below.)
Helmholtz, Hermann Ludwig Ferdinand von (1821-1894) German physicist and physiologist who formulated the mathematical law of the conservation of energy (1847) and invented an ophthalmoscope (1851) [AHD] (An instrument for examining the interior structures of the eye, especially the retina, consisting essentially of a mirror that reflects light into the eye and a central hole through which the eye is examined. You aren't a real doctor without one.) Famous for his book, On the Sensations of Tone first published in 1862.
Helmholtz resonator When you blow air across the top of an empty bottle to make a sound, you are demonstrating the principal of a Helmholtz resonator. Click the link to read the details and do the math.
hemi-anechoic room Acoustics. A test room with a hard reflective floor but whose other surfaces absorb essentially all the incident sound, thereby providing free-field conditions above the reflective plane. [Harris]
Hertz, Heinrich Rudolf (1857-1894) German physicist who was the first to produce radio waves artificially. [AHD]
heterodyne Radio & Television. Having alternating currents of two different frequencies that are combined to produce two new frequencies, the sum and difference of the original frequencies, either of which may be used in radio or television receivers by proper tuning or filtering. [AHD]
heterophony Music. The simultaneous playing or singing of two or more versions of a melody. [AHD]
heuristic Computer Science. Relating to or using a problem-solving technique in which the most appropriate solution of several found by alternative methods is selected at successive stages of a program for use in the next step of the program. [AHD]
hexadecimal A number system using the base-16, i.e., each number can be any of 16 values. Normally represented by the digits 0-9, plus the alpha characters A-F. A four-bit binary number can represent each hexadecimal digit.
Heyerdahl, Thor (1914-2002) Norwegian anthropologist and explorer made famous by his book Kon-Tiki about his epic 1947 expedition voyage to Polynesia.
On a visit to London, Heyerdahl had a busy schedule of appointments. Shortly after recording a program for the Independent Television Network, he was due at the BBC studios for an interview. Having been assured by the BBC that a taxi would be sent to pick him up from the ITN studios, Heyerdahl waited expectantly in the lobby. As the minutes ticked by, however, he began to grow anxious. He approached a little man in a flat cap, who looked as if he might be a taxi driver and was obviously searching for someone. "I'm Thor Heyerdahl," said the anthropologist, "Are you looking for me?" "No, mate," replied the driver. "I've been sent to pick up four Airedales for the BBC." [Bartlett's Book of Anecdotes]
HF See: frequency bands.
H(ermon) H(osmer) Scott (1909-1979) American engineer most famous for his very successful and important contributions to consumer hi-fi systems.
Hi8 See DA-88.
hichiriki Musical Instrument. A type of Japanese flute.
HID (Human Interface Device) Click the link for details.
hide A set of drums. [Decharne]
high-cut filter also hi-cut filter See low-pass filter [In audio electronics, we define things like this just to make sure you're paying attention.] Contrast with high-pass filter below.
higher order ambisonics See: HOA
high impedance Abbr. Hi-Z Electronics. A device having an electrical impedance of at least 2,000 ohms. [Note: This value is arbitrary as there is no standard defining exactly what constitutes a 'high impedance.'] Examples include headphones rated 600 ohms and up (headphone division between hi-Z and lo-Z is lower than other devices); microphones rated 10k - 100k ohms; and most circuit inputs are high-impedance, rated at 2k-100k ohms. Contrast with low impedance.
highlife Music. Popular West African dance music that combines African rhythms and Western-style pop melodies.
high-pass filter also hi-pass filter A filter having a passband extending from some finite cutoff frequency (not zero) up to infinite frequency. An infrasonic filter is a high-pass filter. Also known as a low-cut filter.
Hilliard, John Kenneth (1901-1989) American physicist and distinguished acoustical engineer who began his career pioneering audio soundtracks for movies.
Hi-NRG (High Energy) From the Evelyn Thomas disco hit, "High Energy." A form of electronic dance music popular in the '80s.
hip-hop Music. A musical genre term whose origin is still debated, but most credit Afrika Bambaataa and the Zulu Nation who used the term in the late '70s to describe their South Bronx block parties. Afrika Bambaataa credits Lovebug Starski as the first to use the term to relate to the hip-hop culture.
hiss Random high frequency noise with a sibilant quality, most often associated with tape recordings. Acoustics. Term for noise in the 2 kHz to 8 kHz range.
histogram A bar graph of a frequency distribution in which the horizontal axis lists each unique value (or range of values) in a set of data, and the height of each bar represents the frequency (or relative frequency) of that value (or range of values). [AHD]
History of Concert Sound Great repository of concert sound history created by Doug Fowler.
Hi-Z See high impedance.
hoaxes, audio See Bob Pease's wonderful "What's All This Hoax Stuff, Anyhow?"
hokey 1. Mawkishly sentimental; corny. 2. Noticeably contrived; artificial. [AHD]
hokey-pokey (also UK: hokey-cokey) A popular song and line dance whose origins is a bit cloudy. Hit the link for history.
holodigital square Mathematics. Square number containing each decimal digit exactly once, e.g., 9,814,072,356 is the largest example (i.e., 99,0662).
Holophonics An acoustical recording and broadcast technology claimed to be the aural equivalent to holography, hence the name. Holophonics is an encode process that occurs during the recording session using a special listening device named "Ringo." It is claimed that "playback or broadcast is possible over headphones or any existing mono or stereo speaker system, with various levels of spatial effect. Optimal effects occurs when two tracks (stereo) are played utilizing digital technology over headphones and minimal effect when played over a single mono speaker (two tracks merged into one and played over a single speaker)."
HomeRF Lite See ZigBee.
homicide "The slaying of one human being by another. There are four kinds of homicide: felonious, excusable, justifiable and praiseworthy, but it makes no great difference to the person slain whether he fell by one kind or another — the classification is for advantage of the lawyers." -- Ambrose Bierce.
hope "Desire and expectation rolled into one." — Ambrose Bierce.
horn Loudspeakers. A sound radiator cone mounted onto a loudspeaker diaphragm to amplify its output based on the same principal found in musical instrument horns.
Horner, William George (1786-1837) English mathematician and inventor of the Zoetrope.
horse-head fiddle See: morin khuur.
hot swap A disconnection of a subcomponent and a reconnection of the same or a replacement component without first turning off the power at the connection interface. [IEEE]
hot water Running hot water has a lower pitch than running cold water.
hourglass drum See: talking drum.
house curve Sound Reinforcement. The name given to the weighting, or alteration, of the sound equalization for a room. It is a rule-of-thumb for what to do after achieving the flattest possible response. Different venues require different house curves with wide variation between many favorites. The most common one is for speech reinforcement in large auditoriums (only) and measures 10 dB down at 10 kHz with respect to 1 kHz (this is a 3 dB/octave slope). This contrasts to the 2 -3 dB used in many small control rooms. The proper choice is heavily dependent on the source material (speech vs. music) and the venue (large vs small; reverberant or dry); there is no one standard.
House Ear Institute See HEI.
house mixer See FOH.
house sync A distributed master signal used to guarantee all digital devices run at the same speed. Hit the link for details.
HOW (house of worship) Generic term for any structure used for religious gathering, includes churches, synagogues, temples and mosques; a sacred space.
howlround What the British call acoustic feedback.
H-PAS (Hybrid Pressure Acceleration System) Loudspeakers. A proprietary loudspeaker technology licensed Atlantic Technology, in collaboration with Solus/Clements Loudspeakers, based on a concept developed by Philip R. Clements circa 1979 (U.S. patent 4,373,606, Loudspeaker enclosure and process for generating sound radiation, granted on February 15, 1983). Not relying on electronics, this bass extending idea uses a specially designed chamber to acoustically amplify low frequencies, e.g., a -3dB point of 28 Hz for a single 5 1/4" driver is achievable.
HpTF (headphone transfer function) The complete transfer function from source to the ear-canal, taking into effect the influence of headphone coupling and position on the ear. Hit the link for one scholarly experiment, results and discussion.
HRA (High-Resolution Audio) An initiative by the Digital Entertainment Group (joined by CEA, AES, et al.) to define and mark file- or physical-media based sources of digital audio that qualify as true high-fidelity products. The official definition is “lossless audio that is capable of reproducing the full range of sound from recordings that have been mastered from better than CD quality music sources.”
HRIR (head-related impulse response) See: HRTF.
HRMAI (high-resolution multichannel audio interconnection) From AES standard AES50: AES Standard for digital audio engineering — High-resolution multichannel audio interconnection (HRMAI). "A high- performance point-to-point audio interconnection rather than a network, although the auxiliary data may operate as a true network, independently of the audio." Also see the companion application document AES-R6: AES project report — Guidelines for AES standard for digital audio engineering -- High Resolution multichannel audio interconnection (HRMAI). Download both here.
HRRC (Home Recording Rights Coalition) An advocacy group that includes consumers, retailers, manufacturers and professional servicers of consumer electronics recording products.
HRTF (head-related transfer function) The impulse response from a sound source to the eardrum is called the head-related impulse response (HRIR), and its Fourier transform is called the head-related transfer function (HRTF). The HRTF captures all of the physical cues to source localization, and is a surprisingly complicated function of four variables: three space coordinates (azimuth, elevation & range) and frequency, and to make matters worst, they change from person to person. Interaural (i.e., between the ears) time differences, interaural time delays and the physical effects of diffraction of sound waves by the torso, shoulders, head and pinnae modify the spectrum of the sound that reaches the eardrums. These changes allow us to localize sound images in 3D space and are captured by the HRTFs. HRTFs have been named and studied since at least the early '70s [Blauert]
HTML (hypertext markup language) The software language used on the Internet's World Wide Web (WWW). Used primarily to create home pages containing hypertext.
HTTP (hypertext transfer protocol) The name for the protocol that moves documents around the Internet/Web. Used by the various servers and browsers to communicate over the net.
hub 1. In broadband LAN use, a central location of a network that connects network nodes through spokes, usually in a star architecture. Think of it as a digital splitter, or distribution amplifier. 2. In complex systems, hubs perform the basic functions of restoring signal amplitude and timing, collision detection and notification, and signal broadcast to lower-level hubs.
Huffman coding or Huffman algorithm One of the MP3 and AAC techniques used in digital audio data compression. While not a compression technique in itself, it is used in the final steps to code the process, and is an ideal complement of the perceptual coding. Huffman codes are used in nearly every application that involves the compression and transmission of digital data, such as fax machines, modems, computer networks, and high-definition television. For more details, see: Huffman Coding [After David Huffman (1925-1999).]
Hughes, David Edward (1831-1900) Welsh-American musician and scientist recognized as the coinventor of the microphone and teleprinter, and inventor of the crystal radio.
huh See: www.huhcorp.com. [Some things are too clever, creative and funny to explain; they are better left experienced. Enjoy.]
hullabaloo Great noise or excitement; uproar; disorderly tumult together with loud, bewildering sound. The lagging of an effect behind its cause, as when the change in magnetism of a body lags behind changes in the magnetic field.
Humanthesizer Hit the link to read & see performance artist Calvin Harris take MIDI to a new extreme as created by Phil Clandillon and Steve Milbourne of Sony/BMG.
humbucking pickup Musical Instruments. A pickup arrangement usually found on electric guitars designed to reduce the effects of 50 Hz or 60 Hz hum products. Typically this is done using two pickups wired electrically and magnetically opposite so as to cancel (buck) induced hum and other noise interference. Invented by engineer Seth Lover at Gibson and patented as US 2,896,491 granted in 1959 but filed in 1955, and first appeared on Gibson steel guitars in 1956 and then on the legendary Les Paul models beginning in 1957. Leo Fender received his humbucking pickup patent, US 2,817,261 in 1957 after filing in 1956.
hum components The harmonics of the AC mains supply. The Americas (except the southern half of South America), Japan, Taiwan, Korea and the Philippines use a 60-Hz system, placing the most annoying 2nd and 3rd harmonics at 120 Hz and 180 Hz. For Europe, and the rest of the world using 50-Hz mains, these components fall at 100 Hz and 150 Hz.
huqin Musical Instrument. Chinese bowed string instruments.
hurdy-gurdy Musical Instrument. 1. A medieval stringed instrument played by turning a rosined wheel with a crank and depressing keys connected to tangents on the strings. 2. Any instrument, such as a barrel organ, played by turning a crank. [AHD] (Hit the link for photos of this strange and wonderful instrument.)
hybrid Telecommunications. A term used to describe an interface box that converts a conversation (or data signal) coming in on two pairs (one pair for each direction of the conversation or signal) onto one pair and vice versa (i.e., a 2-wire to 4-wire converter). This is necessary because all long distance circuits are two pairs, while most local circuits are one pair. The name comes from the original use of a "hybrid coil" in the telephone whose function was to keep the send and receive signals separated. Both analog and digital hybrid designs are found. A fundamental (and unavoidable) problem in any 2-wire to 4-wire design is leakage (crosstalk) between the transmit and receive signals. In analog designs leakage is reduced by modeling the impedance seen by the transmit amplifier as it drives the hybrid coil. Because telephone-line impedance is complex and not well modeled by a simple passive RLC circuit, only 10 dB to 15 dB of leakage reduction is usually possible. Digital hybrids use DSP technology to model and dynamically adapt to provide much greater reduction than analog designs, typically resulting in reductions of 30 dB to 40 dB. However, the best digital hybrids incorporate acoustic echo cancelling (AEC) circuitry to gain even greater improvements. The AEC works to cancel out any remaining signal coming from the loudspeaker (far-end received signal) from the microphone signal before they can be retransmitted to the far end as acoustic echo. Digital hybrids with AEC achieve total leakage reduction of 50 dB to 65 dB.
hybrid shield termination Audio wiring. The name for the termination technique where the shield is bonded to the sending end's metal chassis and is capacitively-coupled to the receiving end's metal chassis. For an example of a connector designed for this see Neutrik's EMC-XLR.
hydrophilic Having an affinity for water; readily absorbing or dissolving in water. [AHD]
hypercardioid microphone See cardioid microphone.
HyperPhysics A website concept created by Carl R. (Rod) Nave, Department of Physics and Astronomy, Georgia State University. "An exploration environment for concepts in physics which employs concept maps and other linking strategies to facilitate smooth navigation." [An incredible site. You can get lost here for hours. I can't recommend it enough.]
hypersonic sound Term that describes the emerging audio technology of using wireless ultrasonic signals and nonlinear signal mixing techniques to produce sound located only in very specific areas. First discovered and described by Helmholtz in the late 1800s, it is now finding use in ATMs, dynamic signage and museum exhibits. For examples see: American Technology Corporation's HSS® HyperSonic Sound products and Sennheiser's Audiobeam.
hypertext Within WWW documents, the linking of words to other sections of text, pictures or sound is called hypertext. Hypertext is created using the HTML software language. Also used frequently in Help files.
hysteresis Magnetism& Electronics. The lagging of an effect behind its cause, as when the change in magnetism of a body lags behind changes in the magnetic field. [AHD] The maximum difference in value for a digitizer code transition level when the transition level is approached from either side of the transition. [IEEE] In simple terms a circuit that has a different threshold point going high than it does going low. The phenomenon was identified, and the term coined, by Sir James Alfred Ewing in 1890. [From Wikipedia: hysteresis]
Hz See: hertz.