25CSS WG on Cinema B-Chain Characteristics and Expectations

Viewing Projects Group Assignment
last updated: 2019-10-14
contact: Brian Vessa



Create recommended practices and engineering guidelines for cinema sound systems to ensure they faithfully play back modern, digital, full dynamic-range movie soundtracks.

Progress Report

Project Proposal

Project Type

SMPTE Engineering Project (ANSI)

Project Overview

Problem to be solved::   When Digital Cinema standards work began, SMPTE recognized that a reference projector definition was needed to establish the characteristics necessary to properly display D-cinema image content. This document is RP 431-2, D-Cinema Quality — Reference Projector and Environment (2007). This document set the bar for consistent display of D-cinema images in mastering review rooms and in cinemas. It remains relevant today, with the last revision in 2011. Such a document has never been created for D-cinema sound systems. When digital sound on film appeared in the early 1990’s, there was a move to upgrade sound systems in cinemas and mix stages to handle the new digital soundtracks. The majority of the installed sound systems in cinemas today reflect these upgrades, well before the advent of D-cinema. As digital workflows have replaced analog in sound capture, post production, sound design, mixing, and distribution, the impact of movie soundtracks, as created and distributed, has increased dramatically. For example, today’s action soundtracks typically hit and sustain levels of 0 dB FS, which is 20 dB above the SMPTE nominal calibration reference of -20 dB FS = 85 dBC. Mixing stages have substantially upgraded their sound systems over the past decade to accommodate these increased capabilities and the demands of moviemakers. Aside from a relatively small number of premium auditoriums, cinemas have generally not upgraded in a similar fashion. While documents exist that specify cinema sound system electroacoustic response and reference level calibration (SMPTE RP 200, ST 202 and RP 2096-1), no documents exist that detail what is actually required from the B-chain to play back modern movie soundtracks in real time. Several problems result: • A wide variation in the reproduction of soundtracks from cinema to cinema, and especially between the mix stage and the cinema. • Cinema owners have no objective guidelines to reference to know if their current sound system is adequate or needs an upgrade. • Cinema owners and integrators have no objective guidelines when considering buying and outfitting a sound system for a new room. • The filmmakers’ intent and creative impact of the soundtrack is not being well represented to the general public. • When asked to deliver more than their capability, inadequate sound systems can create unpleasant artifacts that irritate listeners and push them away rather than immerse them into the story being told. • Consumers are less inclined to go to the cinema when they don’t feel they will get a true cinematic experience. An inadequate sound system is a contributing factor, which can indirectly result in their decision stay home to watch a movie rather than going to out to the cinema. Engineering documents are needed that specify the necessary parameters and values for cinema sound systems on par with what RP 431-2 specifies for cinema image projection systems. Codifying the expectations of what a cinema sound system must deliver to an audience, consistently and cleanly, will be a great boon for cinema owners and operators. This also has the potential to enhance the moviegoing experience for the consumer and allow them to experience the movie the way it was intended by the filmmaker.
Project scope::   The working group will specify the required parameters and values for a cinema sound system (a.k.a. the cinema B-chain) to faithfully play back modern movie soundtracks in dubbing theaters and cinemas with the sustained high levels and transients that are now common, creating standards documents as needed. The cinema B-Chain includes the cinema processor, routers, amplifiers, loudspeakers, screen and room acoustics. The working group will manage all work necessary. This includes but is not limited to analyzing representative modern soundtracks to identify the pertinent characteristics that challenge cinema sound systems, matching these to measurable parameters of a cinema sound system in situ, and specifying the required values for these parameters to correctly reproduce modern soundtracks. Parameters such as dynamic range, distortion, frequency response, power compression, coverage and room acoustics will be addressed. The emphasis is on the overall B-chain expectations, not of any one component. The anticipated result is a Recommended Practice detailing the required parameters and values to achieve correct reproduction of modern soundtracks. The working group may elect to write other documents as it sees fit, for example, an Engineering Guideline. The working group will liaise with AES, ASA, IOA and other SDO’s, and work closely with them in the creation of these engineering documents.
Specific tasks::   Manage and create subgroups as deemed necessary to: • Analyze representative modern soundtracks to identify the pertinent characteristics that challenge cinema sound systems • Match these to measurable parameters of a cinema sound system in situ • Specify the required values for these parameters to correctly reproduce modern soundtracks. • Create engineering document(s) for consideration by TC-25CSS.
Form of output::   Recommended Practice , Engineering Guideline
Patent Declaration Received? (To be completed prior to FCD):   No


Start: 2019-09-09 | Completed: 2019-10-08