Volume in Production and Post-Production Phases: Measurement Procedures

The measurement of volume levels in production and post-production phases is regulated by Circular 34 as follows:

- Volume meters using the "EBU mode" measurement mechanism support three measuring time frames, with M and S time windows used for real-time level measurement and audio signal mixing processing. The initialization level setting process can be best performed with the M volume meter for adjusting the levels of the main components, the "anchor" components of the audio signal (dialogue, music, or sound effects) to approach the target level of -23 LUFS. The mixer itself can know the volume at any actual moment of the signal as per M and S measurement policies.

- Due to inconsistencies between ITU-R BS. 1770 and ITU-R BS. 1771, this standard suggests the following notations:

- The notation for Loudness Level, K-weighted is "Lk."- The unit "LUFS" indicates the value of Lk on the digital full scale.- The notation "LU" indicates the value of Lk describing the relative reference result or the difference in loudness levels compared to the reference level.

Simultaneously, Circular 34 also dictates that the interface of any volume meter compatible with the "EBU mode" will define 2 scales: the "EBU +9 Scale" commonly used for most programs, and the "EBU +18 Scale" only used for programs with wide LRA. Both scales may display the relative loudness value in LU, or the absolute value in LUFS. Specifically, "0 LU" in the "EBU mode" corresponds to the target level of -23 LUFS.

See details in Circular 34/2017/TT-BTTTT effective from July 1, 2018.

-Thao Uyen-

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