Overview
ISO 8622:1998 specifies the electrical A‑chain frequency response characteristics for playback of magnetic sound records on 70 mm motion‑picture release prints with magnetic stripes. It defines the required reproduction behaviour of the part of the theatrical sound chain that runs from the transducer(s) to the input terminals of the main fader. ISO 8622 is intended for motion‑picture control rooms, indoor theatres, dubbing theatres and review rooms and is used together with related standards to standardize monitor and reproduction characteristics for theatrical sound.
Key topics and technical requirements
- Scope: A‑chain reproduction characteristics for 70 mm magnetic striped prints (type II and type III sound tracks).
- A‑chain definition: The electrical path from playback head/transducer to main fader input (may include de‑emphasis and noise‑reduction decoding where required).
- Frequency‑response tolerances: Measured limits for A‑chain response are specified for playback over different B‑chain alignments (curve N and curve X). Tolerances and graphical curves are provided in table 1 and figures 2–4 of the standard.
- Measurement method: Use a high‑impedance voltmeter accurate from 20 Hz to 20 kHz (±1 dB). Measurements are taken at the fader input terminals (or equivalent) while playing a multi‑frequency test film conforming to ISO 8395.
- Channel balance: In multi‑channel stereophonic installations, electrical output difference between channels at 1 kHz shall not exceed 1 dB.
- Annex A: Normative annex provides reference overall A + B electro‑acoustic response figures; B‑chain contribution requires measurement techniques from ISO 2969.
- Notes: Standard recognizes customary inclusion of de‑emphasis for type II playback and provides guidance on low‑frequency time‑constants and headroom considerations.
Practical applications and users
ISO 8622 is valuable for:
- Cinema and theatre sound engineers aligning playback chains for 70 mm magnetic prints.
- Dubbing mixers and review room technicians standardizing monitor reproduction.
- Manufacturers of reproducers, preamplifiers and playback heads who must meet specified A‑chain electrical characteristics.
- Technical staff responsible for theatrical QA, calibration and archival playback of 70 mm films.
- Standards and compliance teams ensuring compatibility across control rooms and auditoria.
Practical uses include setting acceptance criteria, performing routine calibration checks, defining equipment specifications, and verifying multi‑channel balance for high‑quality theatrical reproduction.
Related standards
- ISO 2969: B‑chain electro‑acoustic response of motion‑picture control rooms and indoor theatres (used for B‑chain alignment curves N and X).
- ISO 8590: Recorded characteristics for 35 mm and 70 mm magnetic striped prints.
- ISO 8395: Multi‑frequency test films for reproduction of 70 mm release prints (test signal source for measurements).
Keywords: ISO 8622, 70 mm, magnetic sound, A‑chain, frequency response, theatrical sound reproduction, control rooms, dubbing theatres.
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