Audio Visual Design Guidelines

Audio Replay systems and Public Address

153 views November 22, 2018 November 19, 2019 aetm 0

Intelligible audio is critical to the audience’s experience of any audio visual presentation. Spoken word and any programme audio must be clearly received by listeners, and the level and quality must be appropriate so listeners remain comfortable for the duration of each session.

Throughout the design process, attention must be paid to the different requirements of each output and key stakeholder group so the overall solution is adequate. For example:

  • Recording and conferencing systems may require a different mix of audio to any room PA system, and it may be delivered via a non-traditional interface such as USB
  • Hearing impaired listeners must be assisted to clearly discern the important audio over any background noise (minimum signal to noise ratio)
  • Any installed public address system must suit the physical acoustics of the room so listeners are not disadvantaged.

The skills required to commission an audio system are different to those required to program/configure the equipment, and technical managers should take care to ensure the build team includes an appropriate mix of ‘analogue’ and ‘digital’ skills and experience.



Term Definition
(Assistive) Listening System Technology describes in the building code as being compliant for hearing augmentation. May be induction loops, infra-red or radio frequency.
Decibel (dB) The decibel is a relative unit of measurement used widely in acoustics. It is a logarithmic unit describing the ratio between a measured level and a reference value. 

One common ratio to AV people is Sound Pressure Level (SPL). 

Weightings are applied to sound pressure scales to reflect the performance of the human ear under certain conditions. Most typically encountered are:

  • A-weighting: Covers the range 20Hz-20kHz at lower sound levels typical of our facilities
  • C-weighting: Used for high level measurements
Designer/AV designer The professional or technical specialist with responsibility for designing the electronic and electroacoustic (PA) systems and coordinating with other members of the design team. May be employed by the institution or an external consultant. 

AV designer may also have responsibility for leading electroacoustic scope, where briefed.

Digital Signal Processor (DSP) Any digital techniques for the manipulation of an electrical system.

In installed sound systems the term is often shorthand for the subset or equipment which performs audio acquisition, processing and routing.

EWIS Emergency Warning and Intercom Systems; one common form of warning system for fire and other emergency events.
Hearing augmentation The communication of information for people who are Deaf or hearing impaired by using a combination of audio, visual, and tactile means. (AS1428.5)

As well as assistive listening systems, can include warning lights, sign language and other non-AV provisions.

Intelligibility Speech intelligibility is a rating of the proportion of speech that is understood.
Signal to noise ratio The difference between the measured sound level and the noise floor (all other sources). Expressed in dB.
STI The Speech Transmission Index (STI) is an objective metric ranging between 0 and 1 representing the transmission quality of speech with respect to intelligibility by a speech transmission channel

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