Audio Systems for DTV
ITU Seminar
Kiev, Nov. 14, 2000
Tony Spath
Dolby Laboratories
England
ts@dolby.com
http://www.dolby.com
D
Don’t forget
the audio
D
2
"The cost of entertainment, at least as far
as the hardware is concerned, is falling:
inexpensive chip-sets, lower-cost flatscreen televisions, free or inexpensive
set-top boxes, and not forgetting Dolby
multi-channel surround sound (said by
more than a few experts to have been
responsible for selling more large-screen
televisions that any other technological
advance since colour)."
THE BUSINESS OF DIGITAL TELEVISION by Chris Forrester
Page 7, chapter 1
http://www.bh.com/bookscat/samples/0240516060/0240516060.pdf
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3
UK Household Penetration
Widescreen vs Dolby Surround
17.90%
18.00%
16.00%
14.00%
12.00%
10.00%
8.00%
6.00%
4.00%
2.00%
0.00%
15.20%
Widescreen
Surround
4.90%
1.70%
1998
D
1999
Source: Understanding & Solutions
4
Audio - mono beginnings
TV
D
Mono
Audio
5
Stereo - rather better
L
R
NICAM TV
D
Stereo
Audio
Track
6
Dolby Surround - Matrix audio
L
Stand-alone
or built in to
TVs
R
Stereo
Audio
Track
Pro Logic
Decoder
S
D
C
S
7
5.1 discrete audio
L
C
R
Sub
(the“.1”)
Dolby Digital
Decoder
Digital
Bit Stream
Ls
D
Stand-alone
or built in to
TVs
Rs
8
“5.1” audio is important
n
n
n
D
Surround sound has become very popular
ITU-R Rec. BS.775-1
All new media support 5.1 ch audio
u Movies in the cinema
u Digital Terrestrial TV
u DVD-V and DVD -A
u Digital Cable TV
u Digital Satellite TV
9
The audio systems for DTV:
D
n
MPEG-1,2 Layer II
u DVB
n
Dolby Digital (technical name: “AC-3”)
u ATSC
u DVB
n
MPEG-2 AAC
u ISDB
10
Common attributes of all of these
audio coders
n
n
n
n
D
Significant reduction of bit rate compared to
PCM audio
u compression factors of 6 -1 to 12 -1
Can be used for mono, 2ch stereo, 5.1 ch
Internationally standardized by ISO/IEC or
ITU-R
Open specification and availability of patent
license
11
Differences between coders
n
n
n
n
n
n
D
Efficiency (quality vs bit -rate)
Consumer features to improve audio service
u Level control
u Dynamic range control
u Down-mixing
Cost
Adoption by significant applications
Marketplace success
Technology support
12
MPEG-1 Layer II Technology
n
n
n
D
MPEG-1 Standard
u Mono, 2ch stereo audio
ITU-R Recommendation BS.1115 (2 ch)
Originally developed as coding system for
digital radio
u Eureka 147 (became DAB)
u Basic 2 channel delivery pipe
u Capability to carry aux data
u No consumer features included
13
MPEG-2 Layer II Technology
n
n
n
MPEG-2 Standard – includes 5.1 surround
ITU-R Recommendation BS.1196
MPEG reacted to Dolby announcement of 5.1ch AC-3
u MPEG-2 is MPEG-1 stereo plus a BC (backward
compatible) extension to provide extra channels
MPEG-2 audio frame
(should be >/=640 kbit/s for broadcast quality)
quality
D
MPEG-1
MPEG-1stereo
stereoaudio
audio
Ls,C,Rs
Ls,C,Rsand
andLFE
LFEelements
elements
With
With5.1
5.1transmissions
transmissionsthis
thiswill
willbe
be
aamix
mixof
ofL,C,R,
L,C,R,Ls,Rs.
Ls,Rs. Stereo
Stereo
IRDs
IRDswill
willonly
onlydecode
decodethis
thisportion
portion
These
Theseneed
needtotobe
bere-matrixed
re-matrixedininaa5.1
5.1
decoder
decoderwith
withthe
theMPEG-1
MPEG-1portion
portiontoto
derive
deriveseparate
separateLL&&RRchannels
channels
14
MPEG-2 Layer II Technology
n
n
n
n
D
MPEG-2 Standard
ITU-R Recommendation BS.1196
MPEG reacted to Dolby announcement of 5.1ch AC-3
u MPEG-2 is MPEG-1 stereo plus a BC (backward
compatible) extension to provide extra channels
Technical deficiencies due to BC requirement
u Higher bit rate needed for 5.1 chs
15
MPEG Layer II Adoption
n
n
n
n
n
D
Basic in DVB system (MPEG-1 2ch)
Employed in VCD (MPEG-1 2ch)
Specified for PAL DVD but then rejected
(MPEG-2 5.1ch)
Widely applied for mono, 2ch stereo
u market failure for 5.1 ch
Significant 2ch presence in marketplace
u but not visible to consumers
16
Dolby Digital (AC-3) Technology
n
n
ATSC Standard A/52
Designed specifically to carry any audio
u Mono,
stereo, surround, 5.1
u Consumer features designed in to improve audio
service
n
n
ITU-R Recommendation BS.1196
Designed to balance cost / complexity /
performance
u Key
D
to early and widespread market acceptance
17
Dolby AC-3 Adoption
n
Basic in ATSC system
u Also
n
n
n
n
in U.S. CATV, DBS
Employed in DVD (worldwide)
Used in computer gaming platforms
… for mono, 2ch stereo, 5.1 ch audio
Option in DVB (ETR -154 Annex C)
u Selected
n
by Australia, Singapore, etc.
Substantial and growing presence in home
video marketplace
u Dominant system for 5.1 ch
u Highly visible to consumers
P
D
18
DVD – the PAL format that
nearly wasn’t
n
n
n
D
Compromise standard
u NTSC 525/60 disc use AC -3 (like ATSC)
u PAL 625/50 disc use Layer II (like DVB)
Unsuccessful launch of PAL 625/50 format
u Lack of support for MPEG-2 audio
u Poor performance of MPEG -2 audio
Standard changed so AC-3 could be used in
all discs
u Marketplace decision which to use on PAL
625/50 discs
19
D
20
D
21
Dolby Digital in DVB
Panasonic ad for German broadcaster ProSieben
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22
MPEG-2 AAC Technology
n
n
n
MPEG-2 standard (part 7)
Developed after Dolby, AT&T showed that
non-BC codecs could offer higher
performance than the BC Layer II standard
Main contributions from 4 partners
F AT&T,
Dolby, Frauenhofer , Sony
F Dolby administers the patent licensing
n
D
Higher performance & complexity than other
codecs
23
MPEG-2 AAC Adoption
n
n
n
n
D
Basic in ISDB system
Employed in internet audio, solid state audio
players, some digital radio
Used for mono, 2ch stereo
u not yet applied to 5.1 ch
Growing presence in music delivery
marketplace
u But no presence in home video (yet?)
24
Audio Quality (CRC test)
D
25
Bit rate for high quality 5.1 ch
n
n
n
D
MPEG-2 Layer II
u 640 kb/s
u 448 kb/s (average - with variable bit rate)
u no significant commercial usage
Dolby Digital (AC-3)
u 384 - 448 kb/s
u extensive usage in DVD, LD, DTV
MPEG-2 AAC
u 320 kb/s
u no commercial usage (yet)
26
Important Consumer Features
n
Level control in the decoder
u Achieve uniform loudness / Avoid level changes:
between program segments
F between channels, signal sources
F
n
Dynamic range control
u Capability to deliver both:
wide dynamic range for audio enthusiast
F narrow dynamic range for general listeners
F
n
D
Downmixing
u Serve mono, 2 ch and 5.1 ch listeners with the
same bit stream
27
Typical audio signals
ACTION
MOVIE
DRAMA SPORTS SYMPHONY
ROCK
NEWS
0 dBFS
-10 dBFS
-20 dBFS
-30 dBFS
-40 dBFS
AVERAGE DIALOG
D
SIGNAL PEAKS
28
How we broadcast audio today
ACTION
MOVIE
DRAMA SPORTS SYMPHONY
ROCK
NEWS
0 dBFS
-10 dBFS
-20 dBFS
-30 dBFS
-40 dBFS
AVERAGE / DIALOG
D
SIGNAL PEAKS
29
Typical audio signals
ACTION
MOVIE
DRAMA SPORTS SYMPHONY
ROCK
NEWS
0 dBFS
10
-10 dBFS
-20 dBFS
-30 dBFS
27
24
21
20
20
-40 dBFS
AVERAGE DIALOG
D
SIGNAL PEAKS
30
Normalized audio signals
ACTION
MOVIE
DRAMA SPORTS SYMPHONY
ROCK
NEWS
0 dBFS
-10 dBFS
-20 dBFS
-30 dBFS
-40 dBFS
AVERAGE DIALOG
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SIGNAL PEAKS
31
Dynamic range control
dBFS
Original
Signal
Hi Fi Stereo
Reproduction
Mono TV
Reproduction
0
-10
-20
HIGH LEVEL
DYNAMICS
-30
-40
-50
LOW LEVEL
DYNAMICS
-60
-70
-80
D
32
Downmixing
n
n
n
D
Optimize downmix at decoder
u Mono compatible
u Surround compatible
Match level between 2ch and 5.1 ch content
Avoid clipping / overload of downmix
u 14 dB buildup in level of mono downmix!
33
Downmixing: One Bit-stream
for all
DIGITAL
SET-TOP BOX
HOME THEATER
DVD
TERRESTRIAL
CABLE
SATELLITE
DIGITAL
PASS
THROUGH
5.1
DISCRETE
HOME THEATER
DOLBY
DIGITAL
ENCODER
D
A SINGLE
BITSTREAM
DELIVERED
TO MANY
RECEIVERS
Lt / Rt
DOWNMIX
PRO
LOGIC
HI-FI VCR
STEREO
DOWNMIX
STEREO,
HEADPHONES
MONO
DOWNMIX
TV RF REMOD
34
Implementation Status of
Consumer Features
n
n
n
D
Dolby Digital (AC-3)
u First system designed to include these features
u Universal implementation
MPEG Layer II
u Dolby Digital feature set recently copied and
documented in ETR-154 Annex D
u Negligible implementation
MPEG-2 AAC
u Some specifications to enable in specification
u Negligible implementation
u No coordinating entity to ensure consistency
35
Licensing for MPEG Layer II
n
D
Layer II
u Basic patent only license for CE
manufacturers
u No support with know-how
36
Licensing for AC-3
n
n
D
Patent plus know-how license for CE
manufacturers.
u No royalty on IC’s
u Reference code provided
u Comprehensive design manual
Extensive support of licensees
u Support during design phase
u Test and verification of all product models
u Visit licensees twice per year
37
Licensing for AAC
n
n
Basic patent-only license issued by Dolby
u For patents owned by AT&T, Dolby,
Frauenhofer, Sony
Know-how can be purchased for an extra
charge
u Dolby will offer a know-how package
u Dolby support for AAC will not be as
extensive as Dolby support for AC-3
F Due
D
to relative market sizes
38
License fees - 2ch product
US $
CE Company Sales Volume
1.2
1
0.8
0.6
0.4
0.2
0
Low
Med
High
Layer II (patent)
AC-3 (patent+knowhow)
AAC (patent)
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39
License fees - 5.1ch product
US $
CE Company Sales Volume
2.5
2
1.5
1
0.5
0
Low
Med
High
Layer II (patent)
AC-3 (patent+knowhow)
AAC (patent)
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40
Dolby Digital Marketplace
Dolby Digital Units (Cumulative)
70,000,000
2 channel Radio
2-channel TV
5-channel TV
60,000,000
50,000,000
DVD-Video units
DVD-ROM units
40,000,000
5.1 channel units
30,000,000
20,000,000
10,000,000
0
1/96 2/96 3/96 4/96 1/97 2/97 3/97 4/97 1/98 2/98 3/98 4/98 1/99 2/99 3/99 4/99 1/00
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41
Dolby Digital at home
Set
Set Top
Top Box
Box
DVD
DVDPlayer
Player
DTV
DTVSet
Set
Gaming
Gaming
Platform
Platform
Common
Common
Interconnect:
Interconnect:
Dolby
DolbyDigital
Digital
Decoder
Decoder
++66channel
channelamp
amp
D
IEC61937
IEC61937
42
Growth in 5.1 ch Dolby Digital
A/V Receivers - Cumulative
Millions
20
15
AC-3
Layer II
AAC
10
5
0
1996 1997 1998 1999 2000
(est)
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43
DVD players with Dolby Digital
D
44
Full 5.1 ch Dolby Digital receiver
D
45
Dolby Digital in a box
D
46
Major considerations for selection
of audio coding for DTV
n
5.1 channel audio is very important
- the future of audio is surround
u AAC and AC-3 score better than MPEG LII
F Based
on technical attributes and market
success
n
D
Compatibility with other 5.1 ch media (DVD)
u AC-3 scores best
u MPEG Layer II has failed in 5.1
u AAC - ???? (perhaps)
47
Is AAC a viable 5.1 ch solution ?
n
n
n
D
Only current likely application for 5.1 ch AAC is ISDB
in Japan
The market for 5.1 ch AAC products must be
substantial before AAC is well supported
u Limited application areas of 5.1 ch AAC
u Subset of any market uses 5.1 ch vs 2ch
u Unclear if 5.1ch AAC will reach ‘critical mass’
Dolby will provide some support for AAC 5.1 ch
u but much less than the support we give AC-3 (due
to relative market sizes and generated revenue)
48
Logical Conclusions
n
n
D
AAC is the best “technical solution”
u Coding efficiency
AC-3 offers best balance of all factors
u Cost
u Complexity
u Support
u Interoperability
u Consumer recognition and acceptance
49
Audio in DTV Systems
n
n
n
ATSC
u Dolby Digital (AC-3) is sole audio solution
DVB
u Layer II 2ch stereo mandated
u Option to include AC-3
ISDB
u AAC mandated
F Could
be modified to include AC-3 as
alternative
D
50
Conclusions and Recommendations
n
n
A DTV system should be able to offer 5.1 ch
audio (even if transmissions start with stereo
or mono)
From a 5.1 ch audio viewpoint:
u ATSC with AC-3 is a solid choice
u DVB with the AC-3 option is a solid choice
F Important
to mandate this option in all receivers
to avoid wasting bits on MPEG-1 simulcast
u ISDB
with AAC is a unknown
F Risk
D
could be eliminated by specifying ISDB
with AC-3
51
Don’t forget
the audio
D
52
Audio Systems for DTV
Thank You
Tony Spath
Dolby Laboratories
England
ts@dolby.com
http://www.dolby.com
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