Overview
ISO 22234:2005 defines measurement methods and target wide‑band sound pressure levels for multi‑channel motion‑picture sound reproduction in control rooms, review rooms and indoor theatres. It covers playback systems used for analog photographic film audio, digital photographic film audio and D‑cinema audio, and is intended to standardize how motion‑picture sound is reproduced and verified together with ISO 2969.
Key topics and technical requirements
- Reference level: The standard specifies an absolute reference sound pressure level of 85 dB (C‑weighted) for normal theatrical operation.
- Test signal: Use wide‑band pink noise inserted prior to the main fader (or equivalent insertion point) at the reference recorded level (≈50% modulation on analog film or typically 20 dB below 100% on digital).
- Electroacoustic response: Confirm each channel complies with ISO 2969 before SPL measurements.
- Measurement equipment:
- Screen and surround channels: wide‑band sound level meter, C‑weighting, slow response.
- Sub‑woofer/LFE: one‑third‑octave real‑time analyser (RTA) or SLM with one‑third‑octave filters (wide‑band SLMs are not reliable for sub‑low frequencies).
- Measurement procedure:
- Measure each channel with pink noise one channel at a time; spatially average measurements within the normal seating area (single location may be position S).
- Sub‑woofer: measure at a minimum of four positions and average over ≥30 s.
- Surround channel alignment:
- Single surround: level equals absolute sound pressure level.
- Two surrounds: each channel normally set ≈3 dB below absolute so their in‑phase sum equals the absolute level (may vary with array geometry).
- Three or more surrounds: set individual channels equivalent to a single channel of a two‑channel system.
- Sub‑woofer/LFE behavior:
- Discrete LFE (digital/D‑cinema): show ~10 dB in‑band gain vs a wide‑band screen channel on RTA.
- Analog bass‑extension systems: no in‑band gain; combined centre + sub shows ~3 dB gain in overlapping band.
Practical applications and users
ISO 22234 is used for:
- Commissioning and calibration of cinema and dubbing theatres
- Quality control when aligning playback chains (B‑chain)
- Compatibility checks between analog, digital and D‑cinema playback
- Troubleshooting low‑frequency or channel‑balance issues
Typical users:
- Theatre and cinema audio technicians
- Dubbing/review room engineers and re-recording mixers
- Acousticians and systems integrators
- Cinema exhibitors, equipment manufacturers and QA teams
Related standards
- ISO 2969 - B‑chain electro‑acoustic response (required companion)
- IEC 60268‑17 - Standard volume indicators
- IEC 61672‑1 - Sound level meters
- SMPTE RP 200 / SMPTE 202 (bibliography) - related cinema practice guidance
Keywords: ISO 22234:2005, motion‑picture sound, sound pressure levels, B‑chain, D‑cinema, pink noise, sub‑woofer, LFE, electroacoustic response, cinema calibration.