CEA Broadcast Audio and Streaming Standards 1 — Questions and Answers
Question 1: What loudness standard does the ATSC A/85 specification mandate for US broadcast television?
- -23 LUFS
- -16 LUFS
- -24 LKFS (Correct answer)
- -14 LUFS
Correct answer: -24 LKFS
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?
- MP3 (MPEG-1 Audio Layer III)
- Dolby AC-3 (Dolby Digital) (Correct answer)
- AAC (Advanced Audio Coding)
- Opus
Correct answer: Dolby AC-3 (Dolby Digital)
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?
- 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 (Correct answer)
- It applies automatic gain control to dialogue channels independent of music and effects levels
- It sets the minimum loudness floor below which the decoder will not reduce program level
- It adjusts the center channel delay to align dialogue with lip movements on screen
Correct 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
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?
- A narrated commentary track added to a broadcast describing visual elements of a program for blind and visually impaired viewers (Correct answer)
- An embedded metadata track that describes the audio codec and channel configuration of a broadcast stream
- A closed-caption format specifically designed for audio-only radio broadcasts
- A stereo downmix algorithm used when 5.1 broadcasts are played on 2-channel TVs
Correct answer: A narrated commentary track added to a broadcast describing visual elements of a program for blind and visually impaired viewers
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?
- 44.1 kHz / 16-bit
- 48 kHz / 24-bit (Correct answer)
- 96 kHz / 32-bit float
- 32 kHz / 20-bit
Correct answer: 48 kHz / 24-bit
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.
Question 6: What does 'SDI embedded audio' allow in a broadcast facility?
- Distribution of audio as a separate AES3 digital signal alongside the video feed
- Up to 16 channels of uncompressed PCM audio carried within the same Serial Digital Interface (SDI) coaxial cable as the video signal (Correct answer)
- Wireless transmission of broadcast audio using SDI modulation over RF
- Storage of audio metadata in the VANC (Vertical Ancillary) lines of the SDI signal only
Correct answer: Up to 16 channels of uncompressed PCM audio carried within the same Serial Digital Interface (SDI) coaxial cable as the video signal
SDI embedded audio carries up to 16 channels (4 groups × 4 channels) of uncompressed 24-bit PCM audio within the ancillary data space of an SDI video signal. This eliminates the need for separate audio cables, simplifying infrastructure in broadcast facilities and production trucks.
CEA Broadcast Audio and Streaming Standards 1
What loudness standard does the ATSC A/85 specification mandate for US broadcast television?