Dynamic Range Management in Proposed ATSC Recommended Practice A/85 Kenneth Hunold Broadcast Applications Engineer Dolby Laboratories, Inc.
Dynamic Range Control (DRC) in DTV Audio (AC-3) Where did the idea come from? What does it do? How is it implemented? What are the results? 2
1991: ATSC Specialist Group on Digital Services There is a conflict between the needs of many viewers for program audio to have a narrow dynamic range, and the desires of some viewers to reproduce the audio in the full dynamic range intended by the audio producer. The ATV audio coding system should incorporate an integrated dynamic range compression method which delivers data to the receiver representing the compression characteristics employed. The preferred compression method will bring loud sounds down towards the dialogue level, and quiet sounds up towards the dialogue level. 3
Dynamic Range Management in DTV Audio Unlike traditional analog broadcasting, DRC is implemented in digital television as a separate process, preceded by proper Loudness Management Two approaches to Dynamic Range Control: Dynamic Range Control using audio metadata (reversible) Traditional audio dynamics processing (irreversible) Hybrid approach: Combination of both methods 4
DRC via Metadata Designed to provide program producers with the greatest freedom to determine the dynamics of their content Producers can monitor (emulate) how the program will sound with reduced dynamic range during production Broadcasters can pass the producer s choices on to the viewers as metadata Viewer s receiving equipment will choose to reduce the dynamic range by default Viewers may choose to ignore the DRC metadata in order to listen to programs with the original dynamics 5
DRC via Metadata DRC calculations are made in the AC-3 encoder Calculated gain words are placed into the coded audio stream as metadata These gain words and the original, unmodified audio are sent to every decoder The gain words are applied in the AC-3 decoder inside the consumer s receiver Encoder-calculated gain words are applied to the decoded audio as a momentary gain change (Or not, if the viewer wants to hear the original dynamics) There are no compressor/limiters in AC-3 decoders 6
Dynamic Range Control Overview 7
DRC Profiles 8
DRC Profiles Music Light Music Standard Film Light Film Standard Speech 9
DRC Profiles 10
Line and RF Mode Two types of DRC are calculated in the encoder One type for slightly reducing the program s dynamic range Suitable for baseband, line level interconnection of consumer devices Called Line Mode DRC, or dynrng Another type for more aggressive DRC control Suitable for connection to TV sets, cable STBs, or other devices that have RF connections Called RF Mode DRC, or compr 11
Line and RF Mode TV receivers and cable set-top boxes will use RF Mode DRC by default A/V receivers will use Line Mode DRC by default CE devices may provide a menu choice to select either DRC mode, or to ignore the DRC signal (and hear the original program dynamics) Late Night or Midnight modes use the RF Mode DRC gain words TV or STB guide menu choices may not be consistent among manufacturers 12
The None Profile Choosing None does not select any of the DRC profiles DRC Gain words are not calculated In order for the AC-3 DRC system to be functional, a profile other than None should be selected 13
Using the None Profile Ramifications: DRC control will not be available to the consumer Late Night or Midnight modes will not be available Dynamic Range must be managed by some other means Wide dynamic range programs may cause distortion in sets with limited volume capability Protection Limiting may be generated by the encoder to prevent clipping in the decoder HD signal conversion to SD for analog cable tiers will not be able to use DRC to match other analog signals 14
DRC Metadata Review and Example 15
Program Segment Loudness -20-15 -10 LKFS) 16-40 -35-30 -25 00:01 00:07 00:13 00:19 00:25 00:31 00:37 00:43 00:49 00:55 01:01 01:07 01:13 01:19 01:25 01:31 01:37 01:43 01:49 01:55 02:01 02:07 02:13 02:19 02:25 02:31 02:37 02:43 02:49 02:55 03:01 03:07 03:13 Time Loudness (L All Dialogue
Program Segment Loudness and Dialnorm Value -10-15 -20-25 17 Loudness (LKFS) -30-35 -40 00:01 00:07 00:13 00:19 00:25 00:31 00:37 00:43 00:49 00:55 01:01 01:07 01:13 01:19 01:25 01:31 01:37 01:43 01:49 01:55 02:01 02:07 02:13 02:19 02:25 02:31 02:37 02:43 02:49 02:55 03:01 03:07 03:13 Time All Dialogue Dialnorm
The Comfort Zone 10.8 Annoyingly Loud 5.6 Turn Volume Down Comfort Zone 2.4-5.4 0 Louder, but Acceptable Softer, but Acceptable -10.2 Turn Volume Up -19.1 Annoyingly Soft Relative Loudness (in db) of the Listening levels investigated, with 95% confidence intervals 18
Program Segment Loudness and Comfort Zone -10-15 -20-25 19 Loudness (LKFS) -30-35 -40 00:01 00:07 00:13 00:19 00:25 00:31 00:37 00:43 00:49 00:55 01:01 01:07 01:13 01:19 01:25 01:31 01:37 01:43 01:49 01:55 02:01 02:07 02:13 02:19 02:25 02:31 02:37 02:43 02:49 02:55 03:01 03:07 03:13 Time All Dialogue Dialnorm
Program Segment Loudness with Dynamic Range Control (DRC) -10-15 -20-25 20 Loudness (LKFS) -30-35 -40 00:01 00:07 00:13 00:19 00:25 00:31 00:37 00:43 00:49 00:55 01:01 01:07 01:13 01:19 01:25 01:31 01:37 01:43 01:49 01:55 02:01 02:07 02:13 02:19 02:25 02:31 02:37 02:43 02:49 02:55 03:01 03:07 03:13 Time Original Dialnorm All w/drc Dialogue w/drc
The Comfort Zone 10.8 Annoyingly Loud 5.6 Turn Volume Down Comfort Zone 2.4-5.4 0 Louder, but Acceptable Softer, but Acceptable -10.2 Turn Volume Up -19.1 Annoyingly Soft Relative Loudness (in db) of the Listening levels investigated, with 95% confidence intervals 21
Program Segment Loudness with DRC and Turn up/ Turn down Zone -10-15 -20-25 22 Loudness (LKFS) -30-35 -40 00:01 00:07 00:13 00:19 00:25 00:31 00:37 00:43 00:49 00:55 01:01 01:07 01:13 01:19 01:25 01:31 01:37 01:43 01:49 01:55 02:01 02:07 02:13 02:19 02:25 02:31 02:37 02:43 02:49 02:55 03:01 03:07 03:13 Time Original Dialnorm All w/drc Dialogue w/drc
Re-cap: Audio metadata provides a powerful way to separately manage program loudness and dynamic range AC-3 DRC is not intended to re-master a program or as a substitute for artistic DRC management by the program producer Loudness management separately implemented with dialnorm Dynamic Range control is enabled by default, but can be undone by viewers to hear original program dynamics, if desired. These tools exist in every AC-3 encoder and decoder 23