AC:- Acronym for Alternating Current, which is electrical current where electrical charge will travel in one direction, then change into moving in the opposite direction. When looked at through an oscilloscope, it's waveform is generally of a sinusoidal, square or sawtooth shape. Almost all domestic electricity found in homes is AC, with a frequency of 60 Hertz, Although virtually all electronic devices require DC power (batteries are DC) this is rectified through the use of transformers and rectifiers in the devices power supply. The reason why AC has been chosen as the standard for mains electricity when DC may be more suitable is due to it's abilty to be tranferred over great distances. See also DC and Rectifier.

AC Bias:- See "Bias".

A Cappella: - Music which consists only of voice or voices, and is bereft of any instrumental accompaniment.

Acoustics: - The study of sound and its behaviour within an environment.

A/D Conversion / Converter: - Analogue to Digital conversion. A converter is a piece of circuitry which acheives this. The quality of conversion is highly dependent on the amount of bits used in the conversion process, hence a 24 bit converter will acheive a much more accurate resolution of the sound than say, an 8 bit converter.

Additive Synthesis: - see Sound Synthesis .

"A.D.S.R.": - Attack, Decay, Sustain, Release. See also "synthesiser"/"envelope generator"

AES: - Acronym of the Audio Engineering Society.

After Touch: - facility of some keyboards which allows the sonic quality of a note to be altered by further pressure after the key has been initially depressed.

AIFF: - Digital sound format closely associated with Mac computer, but used on other platforms. Acronym of Audio Interchange File Format.

Algorithm: - Step by step solution to a mathematical problem. In software, a "routine" designed to realise some specific task.

Aliasing: - See Nyquist Theorem .

Alignment: - see "azimuth alignment".

Alignment Tape: - Tape using several specific tones, used for the optimisation of azimuth alignment (see below) on tape machines.

Ambience: - In audio / acoustic terminology, this is the reverberant quality of a room.

Ampere / Amp: - see Current.

Amplitude: - the level of a signal.

Analogue: - A continuous electrical signal whose amplitude varies with time.

Anechoic / Anechoic Chamber: - Anechoic means an absence of echo / reverberation. An Anechoic chamber is a room that has been acoustically designed to have no echo. Quite a hard thing to do, it is realised by the use of materials that will completely absorb sound waves, and is important for the testing of loudspeakers etc.

Arpeggio / Arpeggiator: - When the notes of a chord are played one after the other (sequentially), rather than all together (concurrently), this is an arpeggio. An Arpeggiator is a hardware device or software which will automatically create an arpeggio.

Attack: - In music, it is the period between the note being struck, and it's peak in terms of sound pressure level. It could be described as being a sounds initial transient.

Attenuate / Attenuation / Attenuator: - In sonic terms, this means reducing the level of something. An attenuator is a device which reduces the level of a signal.

Audio Frequency: - Frequency which falls within the range of human hearing, and measured in Hertz (20Hz - 20,000Hz) . See frequency for fuller explanation.

Autolocator: - Feature of some tape machines which enable a specific location on a tape to be stored, so that later, the tape machine may locate the same cue point.

Azimuth (alignment): - Degree of alignment between tape head and tape. Perfect azimuth alignment is when the tape head and the tape are both are making a perfect 100% contact with each other. When this is the case, alignment is said to be at it's "zenith", and it is exactly 90 degrees between the tape-head gap, and the longitudinal axis of the tape. Good azimuth alignment is vital to the sound quality produced by any kind of tape machine, with poor quality alignment, a tape machine will often sound muffled, and somewhat lacking in "top end". Poor azimuth alignment is largely responsible for the inferior sound quality produced by many cassette recorders.

Baffle: - The part of a loudspeker enclosure on to which the drive units are fastened. Alternatively, a sound absorbent barrier used in recording studios to separate musicians who are recording in the same room (sometimes referred to as a "gobo" in this sense). Hence a "well baffled speaker" is not a speaker that is in a state of some confusion! but rather, it is a loudspeaker which has been firmly fixed to a rigid base-board.

Balanced / Balanced Line: - An audio cable, most commonly a three pin "XLR" type mic cable, which has two conduction channels surrounded by metallic shielding where each conductor is of equal impedance relative to the ground/ earth. The conductors should have equal potential but opposite polarity. The advantage of this system is in terms of noise reduction, as a balanced line reduces unwanted noise because the opposing polarities ensures that unwanted noise is lost through "cancellation" when the inverted signal on one conductor is added to the original signal of the second conduction channel when the whole of the signal reaches it's destination.

Bandwidth: - Generally this is the amount of information which may be carried by a specific device, eg a modem may carry a maximum of x amount of bits per second, and that is said to be it's "bandwidth".

In music and sound, "bandwidth" may be the difference or "spread" between the lowest and highest frequencies that are capable of being produced by a piece of sonic circuitry (eg amplifier, computer soundcard etc) or musical intrument, where the "spread" between the frequencies corresponding to the lowest and highest notes would be regarded as the "bandwidth" of the instrument.

In a case of radio however, one could also speak in terms of the bandwidth that is capable of being received (as opposed to produced). This could be illustrated by saying that a radio that is capable of receiving signals within the bandwidth between 88 and 108 Mhz could be described as being an "F.M." radio.

Band Pass Filter: - A filter which allows only certain audio frequencies to pass, while rejecting all others above and below the cutoff points. An example of a bandpass filter may be found in a "3 - way" loudspeker system which will utilise a "woofer" for bass frequencies, a "midrange" unit for middle frequencies, and a "tweeter" for high frequencies. Whilst the woofer (which has no frequencies below it) will be able to have it's band of frequencies fed to it via a "low pass" filter and the "tweeter" which has no frequencies above it will have a high pass filter, the midrange, which will have frequencies both above and below it's area of operation will need to have its frequencies fed to it via a bandpass filter. See also "Crossover".

BJT: - Acronym of Bipolar Junction Transistor.

Bias: - Current / Voltage which determines the intrinsic "noise floor" of an audio device (measured in db's) ... Also AC bias (tape recorder) ... This is where bias is defined as an ultrasonic signal, which is usually found between the frequencies of 100/200 k Hz. This signal is incorporated with the conventional audio signal (via the record head) to reduce hysteresis induced harmonic distortion. The "bias" of a magnetic tape ("Metal", Chrome", "Normal" etc) refers to a bias signal which is roughly optimal to the kind of magnetic material that has been used in the manufacture of the tape. See "hysteresis" for more information.

Bi-Directional (microphone): - Microphone that will pick up sounds which are emanating from the front of the microphone (on-axis), and the rear of the microphone (off-axis), and largely reject those to the side. Also described as a "figure of eight" microphone, as the field pattern just described corresponds to that of the figure eight.

Binaural: - Hearing with two ears, humans who are not deaf in one / both ears hear things "binaurally".

Bit: - Smallest unit of digital currency, and the basis of the binary numbering system (bit is a shortening of "binary digit). A bit may be either 0 (off), or 1 (on). Eight bits make a Byte (see below).

"Boomy": - A subjective term used to describe sound recording - mix etc which has an excessive amount of bass.

"Break-Jack": - See Normalised / Normalled Connection.

Buffer: - A temporary storage location in memory, where data may be accumulated until it is ready for processing.

Bug: - Software error. A term that originally comes from the early days of computing, when a problem in an early military research computer was found to be caused by a moth inside the machine!

Bus: - In recording parlance, a bus is one of the main outputs of a mixer, which may be connected to one of inputs of a recorder, amplifier or signal processor. In computing parlance, it is the means by which data is transported between one part of a computer (eg Central Processing Unit) to another (eg Hard Disk). A computing type of bus may be separated into two parts, an address bus, and a data bus, and is measured in terms of its "width" in terms of bits (how many bits of data it can move at one time).

Buzz: - Annoying audio noise, created by harmonics at the 60 Hertz (the frequency of AC electricity) part of the sound frequency spectrum.

Byte: - A grouping of eight continuous bits, which are collectively known as a byte.

Capacitor / "Cap" / Condenser: - Electronic component which lets lets Alternating Currents through, but stops Direct Currents. Along with the transistor and the resistor, it is one the most common components in electronics.

Capstan: - slim roller on tape machine which along with a pinch roller, helps to maintain the correct tension of the tape relative to the tape head.

Cardioid: - see Polar Pattern.

Cent: - A musical cent is one hundredth of a semitone.

Chip: - Another word for an Integrated Circuit / Microprocessor.

Chromatic Scale: see scale.

Chorus: - Signal processing which creates an electronic simulation of a chorus by combining a signal with a delayed copy of itself. Often, the delay time and level of the copy is continuously varied in the interests of added "reality". This part of the process is known as flanging, often used as an effect in itself.

Circuit: - When electrical components (eg transistors, resistors, capacitors etc, are connected in a way that utilizes the central electrical / electronic concepts of current (see below), voltage, and resistance to perform some task, this is a circuit.

Circuit Board: - Convenient, flat layer on which the electronic components that make up a circuit may be placed, often containing metallic, conductive strips to connect the components together.

Clipping: - When the amplitude of a signal exceeds the maximum possible level of a device, the part of the waveform which is excessive is "clipped" resulting in a distortion of the sound. If clipping is harsh and prolonged, this can result in damage to the device in question. See also "Headroom".

Close Field: - See Near Field .

Coincident Pair: - If a pair of microphones are mounted together, so that the capsules are at a 45 degree degree angle (which is is the optimum position for picking up a nice two channel stereo sound field), then the two microphones in question could be described as being a " co-incident pair".

Complex Wave: - see Wave.

"Compression / Compressor": - see Dynamics Processing.

Concert Pitch: - See Pitch.

Condenser: - Old term for a Capacitor (see above).

Condenser Microphone: - Microphone which works on the principles of Capacitance and the Capacitor (see above). When the diaphragm of the capacitor vibrates in response to soundwaves, the Capacitor's ablity to hold charge varies. This measured change is the transduction of sound waves into electrictal signal. As the plates of the Capicitor need to be fed with charge everytime the mic is in use (an exeption to this is the "electret condenser" see below), an external source of power is required, usually a supply of up to 48 volts DC, which is also known as "phantom" power, as the power is carried throgh the same cable as the audio signal.

Condenser microphones offer the greatest fidelity in terms of tranducing soundwaves into an electrical signal, however, they do have the disadvatages mentioned above, as well as a great sensitivity to picking up hums/ ground loops etc, and a delicacy which renders many of them more suitable for studio, rather than stage use. Even then, many of them have to be used in conjunction with a special "cradle" which inhibits interference from external sources. However, there is no substitute for the fidelity and beauty of sound as rendered by a great "large - plate" condenser microphone.

Conductor / Conductive: - Any material which offers very low resistance to an electrical current passing through it. Opposite of insulator. Examples of good conductors include Gold, Silver, Copper and Aluminium. See also Ohm, Resistance Current etc. Also a musical term for someone who waves a stick at an orchestra.

CPU: - Acronym of Central Processing Unit aka microprocessor. See microprocessor for a full definition.

Crest Factor: - When the peak value of a signal is divided by its rms value, this is said to be its Crest Factor.

Crossover / Crossover network: - As most loudspeaker systems use two or more specialized drive units which individually only cover a part of the frequency spectrum ("woofer" for bass frequencies "tweeter" for treble etc), some kind of circuit is needed to separate the bands of frequencies which are appropriate for each of the drive units, this is a crossover. There are two primary ways of doing this.

Active Crossover: - One is to split the frequencies into different bands (bass, mid, treble etc) before the signal is amplified. This is known as an "Active" kind of crossover network. This "Active" way of splitting the frequency bands is usually used where multiple power amplifiers (eg one amp for bass, one for mid and so on) as well as multiple drive units are used. An example of this would be a large sound re-inforcement or "PA" system of the kind seen at large rock concerts etc, whose power output may be many thousands of watts.

Passive Crossover: - Most domestic "Hi Fi's" of lower power use what is known as a "Passive" crossover system, where the frequencies are split after the signal has been amplified.

High pass / Low pass / Band pass:

A high pass filter utilizes capacitors, as the impedance of a capacitor decreases for HIGH frequencies, this enables it to ensure the passage of higher frequencies, and stop the passage of more powerful, lower frequency signals which may blow the poor little tweeter unit to smithereens!

Conversely, a low pass filter utilizes an inductor or "coil", so called as basically it is a coil of wire of a certain length wrapped around a magnet. The "conversely" bit is that an inductor has a lower impedance for LOW frequencies, hence, it is useful as a low pass filter.

Use both a capicitor and inductor in parallel, and you have a band pass filter, rolling off frequencies both above and below the appropriate roll-off frequencies, and useful for speakers which utilize a "mid-range" unit.

Crosstalk: - When one electronic signal begins to interfere with another electronic signal, this interference is referred to as crosstalk.

Current: - A flow of electrical charge through a electronically conductive material. Usually measured in Ampere's (Amps A). 1 amp repesents 6.24 x 1018 "charge carriers", which are mostly electrons or electron deficient atoms.

Cutoff Frequency: - The frequency where the output of a filter, speaker etc is 3 Decibels per Volt lower than its maximum level. A loudspeakers / amplifiers / microphones frequency response is usually designated by this form of measurement.

Cycles Per Second: - See Frequency.

D/A Conversion / Converter: - Digital to Analogue conversion. A converter is a piece of circuitry which acheives this. The quality of conversion is highly dependent on the amount of bits used in the conversion process, hence a 24 bit converter will acheive a much more accurate resolution of the sound than say, an 8 bit converter. This aside a good "rule of thumb" for measuring the quality of D/A and A/D converters is to examine the S/N or "Signal to Noise" ratio of the device in question, which is measured in dBs.

D.A.T. - Acronym of Digital Audio Tape.

dbx: - Form of noise reduction patented by the dbx corporation of the United States. Works by compressing the sound during recording, and expanding it during playback.

DC: - Acronym for Direct Current, which is electrical current where the flow of electrical charge is ALWAYS in the same direction. Whilst almost all household elctricity is AC, the power produced by batteries is invariably DC. See also AC. When looked at through an oscilloscope, DC electricity produces a nice, even Sine Wave.

Decibel (dB): - A logarithmic measure of sound pressure level, a "Decibel" is one tenth of a "Bel". To put this in human terms, someone with pretty good hearing will be able to pick up sounds from @ 0 - 10dB (a quiet room can be as much as 40dB), and will start to feel pain and possibly sustain hearing damage if they are exposed to levels in excess of 135dB for any length of time (The public address speakers of the kind used at very large concerts may realize this if they are running at their maximum).

De-esser: - Signal processing device used to cut down on the sibilance or "hissy s's" which can sometime affect speech and singing through a microphone. This is usually through use of the techniques of high frequency compression combined with equalisation.

"Delay": - see Effects or "FX" Processing .

Detent: - A stop or catch. In electronics usually placed in a variable resistor such as a the middle point of a "pan" control on a mixing desk, to tell you where the "default" setting is.

Diatonic Scale: - See scale.

Digital: - The use of Binary data to represent information, "Binary" meaning that the highly complex data (audio, video, whatever) has been broken down into many values which have one of two states, positive and non positive. Positive is represented by 1, and non positve by 0. Each value is known as a "bit". For more on "Digital" within an audio context, see Sample.

Direct Injection (DI) Box: - Transfomer device which allows a musician to plug an an electronic instrument such as a guitar or bass, directly into one of the inputs of a mixing desk.

Directional Pattern: - see Polar Pattern.

"Dry" Signal: - Signal which is bereft of any processing, such as eq, gating, reverb and the like. Opposite of "wet" signal.

Dynamics Processing: - Processing which alters aspects of the dynamics (difference in sound level) of an audio signal. Common examples are...

"Compression": - ("squashing" the sound so that the difference between highest and lowest level of the sound is lessened. This usually means amplifying lower level signals, resulting in a sound that is perceived as louder and more "punchy"), the reverse of this is "expansion"...

"Noise Gating"(cutting the signal for very short periods of time when it falls below a certain level - useful as a form of noise reduction and occaisionally as an effect in itself).

Dynamic Microphone: - Microphone which works through a diaphragm being attached to a coil which operates within a strong magnetic field. The diaphragm vibrates in response to soundwaves, which, in turn stimulates motion of the coil. The magnetic field causes an electric current to flow through the coil, with a voltage which varies in sympathy with the motion of the diaphragm. This measured change is the transduction of sound waves into an electrical signal. Not as good in terms of fidelity as a condenser type of microphone, but more sturdy and less prone to noise interference, hence it's wide use on stage, or where a certain kind of "grittiness" is required.

Dynamic Range: - Difference in signal level between the loudest and quietest parts of a performance / recording etc. It is measured in decibels. Incidentally, the dynamic range of the human ear is said to be @ 130 dB.

Earth: - see ground.

Earth Loop: - see Ground Loop.

Echo: - Reflected sound that arrives at the ear of the listener after the direct sound. Not to be confused with reverberation, which is more of a gradual decay of a sound resulting from mixture of multiple echos, rather than a "bounce - back", where each echo may be heard distinctly.

Effects or "F.X." Processing: - Processing of audio signal in order to:

a) attempt to create a particular kind of acoustic environment or "atmosphere", or

b) make strange/funny sound effects!. Common examples include

"Reverb": - (device which simulates reverberation, which primarily changes our perception of the acoustic environment in which music is recorded or played), and

"Delay": - (device which will repeat sound at regular intervals producing echo-like effect).

c) attempt to replicate something eg a Chorus.

Effects return: - Connector, control, and/or path where a processed (wet) signal from an from a signal processing device enters a mixer. The enables the level of influence of the "wet" signal to be influenced via a potentiometer on the mixing desk.

Efficiency: - With loudspeakers, efficiency is generally the Sound Pressure Level (measured in Decibels) produced from a given watt of an amplifiers signal (dB's per Watt). A very efficient speaker can have a bigger influence on the SPL's produced by a system than the level of watts produced by the amplifier. A good rule of thumb is that a speaker that 3 dB's more efficiency per Watt that another speaker will be twice as efficient, and will be capable of producing the same amount of dB's from an amplifier with say, a 50 Watts power output, as the less efficient speaker would with an amp which has a hundred Watts power output. To put it another way if one speaker has an efficiency rating of 100 dB's per Watt, and another speaker has an efficiency of 103 dB's per Watt, the second speaker will not be @ 3% more efficient, it will be @ 100% more efficient!

Electret Condenser microphone: - Condenser microphone where the condenser / capsule is kept in a constant state of charge.

EMF (ElectroMotive Force): - See Voltage.

Envelope: - Factors which determine how a signal / sound changes over its period of existence. See also Sound Synthesis (envelope generator).

Envelope Generator: - see "Sound Synthesis" .

Error Correction / Error Detection: - Error detection is the process of determining whether any bits in a piece of digital audio have been lost. Error Correction is the process of replacing these lost bits.

Equalisation or "EQ": - Signal processing device which alters the frequency response of an audio signal. There are several types of equalisation, notable examples being "Graphic EQ" and "Parametric EQ". Equalisation may be used to help acheive the desired "flat" response in a performance / recording (perhaps to correct acoustic defincies in the local environment), or used to alter more un natural levels of frequency response as an effect in itself (modern djs / remixers tend to like doing this alot).

Event: - Any single piece of MIDI data is referred to as an "event", eg a note being triggered, the velocity of the note, a program change etc.

Expansion and Expander:- A form of Dynamics processing. When lower level signals are lowered (attenuated) and higher level signals are raised (boosted), this is expansion. A devise that acheives this through circuitry or software is called an expander. This is the opposite of compression.

Fader: - Sliding potentiometer which may increase or attenuate (the fade bit!) the gain of a signal. Usually associated with a mixing desk.

Fade-In / Fade-Out: - Gradually increment (fade in), or decrement (fade out) the level of a signal.

Fairlight: - Very early computer based music/ sampling workstation, developed in Australia through the mid/ late seventies by Peter Vogel and Kim Ryrie. It was relased in 1979 as the "Fairlight Computer Musical Instrument", it's most notable early users being Peter Gabriel and Stevie Wonder. Along with the American Synclavier, it went on to have a very significant impact on the music of the 1980's. Much more info here.

Feed: - In signal routing terms, this is where an output(s) from one device that is sent into the input of another.

Feedback: - When the sound being produced by the output signal (from a loudspeaker) is picked up by the input (in a kind of circular loop). When feedback reaches a certain level it causes an exponential rise in the level of certain frequencies, such as the screaming howl familar to guitarists and microphone users, or in the case of lower frequencies, a kind of ever increasing rumble.

FET: - Acronym of Field Effect Transistor.

Figure of Eight microphone: - see Polar Pattern.

Filter: - Electrical circuit designed to boost or attenuate certain frequencies within the sound spectrum.

Final Mix: - When a multitrack recording is mixed down into a two channel stereo recording (master).

Flanger / Flanging: - When a signal is combined with with a slightly delayed, modulated form of itself.

"Flat" (frequency) Response: - When an amplifier / microphone / loudspeaker displays an even frequency response (an even efficiency of frequencies within its bandwidth). This is usually defined as being within 2 dB's .

Frequency: – The amount of times that a wave repeats per second, measured in Hertz (which are cycles per second) after Heinrich R. Hertz the man who devised this form of measurement. Or to put it another way, if a soundwave vibrates the air x amount of times a second, this could be said to be it's frequency in Hertz. A young human who hasn't abused their ears (unlike most of the visitors to this site!) will be able to detect frequencies roughly in the range of 20 - 20,000 Hertz. However, as we get older and/or abuse our hearing listenting to loud music etc, this may gradually roll off so that an older person / Death-Metal fan may only be able sounds up to the frequency of say, 16,000 Hz. Our ears become progressively less sensitive to sounds below 500 Hertz, and they are at their most sensitive to sounds which have a frequency of @ 3-5kHz.

Frequency response: - Difference or "spread" between the lowest and highest frequencies that are capable of being produced by a piece of sonic circuitry (eg amplifier, computer soundcard loudspeaker etc).

Fundamental Frequency: - Nearly all sounds are made up of a Fundamental Frequency, which is the lowest frequency, and a collection of Harmonics, which are higher frequencies at stepped increments. It is the fundamental which gives us the the main frequency / pitch of the sound, and the interaction of the harmonics further up the frequency scale which gives us the essential "character" or "Tone Colour" of the sound.

Gain: - level of amplification of a given signal... Sound professionals tend to use this term where the layman may say "volume".

"Gain Riding": - The art of constantly adjusting the gain control of a mixing desk, amplifier etc in order to get the maximum possible level of amplitude (signal level) without going too far, and creating distortion though overload.

"Gang", "Ganged" etc: - In electronics, this is where two or more controls / sockets etc operate together, and changing one will automatically affect the other, as they are running in parallel.

Gap: - In tape recorders, the "gap" is the distance between the magnetic poles of the record, playback and erase heads.

"Gate": - see "Dynamics Processing" .

"General" MIDI (GM): - See MIDI .

Generation Loss: - A loss of sound quality between subsequent generations of an analogue recording (usually tape, where a copy of a copy of a copy may sound noticably inferior to the original recording). This is not a problem with digital recording, so long as it is not converted into analogue. This is due to the fact that in its most basic level, the copying of a digital recording is a copying of a vast amount of binary numbers, which can be checked.

Glide: - An effect where a note / pitch is decreased by a semitone, then "glides" its way back up to the original pitch.

Gobo: - See "Baffle".

Ground: - In electronics, this is a terminal which has no voltage, (known in the UK as "earth"). Both names arrive from the fact that the eventual end point of the ground / earth channel in an electrical system (eg mains electricity) is a conductive metal spike which must be in contact with the ground / earth, where any voltages are dissipated.

Ground / Earth Loop: - A condition which may occor in an electrical system where there is more than one Ground connection (see above), which causes a circulation, or looping of currents between ground points with cable resistance transforming this into fluctuations in voltage. Its symptom is a low hum @ 50 - 60 Hertz (see Frequency). If you are in the US it will be 60, in Europe 50.

"GS" MIDI : - See MIDI .

Guide Vocal: - When a vocalist records an initial vocal track for a multitrack recording which acts as a "guide" for other musicians who record their parts later. When the other tracks are recorded, this is usually then replaced with a "final vocal".

Half Step / Half Tone / 1/2 Tone etc: - American terms for a semitone.

Harmonic(s): - With the exeption of an electronically generated pure sine wave All of the sounds that we hear gain their essential "character" through the presence of harmonics, which are (in the case of music and audio) soundwaves whose frequency rises in incremental steps from a Fundamental frequency. To use an example, say there was a sound with a fundamental frequency (or if we were being musical, a note or pitch) of 100 Hertz. the "first" harmonic of this would have a frequency that was exactly double this (200Hz), the "second" would be double that (400) and so on. If this were a note, its pitch would corresond to the fundamental frequency of the sound, however the subtle interaction of these higher frequency harmonics of varying amplitudes (levels), will give the sound its "timbre" or "colour". Hence a guitar playing E4 will sound considerably different from a piano playing E4, although the fundamental frequency, or pitch will still be @ 329.63 Hertz (if they are correctly tuned!).

Harmony: - As all the musicians will know out there will probably know, harmonic concepts are the primary basis for the contruction of music theory, eg "chords" and the concept of playing music in a "key" are built around the notion of having a fundamental note, with a series of notes higher in pitch than this, their pitches being in harmony with the fundamental note, in line with the harmonic principles mentioned above.

Harmonic Distortion: - When harmonics are present in an output signal which weren't a part of the input signal of an audio device, this is referred to as harmonic distortion.

HDR: - Acronym of Hard Disk Recorder. Any digital audio recording device which is based on a computer type hard disk storage device, rather than D.A.T. (Digital Audio Tape), CD etc.

"Headroom:" - The difference in dB's or watts etc between the highest level of a sonic signal that is being produced, and the highest level that is capable of being produced without significant distortion/ spontaneous combustion! A sonic system always sounds at it's best when it has lots of headroom, and at its worst when there is no headroom at all, as clipping may result.

Hertz: - See Frequency .

High Pass Filter / HPF: - A filter which attenuates frequencies which are below it's stated cutoff frequency. See also "Crossover".

Hypercardioid: - see Polar Pattern (cardioid).

Hysteresis:- In a general sense, "hysteresis" can be explained by pressing on an object that yields, if when you release the pressure, the object doesn't quite spring back to the shape that it had before, then it is displaying hysteresis. In recording, this term is used mostly in relation to magnetic tape, and other devices which utilize magnetism (eg the magnetic fields of a microphone etc). With magnetic tape, it is when the magnetization of the tape lags slightly behind the electro-magnetic field produced from the recording head, creating a kind of distortion. This problem is partially overcome with the use of high frequency (around 100-200 k Hz) inaudible signal, which is known as an (AC) "bias"

Impedance: - At it most general electronic level, impedance is the amount of resistance and / or reactance offered by an electronic circuit or device to the (AC) current which flows through it. It is commonly represented by the mathematical symbol "Z", and is measured in Ohms. Some people may have had an unwelcome brush with the laws of impedance when (usually drunk at a party!) they attempt to wire several speakers to each channel of their amplifier, then witness the scene of expensive electronic carnage which usually follows!

Keeping with speakers and amplifiers, impedance in terms of Ohms is usually measured nominally (an average of the various levels of impedance measured throughout the scale of sound frequencies eg a typical loudspeaker with a nominal impedance of 8 Ohms may vary in impedance between 3 and 30 Ohms!) a speaker with a lower nominal impedance (say 4Ohms as opposed to 8) will offer less opposition to the power which the amplifier provides Amplifiers will also have a specifed minimum impedance rating, which is the lowest load (in terms of Ohms) that the amplifier is capable of driving. The lower the nominal impedance of the load, the higher the power (in terms of Watts) delivered to the speaker.

Returning to the "drunken party" scenario, if you connect a 4 speakers with a nominal impedance of 8 Ohms each to one channel of of your amplifier, collectively, they will have an nominal impedance load of 2Ohms, which is beyond the range of most domestic amps. However if it is capable of driving this load comfortably, the amp will deliver a much higher wattage than it would to an 8Ohm load. However finally, this must be qualified by reminding readers that nominal impedance is merely an average (see above), so some "margin of error" is required when matching speakers with an amp which may be operating at the limits of its impedance "envelope". So as they used to say in a famous TV cop programme "be careful out there!"

Infrasonic: - Sound frequencies which are below the lowest frequency of human hearing (20 Hz). See also Ultrasonic.

Insert Point: - A connection which permits the insertion of an external signal processing device (reverb, compressor, gate, eq etc) into the signal chain / path.

Insulator: - Any material which is very poor at conducting an electrical current (eg rubber, plastics etc). Opposite of "conductor". See also resistance.

Integrated Circuit (IC): - Originally conceived by UK Ministry of Defence scientist, Geoffrey Dummer an integrated circuit is a series of transistors (along with capacitors, resistors etc), working together to perform some task within one discrete unit. The first working model of an IC was patented by Jack Kilby of Texas Instruments as a "Solid Circuit" using Germanium as a semiconductor.

Slightly later (1961), a more advanced device, utilzing silicon as the semiconductive material, and known at the time as a "Unitary Circuit" (Later "Integrated"), was patented by Kenneth (Intel) Noyce when he was working at Fairchild Semiconductor. Intel's Ted Hoff later took IC's to an extreme, when he developed a device known as a "microprocessor", (the Intel 4044).

"IPS": - Acronym of Inches Per Second, a measurement of the speed that a tape travels when it is playing.

"IRQ" (Interrupt request): - An Interrupt Request is a message, usually sent from a hardware device within/ connected to your computer (eg Hard Disk, printer etc) via a dedicated line to the Central Processing Unit (CPU) of your system. In modern "plug and play" systems each dedicated IRQ line is automatically assigned a number, however in older systems this had to be set manually by the user. IBM standard PC's have a maximum of 15 IRQ lines, which work on a priority basis, depending on the relative importance of the Interrupt. so that an Interrupt Request with a high priority may interrupt one with a lower priority, and one with a very high priority may override both of them! For reference, heres a list (below) of the standard IRQ configuration for a PC standard computer.

00) - System Timer . . . 01) - Keyboard . . . 02) - Cascade Controller / 2nd PIC . . . 03) - COM's 2 & 4 . . . 04) - COM's 1 & 4 . . . 05) - Sound / Parallel Port 2 . . . 06) - Floppy Disk . . . 07) - Parallel Port 1 . . . 08) - Real Time Clock . . . 09) - Redirected IRQ2 / Network Available / Open . . . 10) - Open . . . 11) - SCSI / Video / Open . . . 12) - PS2 / Open . . . 13) - Co Processor . . . 14) - Primary Hard Disk (Master) / Hard Disk Controller / Open . . . 15) - Secondary Hard Disk (Slave) / Open .

It should be noted that IRQ's 00, 01, 02, 08 and 13 Should always remain static, and never be removed or shared with any other devices, whereas the others may possibly be reconfigured or removed.

Isopropyl Alcohol: - Best kind of alcohol to use for the cleaning of tape heads and other metallic devices used in audio.

"Jack" plug: - Very popular form of audio connector, available in stereo or mono formats. A full sized Jack plug has a spur of a quarter of an inch, but there are also smaller "mini" jack plugs.

Jitter: - A form of digital distortion caused by a very slight imprecision of digital sampling times (when sound is recoded digitally, it is done by "slicing" the signal into many segments, see Sample for a further explaination), leading to amplitude (signal level) errors. The distortion is more pronounced at the higher end of the frequency spectrum. Jitter also refers to timing errors where the word clock is an embedded part of the datastream (self-clocking).

k: - Prefix, an abbreviation of kilo or 1000, eg kiloHertz / kHz - 1000 Hertz, kiloByte / kB - 1000 bytes (oop's! sorry, that one's 1024 but you know what I mean!).

Key: - Foundation of all tonal music, a dominant note or chord of a piece of music, dominant major or minor scale used to construct melodies and harmonies in a piece of music. For example, a piece in the key of C major uses mostly notes of the C major scale. A piece of music can have several key changes in it, and this is known as "modulation" (see "key change" below).

The first note of a scale is known as the tonic and is the note that tells us the name of the key.

Key Signiture: - Usually found at the start of a musical manuscript, just after the clef. Saves the musician the bother of writing sharps or flats on every "accidental" note within the piece, and saves cluttering up the stave. If there are no symbols, then the piece will be in the key of C Major or A Minor, or it could possibly be a piece of arty "atonal" music by Karlheinz Stockhausen or someone similar, which has no key.

Key Change: Also known as "modulation".

Keygrouping: - see Sample (Multisampling).

Keying Input / Keying Signal: - A Keying Signal is an electronic signal sent to the Keying Input of an electronic musical or signal processing device which acts as a "trigger" to activate it.

Limiter: - Signal processing which sharply cuts off output once it reaches a certain preset level. Roughly it is a form of compression (see dynamics processing) with a very high ratio (10/1 or over) used mostly for for the protection of ears loudspeakers etc.

Line level signal: - For an audio device which uses unbalanced inputs / outputs, a line level signal is a signal with a level of -10dBV (0.316 volt). for a device which uses balanced inputs / outputs, it is a signal whose level is at +4dBm (1.23 volts).

Load (Computing): - Copy data from persistent storage (Hard Disk, Floppy etc) into RAM memory.

Load / Load Impedance: - Electronically, a load is burden placed in terms of resistance to the signal from an electronic circuit (eg loudspeaker / crossover from another circuit which is supplying the power (eg amp). The impedance is the measurement of this resistance in terms of Ohms.

Loop: - At its most basic, a loop is a series of instructions (computing) or beats / notes / chords (music) that is capable of constant repetition, consistently having the same result. Musically this will usually be a short piece measured in terms of a bar or more, which will seamlessly repeat without any musical / tempo inconsistencies, annoying clicks etc.

Low Pass Filter / LPF: - A filter which attenuates frequencies which are above it's stated cutoff frequency. See also "Crossover".

Machine Head: - The part of a guitar, usually situated at the top of the neck, which contains the tuning mechanisms for each string.

Major (music): - See Scale (Diatonic).

Master: - A device which controls another device, known as the slave. The final mix of a piece of music.

Microprocessor / CPU (Central Processing Unit): - Complex Integrated Circuit which is capable of performing some kind of computation / routine.

The three most important parts of a microprocessor are

a) it's Instruction Set (the instructions that the processor can execute).

b) It's Bandwidth (the number of bits it can process in a single instruction eg 8, 16, 32, 64 bit etc), and

c) It's Clock Speed, which is the amount of instructions that the processor can execute within one second. Hence, a 3GHz, 32 bit microprocessor can execute 3 billion cycles of 32 bits per second.

(Gordon) Moore's Law (also Intel) says roughly that an IC / microprocessor manufacturer will be able to place twice as many transistors into the same area of a microprocessor every eighteen months, with a coresponding increase in speed. Hence, if a companies fastest microprocessor clockspeed is say, 3.5 GHz, in eighteen months time it will be probably be around 7 GHz.

Microphone: - Electro-acoustic device which can pickup soundwaves and convert them into an electronic signal. See also Condenser Microphone, Dynamic Microphone, Polar Pattern etc

"MIDI": - Musical Instrument Digital Interface "protocol" launched 1982 which allowed electronic instruments to "talk" with each other digitally through three standardised ports which utilised the existing "DIN" standard connector: A network of musical instruments / effects etc may be created provided each instrument is compatible with this protocol. The ports are...

1) MIDI IN - Receives MIDI information from another device.

2) MIDI OUT - Transmits MIDI information to another device.

3) MIDI THRU - Allows data to pass through unaltered, which enables many instruments to be connected in series.

(see also "M.I.D.I. sequencing").

"General" MIDI (GM): - Standard set of sounds for use within MIDI system (MIDI keyboards MIDI compatable soundcards etc) which are designed to ensure compatibility for the playback of MIDI files. A sound set of 128 sounds is the standard.

"GS MIDI": - An extension to the General MIDI system (see above) created by the Roland corporation. Improvements over the standard GM include reverb / chorus effects, panning controls, and the capability of expanding the standard GM set of 128 sounds up to a maximum of over 16,000 !

MIDI Sequencer: - a piece of digital hardware/software that can instruct a compatible instrument to switch notes on/off at whatever velocity they were "recorded" at. Rather than recording sound or "audio" however it records the parameters of the note. The sounds triggered are dependent on the MIDI instrument or sampler supplying the sound. There are up to 16 channels per MIDI loop operating within increments of 0 - 127. M.I.D.I. instructions (e.g. turn note off, velocity etc), are known as "events".

MIDI + Audio Sequencer: - software running on modern microcomputers that takes advantage of modern processing power/storage capacity to run sequences of digitally recorded audio alongside the M.I.D.I. messages mentioned above.

XG (MIDI) : - An extension to the General MIDI system (see above) similar the Roland "GS" system with extra sounds, effects etc, only this system was developed by Yamaha, rather than Roland.

Minor (music): - See Scale (Diatonic).

Mixing: - Reduction and adjustment/enhancement of larger amount of independent audio signals into a smaller amount.

Modulation: - See Key Change.

Monophonic (Instrument/Synth): - Synthesiser (or other instrument) which is only capable of playing one note at a time. See also polyphonic.

Multisampling: - see "Sample".

Multi Timbral: - Capability for an electronic instrument to play more than one sound / patch at the same time. See also Timbre and Harmonic(s).

Multitrack Recording: - Ability to record and process several separate streams or "tracks" of audio, either together or at different times, to be played back as a synchronous whole, then probably "mixed down" to a stereo (two track) master for replay on ordinary systems.