Summary
A cinema-equipment maker's guide to the hearing-impaired (assistive listening) and audio description channels in cinemas: where the audio comes from, how loops, radio and infrared carry it, and how receivers reach hearing aids.
Key findings
- Describes assistive listening audio, often called HI (hearing impaired), as generally a "dialog-centric" copy of the main audio with reduced dynamic range, carried to patrons by magnetic induction, radio or infrared. Cinema processors have long provided an HI output that mixes the left, centre and right channels, and many transmitters, including the maker's infrared emitters, compress it further.
- Says many digital cinema packages carry an HI track on track 7, but not all do, especially trailers, and pre-show and live content may not come in a package at all; "it appears the most reliable source of HI audio is the LCR mix provided by the cinema processor". Audio description (VI-N) usually comes on track 8.
- On loops in cinemas: one audio channel per auditorium, and possible interference from mains wiring and adjacent auditoriums. Because the one channel generally carries HI audio, audio description is generally restricted to radio and infrared.
- On radio: the signal does not stop at the auditorium walls, so a patron may choose the wrong channel and hear another auditorium's film; systems with few channels may have trouble reusing frequencies between auditoriums; and unencrypted radio audio can be intercepted outside, "possibly assisting in movie piracy".
- On infrared: an emitter on the rear wall or in the projector port is aimed at the screen so the signal reflects from it and other surfaces across the auditorium; it generally carries two channels (HI and audio description) and does not leave the room, so the patron cannot pick up the wrong auditorium.
- Says some hearing aids switch to the telecoil automatically in response to a telephone's static magnetic field, which loops and neckloops do not produce, so such aids get no audio from them unless they have a manual switch; headphones placed over the hearing aids give both fields and can switch the telecoil on. All receivers have the 1/8 inch mono jack the ADA requires, for neckloops or direct audio input.
- Lists ways to keep headphones sanitary: antibacterial wipes, replaceable ear pads, or patrons buying their own; the maker's 2.3 MHz infrared headphones also work with a consumer infrared TV headphone system.
- Compares its infrared system with Dolby's and Sony's radio-linked systems, listing 32 audio radio channels for Dolby's and 7 for Sony's and noting that infrared needs no channel reuse between auditoriums.
Limits
A maker's white paper that compares its own infrared system favourably with competitors' radio systems; it reports no measurements, user data or tests. Written for US cinemas under the ADA. The date is the last entry in the revision history (29 November 2017); the PDF was created on 29 December 2017.
Read the original
www.qscaudio.com/resource-files/whitepapers/q_wp_cin_accessibilitybestpractices.pdf
Cited in
Cite this source
Hallikainen H (QSC). QSC Accessibility Solutions Best Practices. QSC LLC (white paper). 29 November 2017. https://www.qscaudio.com/resource-files/whitepapers/q_wp_cin_accessibilitybestpractices.pdf (accessed 9 October 2026).
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