Transcript CALM Down?

CALM DOWN!
-24 LKFS
Show
-24 LKFS
Show
-21 LKFS
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-24 LKFS
Show
-21 LKFS
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Downmix Dilemma
Surround Mix
Ls
Lf
L
C
Rf
R
Rs
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Frequent Downmix
Producers
• Stereo Deliverables
Networks
• Stereo Channels & Internet Distribution
Stations
• Stereo Infrastructure & Channels
Consumers
• Stereo STBs & TVs (≥61%)
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Downmix Dilemma
Surround Mix
Ls
?
L
Lf
C
?
Rf
Rs
R
?
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Surround Mix
Preserve Center
L
0 dB
Near Field
C
+6 dB
R
Average
+3 dB
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Preserve Center
Surround Mix
Ls
?
Lf
C
L
∑
R
-3 dB
Rf
Rs
∑
?
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Preserve Rear?
Surround Mix
Ls
Lf
C
Rf
∑
L
Can't Hear
Dialog!
-3 dB
∑
R
Rs
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Adjust Rear
Surround Mix
Ls
-3 dB
Lf
C
L
∑
R
-3 dB
Rf
Rs
∑
-3 dB
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Defacto Standard Downmix
Surround Mix
Ls
-3 dB
Lf
C
L
∑
R
-3 dB
Rf
Rs
∑
-3 dB
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Defacto-Compatible Surround Mix
C
70 dB SPL
∑
C
L
70 dB SPL
-3 dB
∑
R
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Incompatible Surround Mix
Power Sum
10*Log(3) = 4.8 dB
74.8 dB SPL
Lf
C
Rf
Voltage Sum
20*Log (1+.7) = 4.6 dB
Lf
C
Rf
∑
L
Power Sum
10*Log(2) = 3 dB
77.6 dB SPL
∑
R
2.8 dB Error!
-3 dB
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Bottom Line
If two ads are mixed in surround to measure -24 LKFS…
One can sound and measure 2.8 dB louder after downmix
Producers can "game" the system to be louder
Stations and MVPD's could be deemed non-complaint when
broadcasting "compliant" content!
Not a problem when content mixed to be compatible
A real problem for some Public Television music shows
See AES e-Brief 38 for measured statistics
"The Effect of Downmixing on Measured Loudness"
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SOLUTION
Customize the Downmix
Power Sum
10*Log(3)
74.8 dB SPL
Lf
C
Rf
Voltage Sum
20*Log (1+.2) = 1.8 dB
Lf
C
Rf
∑
L
∑
R
-12 dB
Power Sum
10*Log(2) = 3 dB
74.8 dB SPL
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Producer-Controlled Metadata
Producer
Consumer
Ls
Rf
AC3
Audio +
Metadata
AC3
Audio +
Metadata
AC3 Decoder
C
AC3 Encoder
Surround Mix
Lf
Left
Right
Rs
LFE
Manual Metadata
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TV Station-Controlled Metadata
Producers
Networks
TV Stations
Consumers
Ls
AC3
Audio +
Metadata
AC3 Decoder
Rs
AC3 Encoder
Rf
Plant
C
Distribution
Surround Mix
Lf
Left
Right
LFE
X
X
No Metadata Channel!
X
See ATSC A/85 Chapter 7
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Why No Metadata Channel?
Many producers lack interest and ability in setting metadata
For a show, requires adoption by ALL distributors
Within a network, requires adoption by EVERY station
Within a station, requires adoption in ALL equipment
Most equipment requires obscure custom settings
Some equipment cannot carry metadata
Penalty of metadata error is severe: loss of center channel!
*
*
*I'll buy you a beer if you'll let me whine about it.
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Proposed Solution
Standardize downmix for systems without metadata
•
-3 dB for Center and Rear
Require loudness measurement of the standard downmix
•
•
•
Encourages producers to mix appropriate to standard downmix
Producers can use film-style mixing or shift center channel phase
Penalty of an inappropriate mix is merely a show softer in surround
Change delivery standards
Modify A/85
Ask LKFS meter vendors to include downmix measurement
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DISCUSSION