Welcome to Part One of our glossary of terms, a comprehensive guide designed to help you navigate the often complex world of high-end audio. As you delve deeper into the realm of audiophilia, you’ll encounter a rich and varied vocabulary that can sometimes seem like a language all its own.

This glossary aims to demystify that language, providing clear and concise explanations for a wide range of audio- related terms. From technical specifications to subjective descriptions of sound qualities, we’ve endeavored to cover the breadth of terminology you’re likely to encounter in your audiophile journey.

It’s important to note that while extensive, this glossary is not exhaustive. The world of high-end audio is vast, spanning numerous cultures and languages across the globe. Each region and community often contributes its own unique terms and expressions to the audiophile lexicon, making a truly complete compilation a near-impossible task.

Nevertheless, what I present here is a reasonably comprehensive list that should serve as a valuable resource for both newcomers and seasoned enthusiasts alike. Whether you’re trying to understand a review in an audio magazine, deciphering the specifications of a new piece of equipment, or simply aiming to communicate more effectively with fellow audiophiles, this glossary will be your guide.

As you explore these terms, remember that the language of audio is ever-evolving, much like the technology it describes. New terms emerge, old ones take on new meanings, and regional variations continue to enrich our shared vocabulary. This glossary, therefore, is not just a reference but an invitation to engage more deeply with the vibrant, global community of high-end audio enthusiasts.

So, whether you’re puzzling over impedance or trying to grasp the nuances of soundstage, you’ll find the answers here. Let this glossary be your companion as you continue your quest for audio perfection, helping you to understand and articulate the subtle qualities that make high-end audio such a rewarding pursuit.

Part Two of this glossary (N – Z) will appear in the next issue.

A-weighting — A form of electrical filter which is designed to mirror the sensitivity of the human ear to different frequencies at low sound pressure levels. The filter rolls-off the low frequencies below about 700Hz and the highs above about 10kHz. This filter is often used when measuring low- level sounds, like the noise floor of a device.

Absolute phase, absolute polarity — The preservation of the initial acoustic waveform all the way through the recording and reproducing system, so that a compression that reaches the original microphone will be reproduced in the listener’s system as a compression reaching his or her ears. A positive pressure on the microphone is reproduced as a positive pressure by the loudspeaker. For instance, the plosive “p” sound from a vocalist sends an initial positive air pressure wave toward the microphone, which responds with an initial inward movement of the microphone diaphragm, away from the vocalist, along with an identical positive air pressure wave at the loudspeaker.

AC — Alternating current. In audio, signals are represented in the electrical domain as currents flowing alternately forward and back (+/-) in the circuits, an analog of the compression and rarefaction of acoustic air pressure. In electrical power, AC is an electric current which reverses direction 50 or 60 times per second depending on the region, in contrast to direct current (DC) which flows only in one direction, as in a battery.

Acoustic foam — A specific type of open-cell, expanded polyurethane that allows sound waves to enter and flow through the foam, absorbing their energy by means of conversion to heat through friction, and preventing them being reflected. The density and depth of the foam affects the frequency range over which it is effective as an absorber.

Acoustic treatment — A generic term embracing a range of products or constructions intended to absorb, diffuse, or reflect sound waves in a controlled manner, designed to improve the overall sound character of the room by reducing reflections through absorption and scattering acoustic energy through diffusion.

Acuity — The sensitivity of ears to very soft sounds through circumstance or training, used to hear and to assess the subtle qualitative attributes of reproduced sound.

Active circuit — Describes a circuit containing transistors, ICs, tubes, and other devices that require power to operate, and which are capable of amplification.

Active loudspeaker or monitor — A loudspeaker system in which the input signal is passed to a line-level crossover. Its suitably filtered outputs feed two (or more) power amplifiers, each connected directly to its own drive unit. The line- level crossover and amplifiers are usually (but not always) built into the loudspeaker cabinet.

A/D [A-D] converter — A device which converts an analog audio signal into a digital representation.

AES — Acronym for Audio Engineering Society, one of the industry’s professional audio associations (www.aes.org).

Airy sound — The upper treble frequencies which sound light, delicate, open, and unrestricted in upper extension. A quality of reproduction systems that have very smooth and extended HF response.

Aliasing — When an analog signal is sampled for conversion into a digital data stream, the sampling frequency must be at least twice that of the highest frequency component of the input signal. Otherwise, the sampling process becomes inaccurate because there are insufficient points to define each cycle of the waveform, resulting in unwanted harmonic frequencies being added to the audible signal.

Ambience — The aurally perceived impression of an acoustical space, like the performing hall in which a recording was made.

Amp (Ampere) — Unit of electrical current (A).

Amp/amplifier — An electrical device that increases the voltage or power of an electrical signal. The amount of amplification can be specified as a multiplication factor (e.g. x10) or in decibels (e.g. 20dB).

Amplitude — The waveform signal level. It can refer to acoustic sound levels or electrical signal levels.

Analog — Analog circuitry uses a continually changing voltage or current to represent the audio signal. The electrical audio signal inside a piece of equipment can be thought of as ‘analogous’ to the original acoustic signal.

Attenuate — To reduce the signal amplitude or level.

Audio data compression — A system used to reduce the amount of data in an audio signal. Lossless audio data reduction systems (e.g. FLAC and ALAC) can fully and precisely reconstruct the original audio data with bit-accuracy, but the amount of data reduction is limited to 2:1. Lossy data audio reduction systems (e.g. MPEG, AAC, AC3, MP3, and others) permanently discard audio information that is deemed to have been “masked” by more prominent sounds. The original data can never be retrieved, but the reduction in total data can be considerable (12:1 is common).

Audio frequency — Signals in the range of human audio audibility. Nominally 20Hz to 20kHz.

Balanced wiring — Two conductors, each carrying an audio signal of the opposite phase for the purpose of lowering common mode noise. Identical (balanced) impedances are used to ground from each of two signal-carrying conductors, which are enclosed within an all-embracing shield. This shield is grounded (to catch and remove unwanted RFI), but it plays no part in passing the audio signal or providing its voltage reference. Instead, the two signal wires provide the reference voltage for each other— each signal is conveyed ‘differentially,’ and the receiver detects the voltage difference between the two signal wires and rejects anything in common such as noise.

Band-pass filter (BPF) — A filter that removes or attenuates frequencies above and below the center frequency at which it is set, and which only passes a specific range of frequencies.

Bandwidth — The range of frequencies passed by an electronic circuit such as an amplifier. The frequency range is usually measured at the points where the level drops by 3dB relative to the maximum.

Bass response — The frequency response of a loud‐ speaker system at the lower end of the spectrum. The physical size and design of a loudspeaker cabinet and the bass driver (woofer) determine the system’s low frequency extension (the lowest frequency the speaker can reproduce at normal level) and how quickly the signal level falls below that frequency.

Bit rate — The number of data bits replayed or transferred in a given period of time (normally one second). Normally expressed in terms of kb/s (kilobits per second) or Mb/s (megabits per second). For example, the bit rate of a standard CD is (2 channels x 16 bits per sample x 44.1 thou‐ sand samples per second) = 1411.2 kilobits/second. Popular MP3 file format bit rates range from 128kb/s to 320kb/s, while the Dolby Digital 5.1 surround soundtrack on a DVD-Video typically ranges between 384 and 448kb/s.

Blumlein array — A stereo-coincident microphone technique devised by English inventor Alan Blumlein in the early 1930s. It employs a pair of microphones with figure-eight polar patterns, mounted at 90 degrees to each other with the two diaphragms vertically aligned.

BNC — A type of bayonet-locking, two-terminal connector used for video and digital audio connections.

Boomy sound - Characterized by pronounced exaggeration of the midbass and, often, dominance of a narrow range of bass frequencies.

Buffer memory — A buffer is essentially a short-term data storage facility used to accommodate variable data read or write periods, temporarily storing data in sequence until it can be processed or transferred by or to some other part of the system.

Bypass test — Directly comparing the output signal from a device with the input signal being fed to it, by putting the device into and then out of the signal path and observing the difference.

Cabinet resonance — Any box-like construction will resonate at one or more frequencies. In the case of a loud‐ speaker, such resonances are undesirable because they obscure or interfere with the sound from the drive units. Cabinets are usually braced and damped internally to minimize resonance.

Capacitor — A passive, two-terminal electrical component which stores energy in the form of an electrostatic field. The terminals are attached to conductive plates which are separated by a non-conductive dielectric. Capacitance is measured in Farads. If a voltage is applied across the terminals of a capacitor, a static electric field develops across the dielectric, with a positive charge collecting on one plate and a negative charge on the other. When the applied voltage is an alternating signal, a capacitor can be thought of as a form of AC resistance that reduces with increasing signal frequency.

Cardioid — A specific form of polar response in a unidirectional microphone or loudspeaker. It has an inverted heart-shape with very low sensitivity at the back (180 degrees), but only slightly reduced sensitivity, typically between 3 and 6dB, at the sides (90/270 degrees).

Center fill — Correct image placement between the loudspeakers of sound sources which were originally located at or near center-stage.

Center stage — The part of the soundstage that is midway between the loudspeakers.

Chesty sound — A pronounced thickness or heaviness from reproduced male voice, due to excessive energy in the upper bass or lower midrange.

Chip — A slang term for an integrated circuit or IC.

Clinical sound — Pristinely clean but wholly uninvolving.

Clipping — When an audio signal is allowed to overload the system, clipping occurs and severe distortion results. The ‘clipping point’ is reached when the audio system can no longer accommodate the signal amplitude, whether because an analog signal’s voltage nears or exceeds the circuitry’s power supply voltage or because a digital sample amplitude exceeds the quantizer’s number range. In both cases, the result is that the signal peaks are “clipped” because the system can’t support the peak excursions— a sine wave source signal becomes more like a square wave. In an analog system, clipping produces strong harmonic distortion artifacts at frequencies above the fundamental.

Clocking — The process of controlling the sample rate of one digital device with an external clock signal derived from another device. In a conventional digital system, there can be only one master clock device, with everything else clocked or slaved from that master.

Close-miking —Placing a microphone very close to a sound source, normally with the intention of maximizing the wanted sound and minimizing any unwanted sound from other nearby sound sources or the room acoustics. In classical music circles, the technique is more often known as “accent miking. ”

Coincident — A means of arranging two or more directional microphone capsules such that they receive sound waves from all directions at exactly the same time. The varying sensitivity to sound arriving from different directions, due to the directional polar patterns, means that information about the directions of sound sources is captured in the form of level differences between the capsule outputs. Specific forms of coincident microphones include “XY” and “MS” configurations, as well as B-format and Ambisonic arrays. Coincident arrays are entirely mono-compatible because there are no timing differences between channels.

Coloration — A distortion of the natural timbre or frequency response of sound, usually but not always unwanted.

Comb Filtering — An undesirable series of deep filter notches created when a signal is combined with a delayed version of itself, causing a hollow coloration to the sound. The delay time (typically less than 10ms) determines the lowest frequency at which the filter notches start.

Common mode rejection — A measure of how well a balanced circuit rejects an interference signal that is common to both sides of the balanced connection.

Conductor — Any material that provides a low-resistance path for electrical current.

Copy protection — A method used by CD and software manufacturers to prevent unauthorized copying (DRM).

CPU — Central Processing Unit, the number-crunching heart of a computer or other data processor.

Crossover — A set of audio filters designed to restrict and control the range of input signal frequencies which are passed to each loudspeaker drive unit. A typical two-way speaker will employ three filters: a high-pass filter that allows only the higher frequencies to feed the tweeter, a low-pass filter that allows only the lower frequencies to feed the woofer, and a second high-pass filter that prevents subsonic signals from damaging the woofer.

Crossover frequency — The frequency at which one driver ceases to produce most of the sound and a second driver takes over. In the case of a two-way speaker, the cross‐ over frequency is usually between 1 and 3kHz.

Cut-off frequency — The frequency above or below which attenuation begins in a filter circuit.

Cycle — One complete vibration (from maximum peak through the negative peak, and back to the maximum again) of a sound source or its electrical equivalent. One cycle per second is expressed as 1 Hertz (Hz).

Damping — The control of a resonant device. In the context of reverberation, damping refers to the rate at which the reverberant energy is absorbed by the various surfaces in the environment. In the context of a loudspeaker it relates to the cabinet design and internal acoustic absorbers. Under‐ damping causes loose, heavy bass; overdamping yields very tight but lean bass.

Damping factor — The ratio of nominal loudspeaker impedance to the total impedance driving it (amplifier and speaker cable). In practice, damping is the ability of the amplifier to control speaker motion once the signal has stopped. A high damping factor means that the amplifier’s impedance can absorb the electricity generated by speaker coil motion, stopping the speaker’s vibration.

Dark sound — A warm, mellow, excessively rich quality in reproduced sound.

dB — The decibel is a method of expressing the ratio between two quantities in a logarithmic fashion, because the logarithmic nature matches the logarithmic character of the human sense of hearing. Decibels are used when comparing one signal level against another (such as the input and output levels of an amplifier or filter). When the two signal amplitudes are the same, the decibel value is 0dB. If one signal has twice the amplitude of the other the decibel value is +6dB, and if half the size it is -6dB.

dB/octave — A means of measuring the slope or steep‐ ness of a filter. The gentlest audio filter is typically 6dB/octave (also called a first-order slope). Higher values indicate sharper filter slopes. 24dB/octave (fourth order) is the steepest normally found in analog audio applications, though far steeper slopes can be achieved with digital filtering techniques through the use of DSP.

DC — Direct Current. The form of electrical current supplied by batteries and the power supplies inside electrical equipment. The current flows in one direction only.

Delicacy of sound — The reproduction of very subtle, faint details of musical sound, such as the sounds produced when a stringed instrument is plucked.

Depth of sound — The illusion of acoustical distance receding behind the loudspeaker plane, giving the impression of listening through the loudspeakers into the original performing space, rather than just listening to the speakers.

Detailed sound — The subtlest, most delicate parts of the original sound, which are easy to lose with the use of low- end equipment and cables.

Diffuse sound — Reproduction which is severely deficient in detail and imaging specificity; confused, muddled.

De-emphasis — A system which restores the spectral balance to correct for pre-emphasis.

Decay — The progressive reduction in amplitude of a sound or electrical signal over time, e.g. the reverb decay of a room.

Decca Tree — A form of ‘spaced microphone’ arrangement in which three microphone capsules (usually, but not always, with omnidirectional polar patterns) are placed in a large triangular array roughly two meters wide, with the central microphone one meter further forward. Sounds approaching from different directions arrive at each capsule at different times and with slightly different levels, and these timing and level differences are used to convey the directional information in the recording. The technique was developed in the early 1950s and was first commercially used in 1954 by Arthur Haddy and Roy Wallace. It was later refined by engineer Kenneth Ernest Wilkinson and his team at Decca Records, to provide a strong stereo image.

Digital Audio — A means of representing audio information in the form of binary codes comprised of strings of 1s and 0s, or their electrical or physical equivalents. Digital audio circuitry uses discrete voltages or currents to represent the audio signal at specific moments in time (samples). A properly engineered digital system has infinite resolution, the same as an analog system, but the audio bandwidth is restricted by the sample rate, and the signal-noise ratio (or dynamic range) is restricted by the word-length.

Direct coupling — A means of connecting two electrical circuits so that both AC and DC signals may be passed between them without need of a capacitor.

Dither — An intentionally applied form of noise used to randomize quantization errors used in processing digital audio data. It is often one of the last stages of mastering audio to a CD. Dither must be employed whenever the word length is reduced; otherwise quantizing distortion errors will occur.

Dolby noise reduction — Dolby is a manufacturer of analog and digital audio equipment in the fields of cinema and surround-sound equipment. Dolby’s noise-reduction systems included types B, C, and S for domestic and semi- professional machines, and types A and SR for professional machines. Recordings made using one of these systems must also be replayed through the same system. These systems vary in complexity and effectiveness, but essentially, they all employ the principles of spectral noise-masking in ever-more complex ways, using multiband encode/decode processing to raise low-level signals during recording while reversing the process during playback.

Dolby surround-sound — Dolby’s surround-sound systems started with an analogue 4:2:4 phase-matrix system with a very elaborate active-steering decoder called ProLogic, before moving into the digital realm with Dolby Digital, Dolby Digital Plus, Dolby True HD, and others.

DSD — Direct Stream Digital, invented by Sony and Philips for their introduction of the SACD. DSD uses pulse- density modulation encoding. The signal is stored as delta- sigma modulated digital audio, a sequence of single-bit values at a sampling rate of 2.8224 MHz (64 times the CD audio sampling rate of 44.1 kHz, but only at 1⁄32768 of its 16- bit resolution). Noise shaping occurs by use of the 64-times oversampled signal to reduce noise and distortion, caused by the inaccuracy of quantizing the audio signal to a single bit.

DSP — Digital Signal Processor. A powerful microchip used to process digital audio signals.

Dynamic range — The amplitude range, usually expressed in decibels, between the loudest signal that can be handled by a piece of equipment and the level at which small signals disappear into the noise floor.

Dynamics — A way of describing the relative levels within a piece of music.

Early reflections — The initial sound reflections from walls, floors, and ceilings following a sound created in an acoustically reflective environment.

Encode/decode — A system that modifies a signal prior to recording or transmission, then subsequently restores the signal on playback or reception.

Etched sound — Very crisp and sharply outlined, focused to an almost excessive degree.

Euphonic sound — Pleasing to the ear. In audio, “euphonic” has a connotation of exaggerated richness rather than literal accuracy.

Equalizer — A device which allows the user to adjust the tonality of a sound source by boosting or attenuating a specific range of frequencies. Equalizers are available in the form of shelf equalizers, parametric equalizers, and graphic equalizers—or as a combination of these basic forms.

Equivalent input noise — A means of describing the intrinsic electronic noise at the output of an amplifier in terms of an equivalent input noise, taking into account the amplifier’s gain.

Fat sound — The sonic effect of a moderate exaggeration of the mid- and upper-bass ranges. Excessively “warm.”

FET — Field Effect Transistor. A solid-state semiconductor device in which the current flowing between the source and drain terminals is controlled by the voltage on the gate terminal. The FET is a very high-impedance device with a warm and tube-like sonic characteristic when used in an audio circuit.

Fidelity — The accuracy or precision of a reproduced acoustic sound wave when compared to the electrical input signal.

Filter frequency — The “turnover” or “corner frequency of a high- or low-pass filter. Technically, the frequency at which the signal amplitude has been attenuated by 3dB.

Flash drive — A portable, large-capacity, solid-state memory stick configured to work like a conventional hard drive. Some computers and music servers are now available with solid state flash drives, SSDs, instead of normal internal hard drives.

Floppy disk — An obsolete computer disk format using a flexible magnetic medium encased in a protective plastic sleeve.

Flutter — A high-speed variation in replay speed causing rapid ‘fluttering’ pitch variations.

Focused sound — The quality of being clearly defined, with sharply outlined phantom images. Focus has also been described as the enhanced ability to hear the brief moments of silence between the musical impulses in reproduced sound.

Forward sound — A quality of reproduction which seems to place sound sources closer than they were recorded. Usually the result of a humped midrange, plus a narrow horizontal dispersion pattern from the loudspeaker.

Frequency range — A range of frequencies stated without level limits: e.g., the upper bass covers the frequency range 80-160Hz.

Frequency response — A range of frequencies stated with level limits. The uniformity with which a system or individual component sounds as if it reproduces the range of audible frequencies. Equal input levels at all frequencies should be reproduced by a system with subjectively equal output.

Fundamental — The lowest frequency component in a harmonically complex sound.

Gain — The amount by which a circuit amplifies a signal, normally noted in decibels.

Galvanic isolation — Electrical isolation between two circuits. A transformer provides galvanic isolation because there is no direct electrical connection between the primary and secondary windings; the audio signal is passed via magnetic coupling. An opto-coupler also provides galvanic isolation, as the signal is passed via light modulation.

Glare — An unpleasant quality of hardness or brightness, due to excessive low- or mid-treble energy.

Glassy sound — Very bright.

Golden sound — A euphonic coloration characterized by roundness, richness, sweetness, and liquidity.

Grainy sound — A moderate texturing of reproduced sound. The sonic equivalent of grain in a photograph. Coarser than dry but finer than gritty.

Gritty sound — A harsh, coarse-grained texturing of reproduced sound. The continuum of energy seems to be composed of discrete, sharp-edged particles.

Graphic equalizer — An equalizer with multiple narrow segments of the audio spectrum are controlled by individual cut/boost faders. The name came about because the fader positions provide a graphic representation of the EQ curve.

Ground — An alternative term for the electrical Earth or 0 volts reference. In electrical wiring, the ground cable is often physically connected to the planet’s surface via a long conductive metal spike. In an audio device, ground is often the chassis or the center tap of the power transformer.

Ground loop/ground loop hum — A condition created when two or more devices are interconnected in such a way that a loop of varying potential is created in the ground circuit. This can result in audible hums or buzzes in analog equipment or unreliability and audio glitches in digital equipment. Typically, a ground loop is created when two devices are connected together using one or more shielded audio cables, and both units are also plugged into the mains supply with safety ground connections via the mains’ plug earth pins. The loop exists between one mains plug, to the first device, through the audio cable shield to the second device, back to the mains supply via the second mains plug, and around to the first device via the building’s power wiring.

GUI — Graphical User Interface (pronounced “gooey”). In computer software, a GUI is a visual operating environment controlled by a mouse-driven pointer or something similar.

Hard disk drive — The conventional means of computer data storage: one or more metal disks (hard disks) hermetically sealed in an enclosure with integral drive electronics and interfacing. The disks are coated in a magnetic material and spun at high speed (typically 7200rpm for audio applications). A series of movable arms carrying miniature magnetic heads are arranged to move closely over the surface of the discs, to record (write) and replay (read) data.

Harmonic — High-frequency components of a complex waveform, where the harmonic frequency is an integer multiple of the fundamental.

Harmonic distortion — The addition of harmonics (multiple higher frequencies of the fundamental) that were not present in the original signal, caused by non-linearities in an electronic circuit or audio transducer.

Headroom — The available ‘safety margin’ in audio equipment required to accommodate unexpectedly loud audio transient signals. It is defined as the region between the nominal operating level (0VU) and the clipping point.

Height — Vertical directional cues which make some instruments sound as if they are above or below the other performers.

Hertz (Hz) — The standard measurement of frequency. 10Hz means ten complete cycles of a repeating waveform per second.

High-pass filter (HPF) — A filter which passes frequencies above its cut-off frequency but attenuates lower frequencies.

High-range (highs) — The upper portion of the audible frequency spectrum, typically denoting frequencies above about 1kHz.

High resolution — A digital format with long word- lengths and high sample rates, e.g. 24/96 or 24/192. Word- length defines the system’s signal-to-noise ratio and dynamic capabilities, while sample rate defines the maximum audio bandwidth possible.

Hiss — Noise caused by random electrical fluctuations (or by annoying a cat).

Hub — Normally used in the context of the USB– computer data interface. A hub is a device used to expand a single USB port into several, enabling the connection of multiple devices. Particularly useful where multiple software program authorization dongles must be connected to the computer.

Hum — Audio signal contamination caused by the addition of low frequencies, usually related to the mains power frequency.

Hysteresis — When the system’s output lags behind the input. Most commonly found in audio in the behavior of ferro-magnetic materials, such as in transformers and analog tape heads, or in electronic circuits such as “switch de-bouncing.”

IC — An abbreviation of Integrated Circuit, a collection of miniaturized transistors and other components on a single silicon wafer, designed to perform a specific function.

Imaging — The measure of a system’s ability to float stable and specific phantom images, reproducing the original sizes and locations of the instruments across the soundstage.

Impact — A quality of concussive force, as from a deep, strong bass attack, which produces a brief sensation of visceral pressure.

Impulse — An abrupt, extremely brief burst of signal energy; a transient.

Impedance — The “resistance” or opposition of a medium to a change of state, often encountered in the context of electrical connections (and the way signals of different frequencies are treated) or acoustic treatment (denoting the resistance it presents to air flow). Although measured in Ohms, the impedance of a reactive device such as a loudspeaker drive unit will usually vary with signal frequency and will be higher than the resistance when measured with a static DC voltage. Signal sources have an output impedance and destinations have an input impedance. In analog audio systems, the usual arrangement is to source from a very low impedance and feed a destination of a much higher impedance (typically 10 times as high).

Impulse response — An impulse response is the time- domain equivalent of the much more familiar frequency (and phase) responses in the frequency domain. A very brief click (technically, a Dirac delta function), which theoretically contains all frequencies at equal amplitude, is passed through the device being tested. The resulting output is the ‘impulse response’ of that device and uniquely describes its signal processing behavior. Impulse responses are very convenient for digital signal processing applications, as the source impulse is very similar to a single digital sample value.

Inductor — A magnetic reactive component that presents an increasing impedance with frequency. These are typically coils of wire used in speakers as low-pass filters, limiting high-frequency signals.

Infrasonic — Below the range of audible frequencies. Although inaudible, the infrasonic range from 15-20Hz can be felt if strongly reproduced.

Inner detail — The sonic subtleties within a complex program signal, reproducible only by a system having high resolution.

Input impedance — The input impedance of an electrical network is the “load: into which a power source delivers energy. In modern audio systems the input impedance is normally about ten times higher than the source impedance — a typical audio preamplifier or source component has an output impedance of 100 ohms, while input impedance is typically 10k ohms to 30k ohms.

Insulator — Any material that does not conduct electricity.

Intermittent — Something that happens occasionally and unpredictably, typically a fault condition in audio troubleshooting.

Intermodulation distortion — A form of non-linear distortion that introduces frequencies absent from and musically unrelated to the original signal. They are invariably based on the sum and difference products of the original frequencies.

I/O — The input/output connections of a system.

Isolator — A device intended to prevent the transmission of physical vibrations over a specific frequency range, such as a rubber or foam block. The term can also be applied to audio isolation transformers, used to provide galvanic isolation between the source and destination, thus avoiding ground loops.

Latency — The time delay experienced between a sound or control signal being generated and it being auditioned or taking effect, measured in seconds.

LED — Light Emitting Diode. A form of solid-state lamp.

LCD — Liquid Crystal Display.

Lean sound — Very slightly bass-shy. The effect of a slight bass rolloff below around 500Hz.

Lifeless sound — Sound that is dull, unfocused, unconvincing, and uninvolving.

LSB — Least Significant Byte (or bit). If a piece of data has to be conveyed as two bytes, one byte represents high-value numbers and the other low-value numbers, in much the same way as tens and ones function in the decimal system. The high-value, or most significant part of the message, is called the Most Significant Byte or MSB.

Linear — A device where the output is a direct multiple of the input, with no unwanted distortions.

Line-level — A nominal signal level which is around -10dBV for consumer audio and +4dBu for professional equipment.

Listening fatigue — A psychoacoustic phenomenon caused by prolonged listening to sound whose nature leans towards harsh, bright, or aggressive. The physical and psychological discomfort can induce headaches and nervous tension.

Low-pass filter (LPF) — A filter which passes frequencies below its cut-off frequency but attenuates higher frequencies.

Loudspeaker — A device used to convert an electrical audio signal into an acoustic sound wave. An accurate loud‐ speaker intended for critical sound auditioning purposes.

Loudness — The perceived volume of an audio signal.

Loudness wars — The practice of trying to make each new commercial music release sound subjectively louder than any previous release, based on the misguided notion that louder music is more exciting and results in more sales. A relationship between the average loudness of 45rpm singles and sales was noticed in America from jukebox plays, and that led to the first loudness war. However, the advent of the CD really ramped up the situation, with music being ever-more dynamically compressed to squeeze the average level higher and higher towards the 0dBFS peak level. This destructive trend is, thankfully, now being slowly reversed with the ubiquity of loudness normalization adopted by most online audio streaming services and broadcasters.