Knowledgebase

Foldback

Foldback is a feed of audio to the studio, via either loudspeaker, headphone or earpiece (IEM). It may be to provide the presenter and/or performers with a Cue feed from an external source or from a singer’s Microphone, to reinforce a singer’s voice for confidence or as an aid to tuning, or to provide actors…

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Induction Loop

An Induction Loop or Audio Frequency Induction Loop System (AFILS) is a system commonly used by hearing aid users to clearly hear the sound in a theatre, through the bandit-proof glass screens in a bank or just a telephone call. It can also be used to provide wireless talkback or IEM to crew or presenters…

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Bright Eyes (Phantom checker)

This “Bright Eyes” device was described by Hugh Robjohns in this Line Up article (June/July 2006) and uses a circuit designed by Chris Woolf. A Bright Eyes can be a very useful tool to have during rigging or fault finding to check if an XLR cable has active microphone powering. It is simple to construct…

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Sabin

A Sabin is the amount of absorption equivalent to one square metre of open window (which would allow the sound to escape from the room with no reflections). Named after American acoustician Wallace Clement Sabine (June 13, 1868 – January 10, 1919).  See also Sound Absorption Coefficients for Some Common Materials.

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Decibel (dB)

The human ear does not react to changes in sound in a simple, linear way. To double the loudness of a sound, say by turning up the volume control on an audio amplifier, most people find that they need to increase the power produced by the loudspeaker by about ten times. If we were to…

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Optimising Windows or Mac computers for audio

Problems are usually bus and/or buffer overload. As Macs and PCs now share the same Intel chipsets, hopefully the “rules” that you have to apply to optimise a PC for audio will be similar. Basically the machine needs to be focussed entirely on handling audio and minimising system interrupts on its data buses. While the…

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Electromagnetic Spectrum

The Electromagnetic Spectrum is the range of all possible frequencies of electromagnetic radiation. See the excellent diagram reproduced by kind permission of Louis Keiner http://www.keiner.us/. The sections of particular interest to IPS members are usually referred to as the Radio Spectrum (although they are mostly used for television!), and are: Low Frequency (LF) covers frequencies…

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Electret wiring

Electret personal microphones are all unbalanced. They all need a screen, both for the cable and for the grille and casing around the capsule. This usually gets connected to 0V. The electronics inside the capsule will have two external connections. One connection always needs to be kept more +ve than the other but it makes…

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After Fader Listen (AFL)

AFL may be After-Fader Listen or After-Fader Level, depending on whether the user is more concerned with the quality and/or content of the signal or with its level. It is similar in operation to Pre-Fader Listen (PFL) except that the signal is derived after the channel fader instead of before. As AFL is also derived…

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Audio software

This is a selection of computer software for audio applications which is either free or inexpensive. It has been compiled from various sources, and inclusion in this listing does not in any way imply any endorsement by the IPS, or any warranty that it will be satisfactory. User (and buyer) beware! Contents 1 PC Software…

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Edit Decision List (EDL)

An Edit Decision List (EDL) is simply an ordered list of items of recorded video and audio with Timecode references which enables a video editor to assemble a version of the final programme.

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iXML

The iXML specification is designed to provide an unambiguous communication of file and project based metadata between various stages of workflow in production, telecine, picture editorial and audio post production. iXML is primarily designed to be used as a  RIFF (embedded tagged data) chunk inside a Broadcast Wave file (although it can be optionally included…

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Metadata

Metadata is literally data about data. In its simplest form it could be a note attached to an item of recording medium (e.g. a tape or disc) telling the user what is on the medium, how long it is and where and when it was recorded. More practically it will be digital information embedded in…

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Audio levels

Analogue audio signal levels have historically been categorised for professional usage in two groups – microphone level (low) and line level (high). Domestic equipment generally falls into a third category, just below professional line level. Signal levels are measured using units based on the Decibel. There are many different types of Level Meter used for…

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Noisy floors

Noisy Floors can be the bane of a Sound Recordists life. There are two main problems; noise from things like heels hitting a hard and hollow floor and noise from the floor itself as objects move over the surface. Heels and Legs High heels and chair legs can easily produce enough noise to drown out…

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Phantom Power

Phantom Power is a means of powering condenser microphones remotely, using balanced microphone cable. The AES (and IEC 61938) endorses two voltage levels, 48 V and 12 V, and they are referred to as P48 and P12

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Stereo

Stereo, short for Stereophonic, is a system of sound recording and reproduction which uses two synchronised channels, usually referred to as A (left) and B (right). There are several conventions for colour-coding analogue signals; the BBC adopted the nautical convention of Red for Port (Left) and Green for Starboard (Right), which can be confusing when…

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Balanced line

Balanced lines are typically – and quite incorrectly – explained as follows. A signal is split into two equal but antiphase parts in a balanced line driver. These signals are connected to each leg of a pair cable and eventually arrive at a balanced receiver. This device inverts one leg of the signal. In doing…

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Boom

Boom is defined in the Concise Oxford English Dictionary as “a movable arm carrying a microphone or film camera” and in Collins Concise as “a pole carrying an overhead microphone and projected over a film or television set“. In sound studios a boom is either an arm fixed to a floor-mounted microphone stand or a…

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Tonader Power (T power)

Tonader Power, T Power, T12 or AB Power all refer to a method of powering microphones via their cable. This system uses 180 ohm feed resistors and a 12V supply but does not send the DC power as a common mode signal like Phantom Power. The powering is unbalanced and shares the same path as…

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Critical Distance

Critical Distance or Dc is the distance from a sound source where the level of direct sound equals that of any reverberant sound. Dc applies to all sound gathering but measuring it is normally only required when advance planning of microphone positions is needed. Critical Distance does not dictate where a microphone must be placed…

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Broadcast Wave Format (wav)

Broadcast Wave Format was developed by an EBU Project Group (see The Broadcast Wave Format – an Introduction) to provide a product-independent means of exchanging programme material between workstations from different manufacturers. It is based on the Microsoft WAVE audio file format (file extension .wav), which is one of a number of file types specified…

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Watts

Watts are a measure of power. The symbol is W (never w). Electrically Watts = Amps x Volts. The name derives from Scottish engineer and inventor James Watt (1736 – 1819) in honour of his work that transformed the primitive steam engine into a practical power unit. Watts are obviously useful for indicating the power…

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Connectors

Contents 1 Sex 2 XLR 2.1 3 pin 2.2 4 pin 2.3 5 pin 2.4 6 pin 2.5 7 pin 3 Jack 3.1 ‘A’ gauge 3.2 ‘B’ gauge 3.3 MIL-plug 3.4 Bantam 3.5 3.5mm 3.6 2.5mm 4 Hirose 4.1 4 pin 4.2 10 pin 5 Tajimi 5.1 12 pin 6 DIN 6.1 2 pin 6.2…

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RMS

An acronym for Root Mean Square, a mathematical means of calculating the average level of a varying audio signal for the purposes of metering or estimating the power of, for example, loudspeaker amplifiers.

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EBU

The European Broadcasting Union or EBU was formed on 12 February 1950 by 23 broadcasting organisations from Europe and the Mediterranean. Members are radio and television companies, most of which are government-owned public service broadcasters or privately owned stations with public missions. In 2007 the EBU has 74 active members from 55 countries, and 43…

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Jackfield

Most mixers, except for portable types, have an associated Jackfield, also known as a Patchbay, either integral with the mixer frame or fitted nearby in a wall-mounted rack or free-standing console. The jackfield is used to terminate incoming lines from remote studios, tape machines etc and to provide access to the mixer line inputs and…

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Background Noise

Background Noise are sounds that are not the main sound you want to record. Sounds from traffic outside, air conditioning, lighting and so on. Ideally sources of background noise are stopped, switched off or removed but what do you do if you had no choice but record the noise? Record an atmos/room tone Wild Track…

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Timecode

Timecode in audio operations refers to the SMPTE/EBU time and control code which is used for synchronising audio with video and for locating sections of programmes. Linear Time Code (LTC) is most commonly used, although Vertical Interval Timecode (VITC) may be encountered in television operations. Both versions use an 80-bit binary code to identify video…

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Direct Current (DC)

Direct Current or DC refers to the unidirectional flow of electrons from high to low potential, as opposed to Alternating Current or AC where the flow regularly reverses in direction at a specific frequency. By convention this flow is considered to be from positive to relatively negative points; note that this direction is not the…

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Word Clock

Taken from Annex B of AES11. “AES recommended practice for digital audio engineering – Synchronization of digital audio equipment in studio operations” Annex B (Informative) Word Clock It is possible to meet all the timing requirements of AES11 by means of a square wave at sampling frequency basic rate, commonly called word clock. It is…

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Aircraft PTC

Advice/Tips on getting good sound for aircraft PTCs (Piece to Camera) The general advice here is to get your microphone as close as possible to the presenter’s mouth. A common technique is to attach your personal mic to the aviation boom but on the opposite side to the mouth as this helps shield the microphone…

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Pan Pot

Panpot is an abbreviation of Panoramic Potentiometer, a device used in Stereo mixers to vary the signal levels sent to the outputs from a Mono input, and thus apparently move the sound across the “sound stage” between left and right.

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Sound Levels

Sound Pressure Levels Our ears respond to fluctuations in the steady atmospheric pressure, so when measuring sound, that is what we usually measure. Sound pressure levels (or Sound Levels for short) are specified in Decibels, relative to a reference pressure of 20 micropascals. This reference pressure of 20 micropascals is nominally equal to the threshold…

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BLITS (Black & Lane’s Ident Tones for Surround)

Black and Lane’s Ident Tones for Surround (BLITS) developed by Sky Television Sound Supervisors Martin Black and Keith Lane in 2005/6 to provide a standardised form of channel identification and alignment for surround sound material. BLITS is a broadcast-specific line up tone system for use with 5.1 surround sound formats, and is currently being considered…

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Interference Tube

An Interference Tube is simply a long metal tube with a series of circumferential slots cut into it, fitted onto a directional Microphone. These slots produce interference patterns in sound waves from the sides, resulting in partial cancellation of off-axis sounds and a resultant apparent increase in the gain of sounds from directly in front.

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Super Audio CD (SACD)

Super Audio CD (SACD) launched by Sony in 1999 and intended to supersede the original Sony/Philips CD.

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Automated Dialog Replacement (ADR)

Automated Dialog Replacement (ADR) was used by the Magnatech Corp as a marketing phrase (mid 1960s). Magnatech made the system which comprised the projector, the recorder and the control box. It enabled record drop-ins and -outs across 3 tracks (3 attempts) to be programmed to the footage counter, and the whole reel of 10 minutes…

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Off Tube

“Off Tube” is when commentary for an event is provided by the commentary team just watching the televised pictures. While commentators almost always have a picture monitor (or “tube”) regardless of their location, there is great advantage to be had from also being in a position to see the proceedings with their own eyes, and…

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Volts

Volts (symbol V – not v) measure the electrical pressure, or potential difference available to force current through a circuit. The name derives from the Italian physicist Alessandro Volta (1745–1827), who invented the voltaic pile, the first chemical battery. Voltages can have a fixed polarity (Direct Current volts), or can change more or less cyclically…

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Creative Commons Licence

A Creative Commons Licence allows authors, artists, and educators to mark their creative work with the freedoms they want it to carry, changing the default of “All Rights Reserved” into “Some Rights Reserved”, as the creator chooses. There are three areas that the licence covers; attribution, commercial use and derivatives. These can be combined in…

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Pressure Zone Microphone (PZM)

Pressure Zone Microphone is a registered trade mark of Crown International, and describes a method of mounting a microphone close to a flat surface to minimise room acoustics. Other variants are described as Boundary Microphones. See http://www.uneeda-audio.com/pzm/

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Cue

A “Cue” may be visual or aural. In television it is usual for somebody in the studio to be given a visual cue to begin by a wave from the Floor Manager, and also sometimes to conclude by “winding up” gestures (which become more frantic as time runs out!). In radio a cue light is…

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Diary Services and Agents

First of all to quash a big misnomer. A Diary Service is not there in order to ‘get you work’. That is what an Agent does. Now – to more detailed thoughts. When looking at Diary Services it might be wise to take a brief look at how they emerged and why. In the late…

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Impedance

Electrical impedance is effectively resistance in an AC circuit (see Ohms). Impedances are significantly more complicated than simple resistance because they are frequency conscious and because they can apply to the behaviour of an entire circuit rather than a single element. There are load impedances, having the effect of a virtual resistor across the input…

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Underwater sound

A member asked on IBSNET for advice on hydrophones. Chris Woolf responded:- Hydrophones vary quite a bit in quality from high grade phantom powered  devices to some pretty poor plug-in power versions. The are invariably omnis and since the propagation of sound in water is very different to air you can expect a lot of LF…

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Late Payment

Running a business, owed money from another business? Then you have a statutory right to interest and compensation under the Late Payment of Commercial Debts (Interest) Act 1998 (as amended). There is no obligation to charge interest or claim compensation on a late payment, you just have a legal right to do so. Be aware…

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Talkback

Talkback originated in radio studios, where staff in the control cubicle who could hear the presenters and performers on their monitor loudspeaker were able to communicate with them using a dedicated microphone/loudspeaker system, “talking back” to the studio. This system was extended by the introduction of “reverse talkback” which provided the presenter with an additional…

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Polar Pattern

The Polar Pattern of a Microphone describes its directional sensitivity. The main family of patterns is a continuous spectrum between omni and bi-directional (figure-of-eight). Thus their titles are somewhat arbitrary, often overlap and, perversely, in most cases they are best defined by their ability to reject sound. Polar Patterns are generalised – they give an…

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Aircraft Intercom

While it is possible to connect to Aircraft Intercom systems, the quality is at communications level rather than broadcast, though it may be adequate for short items and can give a useful “atmos”. Aside from the issues of obtaining the correct connector you MUST obtain permission from the pilot on each occasion before connecting location…

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