CEA Broadcast Audio and Streaming Standards

Question 1

What loudness standard does the ATSC A/85 specification mandate for US broadcast television?

Accepted Answer

-24 LKFS

Answer

ATSC A/85 (implemented via the US CALM Act) mandates a target dialogue loudness of -24 LKFS (equivalent to -24 LUFS) with a maximum true peak of -2 dBTP for US broadcast television. This standard prevents loud commercials relative to program content.

Question 2

What audio codec is widely used for digital broadcast audio in the US ATSC standard?

Accepted Answer

Dolby AC-3 (Dolby Digital)

Answer

Dolby AC-3 (Dolby Digital) is the mandatory audio codec for the US ATSC digital television standard. It supports up to 5.1 surround sound at data rates from 32 to 640 kbps and is the primary audio format used in US digital broadcast and DVD.

Question 3

What is the function of 'dialog normalization' (dialnorm) metadata in Dolby AC-3/Dolby Digital broadcast streams?

Accepted Answer

It specifies the average loudness of dialogue in the program, allowing decoders to adjust playback level to a target reference, ensuring consistent perceived loudness between programs

Answer

Dialnorm (dialog normalization) is metadata embedded in AC-3 streams indicating the average dialogue loudness of the program (in dBFS). Decoders use this value to apply a gain offset that normalizes the output to a reference level, preventing loudness jumps between programs or commercials.

Question 4

What is the purpose of 'audio description' (AD) in broadcast audio?

Accepted Answer

A narrated commentary track added to a broadcast describing visual elements of a program for blind and visually impaired viewers

Answer

Audio Description (AD) is a secondary audio service that provides verbal narration describing key visual elements — scene changes, on-screen text, facial expressions, and action — during pauses in dialogue, making television and film content accessible to blind and visually impaired audiences.

Question 5

What sample rate and bit depth are standard for professional broadcast audio in television production?

Accepted Answer

48 kHz / 24-bit

Answer

48 kHz / 24-bit is the industry standard for professional broadcast television audio, as specified by EBU and SMPTE. 48 kHz aligns with the video frame rates used in broadcast (25/29.97/30 fps) and was adopted as the television standard, while 44.1 kHz is used for music CD production.

(CEA) Certified Audio Engineer Practice Test

(CEA) Certified Audio Engineer Practice Test

CEA Broadcast Audio and Streaming Standards