Glossary

Direct Injection, or Direct Instrument Box. A device which accepts the signal input from a guitar, bass, or keyboard and conditions it to conform to the requirements of a microphone signal at the output. The output is a mic-level, balanced signal with a low source impedance, capable of driving long mic cables. There is usually a facility to break the ground continuity between mic cable and source to avoid unwanted ground loop noises. Both active and passive versions are available, the former requiring power from internal batteries or phantom power via the mic cable. Active DI boxes generally have higher input impedances than passive types and are generally considered to sound better.

the movable membrane in a microphone capsule which responds mechanically to variations in the pressure or pressure gradient of sound waves. The mechanical diaphragm vibrations are converted into an electrical signal usually through electromagnetic or electrostatic techniques such as ribbon, moving coil, capacitor or electret devices.

Diffusion is the spreading of sound energy within an acoustic environment. It the context of acoustic treatment diffusion can be thought of as the opposite of absorbtion, and a range of diffusion panels and surfaces are available which are designed to reflect incident sound back into the room in various ways.

A form of acoustic panel employed in the acoustic treatment of a room which reflects incident sound in specific ways with the aim of maintaining an even spread of sound energy withint he environment. (More)

A means of representing information (eg audio or video signals) in the form of binary codes comprising 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 analogue 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. (cf. Analogue)

A digital processor that generates delay and echo effects.

A digital processor which simulates acoustic reverberation.

A consumer multi-pin connection format used for vintage microphones, some consumer audio equipment, and MIDI cabling. Various pin configurations are available.

A form of audio compressor which uses a diode-bridge (sometimes known as a diode-ring) arrangement as the variable gain-reducing element. The design was popular in the 1960s as it provided faster responses than typical opto-compressors, and less distortion than many FET designs. However, noise can be an issue as the audio signal has to be attenuated heavily before the diode-bridge, and considerable (~40dB) gain added subsequently. The diodes also need to be closely matched to maintain low distortion.

A means of connecting two electrical circuits so that both AC and DC signals may be passed between them.

Used to describe vinyl discs, CDs and MiniDiscs.

An abbreviation of Diskette, but now used to describe computer floppy, hard and removable data storage disks.

Some form of corruption — wanted or unwanted — of the source signal. All forms of distortion are formed by non-linearities in an electronic circuit or an audio transducer. Harmonic Distortion is typically caused by over-loading to some degree components in the signal pathi, resulting in the addition or stengthening of odd and/or even harmonics of fundamental frequencies present in the source signal. Anharmonic distortion involves the introduction of frequencies not musically related to the source signal, usually through some form of modulation process, such as aliasing in overloaded digital equipment, or scrape flutter in analogue tape machines. Some forms of distortion are often added intentionally to a musical source to alter it's character in a pleasing way — such as on an electric guitar, for example. 

A system whereby low-level noise equivalent to one quantising level is combined with a digitised audio signal in such a way as to perfectly linearise the digital system. Dither must be employed whenever the wordlength is reduced, otherwise quantising distortion errors will manifest.

Direct Memory Access. Part of a computer operating system that allows peripheral devices to communicate directly with the computer memory without going via the central processor (CPU).

A versatile form of surround sound technology, more commonly referred to as 'immersive sound´, developed and marketed by Dolby Labs and introduced in 2012 with the Disney/Pixar film, Brave. While mostly employed for film and television content, it is increasingly being used in music productions, identified as 'Dolby Atmos Music'. DTS:X is a broadly similar rival technology.

The most obvious improvement compared to conventional 5.1 and 7.1 surround sound formats is that Dolby Atmos adds height channels — speakers in the ceiling — which greatly enhances the sensation of being enveloped with sound, hence the 'immersive' moniker. However, the underlying technology is also considerably more advanced as it combines conventional (static) channels of surround sound with 'object-based' audio content which can be directed to any speaker (or to move between speakers) by metadata encoded with the audio. It is this feature which provides the content creators with enormous flexibility over where individual sounds are placed and moved within the mix, in addition to a conventional 'bed' of surround sound.

Moreover, Dolby Atmos decoders are designed to map the source audio content dynamically to the connected sound system accommodating virtually any number and layout of loudspeakers, or even just to stereo earphones, maintaining the best possible impressive of the intended immersive sound stage (using binaural encoding in the case of stereo earphones).

Invented by Bang & Olufsen and licensed to Dolby. HX (often marketed as HX Pro) stands for 'Headroom eXtension' and it is a record-processing system used on some analogue open-reel and cassette tape-recorders (there is no complementary replay processing). Dolby HX Pro varies the amount of recording bias depending on the strength of high-frequencies in the audio signal itself to avoid magnetic saturation and over-biasing. This makes it possible to record with a higher overall fluxivity on the tape.

A manufacturer of analogue and digital audio equipment in the fields of tape noise-reduction systems and cinema and domestic 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 via the same system. These systems varied in complexity and effectiveness, but essentially they all employed the principlals 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’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.

A specific shape of drive unit diaphragm intended to push and pull the air to create acoustic sound waves. Most tweeters use dome-shaped diaphragms which are driven around the circumference by the drive unit’s motor system. ‘Soft-domes’ are made of a fabric - often silk - while metal domes are constructed from a light metal like aluminium, or some form of metal alloy.

Disk Operating System. Part of the operating system of PC and PC compatible computers

A method for removing or attenuating the noise component of a recording or transmission system, in which the signal is pre-conditioned in a specific way which is reversed on playback. Most analogue noise-reduction systems are of the double-ended type, such as the Dolby and DBX systems.

Also known as a Reussen screen. The signal-carrying wires in a microphone cable are protected from external electrostatic and RF interference by a ‘screen’ which is a surrounding conductor connected to earth or ground. The Reussen screen is a specific form of cable screen, comprising two overlapping and counter-wound layers which are unlikely to ‘open up’ if the cable is bent, yet remain highly flexible

A physical device designed to generate an acoustic sound wave in response to an electrical input signal. Drive units can be designed to reproduce almost the full audio spectrum, but most are optimised to reproduce a restricted portion, such as a bass unit (woofer) or high-frequency unit (tweeter). A range of technologies are employed, with most being moving-coil units, but ribbon and electrostatic drive units also exist, each with a different balance of advantages and disadvantages. Also known as a ‘driver’.

A piece of software that handles communications between the main program and a hardware peripheral, such as a soundcard, printer or scanner. Also a term used to refer to a physical loudspeaker drive unit - eg bass driver.

A sudden brief loss of signal level. In analogue recording tape this is often caused by a defect in the oxide layer caused by damage (eg. creasing) or by a temporary clogging of the replay head, and typically affects the high-frequencies most. The effect is less likely and less noticable with wider and faster tape formats.

- See Isolation Room

A synthetic playing surface which produces electronic trigger signals in response to being hit with drum sticks.

A signal that has had no effects added.

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

The practice of transferring material from one medium to another, or of adding further material to an existing recording (cf. Over-Dub).

A system for controlling the level of one audio signal with another. For example, in a broadcast radio context a music track can be made to 'duck' or reduce in volume whenever there's a voice over.

A 'Dummy Head' is a binaural recording array which intentionally resembles (to a greater or lesser degree) the size and shape (and sometimes also the density) of the average human head, with two microphones placed on opposite sides in the positions of the ear canals. The idea is to capture passing sound waves in the sa,e way as a normal listener would perceive them, with the correct inter-aural time delays and head shadowing effects which are critical to assessing directional cues.

To transfer digital data from one device to another. A SysEx dump is a means of transmitting information about a particular instrument or module over MIDI, and may be used to store sound patches, parameter settings and so on.

The ability to play two notes at once. Some dual-oscillator mono-synths allow the keyboard to generate two control voltages (from the lowest and highest keys played) which are routed to separate oscillators allowing two notes to be played simultaneously (see Paraphonic). For example, the ARP Odyssey and the Moog Subsequent are both duophonic synths.

'Digital Vinyl System' is a way of controlling and manipulating the playback of digital audio files in a computer by using conventional analogue turntables as the interface, thus maintaining a traditional 'disk-jockey' style of hands-on 'turntablism' control, including scratching. The system is based upon using special vinyl discs which carry standard timecode signals. The output of the vinyl replay chain is routed into the computer via an audio interface in the usual way, and the software is then able to analyse the timecode to determine changes in playback speed, direction, and position of the pickup on the vinyl disc, and apply that timing and speed information to the reproduction of a digital audio file. Some latency is inevitable in such a system, but it is usually very short.