Digital music, indeed most computer stuff these days, attracts it's share of abbreviations and acronyms... so many in fact that, as much as I've tried to make this site accessible to all users - including speech-enabled browsers, this area is the most time-consuming to code.

Therefore, these glossary pages are the best place for "decrypting" those acronyms.

Music glossary pages:

Alphabetical Digital Audio Glossary: Letters H-M

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Haas effect

The discovery of this effect is attributed to Halmut Haas in 1949.

If sounds arrive from several sources, the ears and brain will identify only the nearest. In other words, if our ears receive similar sounds coming from various sources, the brain will latch onto the sound that arrives first. If the time difference is up to 50 milliseconds, the early arrival sound can dominate the later arrival sound, even if the later arrival is as much as 10 dB louder.

Hard disk recording

Process by which audio data is loaded to hard disk.


Also called overtones, these are vibrations at frequencies that are multiples of the fundamental.

Harmonics extend without limit beyond the audible range. They are characterized as even-order and odd-order harmonics. A second-order harmonic is two times the frequency of the fundamental; a third order is three times the fundamental; a fourth order is four times the fundamental; and so forth.

Each even-order harmonic: second, fourth, sixth, etc... is one octave, or multiples of one octave, higher than the fundamental; these even-order overtones are therefore musically related to the fundamental.

Odd-order harmonics, on the other hand: third, fifth, seventh, and up-create a series of notes that are not related to any octave overtones and therefore may have an unpleasant sound. Audio systems that emphasize odd-order harmonics tend to have a harsh, hard quality.


High-Definition Compact Disc.

A proprietary system by Pacific Microsonics that requires special encoding during the recording process. Some observers report HDCD discs as having better sound. To gain the benefits requires having special HDCD in your CD player.


The ability of an amp to go beyond its rated power for short durations in order to reproduce musical peaks without distortion. This capability is often dependent on the power supply used in the design.

Head Unit

The in dash control center of a car audio system, usually consisting of an internal low powered amp, AM/FM receiver, and either a tape or CD player (or both).

Hearing Sensitivity

The human ear is less sensitive at low frequencies than in the midrange. Turn your volume knob down and notice how the bass seems to"disappear". To hear low bass requires an adequate SPL level. To hear 25Hz requires a much higher SPL level than to hear 250Hz. In the REAL world, low frequency sounds are reproduced by large objects; bass drums, string bass, concert grand pianos, etc. Listen to the exhaust rumble of a 454 cubic inch V8 engine vs. the whine of the little four banger. The growl of a lion vs. the meow of your favorite kitty. As frequency decreases we perceive more by feel than actual hearing and we lose our ability to hear exact pitch.

Hertz (Hz)

A unit of measurement denoting frequency, originally measured as:
Cycles Per Second (CPS): 20 Hz = 20 CPS. Kilohertz (kHz) are hertz measured in multiples of 1,000.

High-end music studio

Studio environment that is equipped with exceptionally high-quality, exorbitantly expensive devices.

High-Pass Filter

A circuit that allows high frequencies to pass but rolls off the low frequencies. When adding a subwoofer it is often desirable to roll-off the low frequencies to the main amplifiers and speakers. This will allow the main speakers to play louder with less distortion. High-pass filters used at speaker level are usually not very effective unless properly designed for a specific main speaker (see impedance below).

Home Theater

An audio system designed to reproduce the theater sound experience while viewing film at home. Minimally consisting of a Dolby Pro Logic® surround sound receiver, left and right front speakers, a center channel speaker, and two surround speakers. These plus optional subwoofer(s), surround speaker(s), and digital formats such as Dolby Digital® can enhance the viewing experience by drastically improving the sound quality of movie soundtracks.



Listening term. A good stereo system can provide a stereo image that has width, depth and height. The best imaging systems will define a nearly holographic re-creation of the original sound


Impedance is a measure of electrical resistance specified in ohms. Speakers are commonly listed as 4 or 8 ohms but speakers are reactive devices and a nominal 8 ohm speaker might measure from below 4 ohms to 60 or more ohms over its frequency range. This varying impedance curve is different for each speaker model and makes it impossible to design a really effective "generic" speaker level high-pass filter. Active devices like amplifiers typically have an input impedance between about 10,000-100,000 ohms and the impedance is the same regardless of frequency.

Inductance (L)

The capability of a coil to store energy in a magnetic field surrounding it. It produces an impedance to an ac current. Inductors are commonly used in audio as low pass crossovers. 

Infinite Baffle

A baffle that completely isolates the back wave of a driver from the front without a standard enclosure. 

Infrasonic (Subsonic) Filter

A filter designed to remove extremely low frequency (25Hz or lower) noise from the audio signal. Useful for Ported box designs.


Cables that are used to connect components at a low signal level. Examples include CD player to receiver, pre-amplifier to amplifier, etc. Most interconnects use a shielded construction to prevent interference. Most audio interconnects use RCA connections although balanced interconnects use XLR connections.

Isobarik Enclosure

A trade name for a compound enclosure. 

Insert effect

An effect that is inserted between an audio track and the mixer.


The beginning of an arrangement. It gradually introduces the song and slowly builds up musical tension.



A tendency towards lack of synchronization caused by electrical changes. Technically the unexpected (and unwanted) phase shift of digital pulses over a transmission medium. A discrepancy between when a digital edge transition is supposed to occur and when it actually does occur - think of it as nervous digital, or maybe a digital analogy to wow and flutter.



Material developed by Dupont that is has an exceptional strength to weight ratio. Used extensively in bullet-proof vests, skis, sailboat hulls, etc. In audio, used in many variations for speaker cones.

Kilohertz (kHz)

One thousand hertz.



This term describes the amount of time computers and audio hardware take to generate or process audio signals. It is the delay between the actual start of an event and the moment in which it becomes audible.

Linear frequency response

This means that the frequencies that make up an audio signal are rendered by audio hardware at levels that are directly proportionate to the input volume.

Line Level

CD players, VCRs, Laserdisc Players etc... are connected in a system at line level, usually with shielded RCA type interconnects. Line level is before power amplification. In a system with separate pre-amp and power-amp the pre-amp output is line level. Many surround sound decoders and receivers have line level outputs as well.


A speaker device that is long and tall. Imagine a narrow dowel dropped flat onto the water's surface. The line-source has very limited vertical dispersion, but excellent horizontal dispersion.


Any time more than one speaker device covers the same part of the frequency range there will be some unevenness in the output. (Picture the waves from one pebble dropped into a calm pool vs. two pebbles dropped several inches apart.) Lobing means that the primary radiation pattern(s) is at some angle above or below the centerline between the two drivers. Good crossover design takes this into account.


Another term for volume.

Low Frequency Extension

Manufacturers, writers and salespeople toss around all kinds of numbers and terminology that can be very confusing and misleading. "This $300 shoebox sized sub is flat to 20Hz". Right, in your dreams . . . How is that cheap, tiny box and driver going to reproduce a 56 foot wavelength with enough power to be heard?

It will not. Good bass reproduction requires moving a lot of air and playback at realistic volumes. Remember the rule of needing to move four times the air to go down one octave. Example: You have a pair of good quality tower speakers with 10" woofers that produce good bass down to around 40Hz. The salesman is telling you that his little subwoofer with a single 10" woofer will extend your system down to 20Hz.

If you've been paying attention, you know that his woofer will have to move eight times as much air as each of your 10" woofers, not likely. Adding that subwoofer to your system might give you more apparent bass energy, and in fact may help a little with movie special effects, but it is unlikely to extend bass response significantly.

Low-Pass Filter

A circuit that allows low frequencies to pass but rolls off the high frequencies. Most subwoofers have low-pass filters built in and many surround sound decoders have subwoofer outputs that have been low-pass filtered.


Magnetic-Planar Speakers

A type of speaker that uses a flat diaphragm with a voice coil etched or bonded to it to radiate sound. If the magnets are both in front of and behind the diaphragm, it becomes a push-pull magnetic-planar.


A process by which a mixed-down piece of music is given a final sonic and electronic buff; the final step before the track is burned onto CD.

(Mastering tutorial)

Maximum power rating

A meaningless specification. 


A unit of measure for processor clock frequency. This is a benchmark specification that provides some insight into the computing speed and performance capability of a computer.

Melody line

Single-note, instantly recognizable motif that conjures up a specific musical atmosphere.

MIDI (Musical Instrument Digital Interface)

Created in 1982, this is the industry standard governing the transmission of control commands for electronic music instruments and studio devices.

(MIDI tutorials)

MIDI adapter

A cable connector that turns the game-port of an audio card into a MIDI port.

MIDI event

A term used to describe an individual command or message sent via MIDI.

MIDI hardware

Any MIDI-compatible device.

MIDI instruments

Sound generators that can be played via MIDI.

MIDI interface

Accessory that connects MIDI devices to the computer.

MIDI keyboard

A keyboard used to play MIDI sound generators. It may or may not be equipped with an audio generator.


A speaker, (driver),  used to reproduce the middle range of frequencies.  A midrange is combined with a woofer for low frequencies and a tweeter for high frequencies to form a complete, full-range system.


A device that lets you voice or shape the signals of several audio sources and converge them into a single master audio signal.

(Mixing audio tutorial)


Software for the arrangement of music tracks on the basis of drum loops and other sampled phrases, distributed by Steinberg.

Monitoring environment

Combination of loudspeakers and amp by which audio signals are made audible.


Any speaker that encloses the backwave of the speaker device even though part of this backwave may be released via a port or duct. The primary radiation at most frequencies will be from the driver front. If the driver is not enclosed it becomes a dipole.


Metal Oxide Semiconductor Field Effect Transistors. Used in most modern, quality car audio amplifiers in the power supply (and sometimes in the output stage). MOSFET's run cooler than normal bipolar transistors, and have a faster switching speed.

MP3 (MPEG 1 Layer 3)

A data reduction process for audio files developed by Fraunhofer Institute; it has become the established format for distributing music over the Internet.


Listening term. A sound that is poorly defined, sloppy or vague. For example, a "muddy" bass is often boomy with all the notes tending to run together.


To greatly decrease the volume level. Many receivers and pre-amplifiers have a muting control which allows the volume level to be cut way down without changing the master volume control. Great for when the phone rings.

Multimedia software

Programs for playing back or processing static images, audio and video.


This describes a process in which several tracks are played back simultaneously, which allows a song to be recorded step by step rather than all at once.

Musician's portal

Website on which musicians can publish music and swap stories with other musicians.

Music production

The full sweep of musical activity involved in going from an idea to a finished song.