User Manual

Multichannel Monitoring Tutorial Booklet (M2TB) rev. 3.5.2
Masataka Nakahara : SONA Corporation
©2005 YAMAHA Corporation, ©2005 SONA Corporation
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2-5. Down-mixing
Most multi-channel media requires two-channel playback.
There are two possible ways in which content equivalent to a multi-channel production can be mixed to
two channels.
One way is to generate a separate two-channel mix using the individual musical materials (stems) that
were used for multi-channel mixing.
The other way is to use electrical circuitry to forcibly create the two-channel program (fold down).
The fold-down algorithm is defined for each type of media, and the production side must store attenuator
values etc. on the media as meta-data.
Typi cal examples of two-channel fold-down are shown below.
2-5-1. Two-channel fold-down for DVD-Video (Dolby DIGITAL, DTS)
[Fig. 14] Flow of a Down mixing : DVD-Video (Dolby DIGITAL, DTS): Lo/Ro downmix
[Fig. 15] Flow of a Down mixing : DVD-Video (Dolby DIGITAL, DTS): Lt/Rt downmix
In DVD-Video (Dolby Digital, DTS), the above two types of down-mixing (Lo/Ro down-mixing [Fig. 14],
Lt/Rt down-mixing [Fig. 15]) are possible, and the DVD player and AV receiver must have these down-
mixing circuits. One advantage of Lo/Ro down-mixing [Fig. 14] is that the production engineer is able to
select the attenuation values. The playback device performs down-mixing according to the attenuation
values recorded as meta-data on the DVD (however in the case of DTS, Att1=Att2=-3 dB = fixed). On the
other hand, Lt/Rt down-mixing [Fig. 15] allows Dolby Pro Logic, Dolby ProLogic II(x), or DTS NEO:6
decoding to play back surround such as 3-1, 5.1, 6.1, or 7.1 from the two channels Lt/Rt. In the Lt/Rt
down-mix, the surround signals (LS+RS) are mixed in reverse phase with the L channel signal. This
means that if the surround portion and L portion contain a similar signal, the signal may disappear when
down-mixed. To prevent this, 5.1 productions in DVD-Video often apply a 90-degree phase shift to the
LS/RS channels when encoding.
L
Lo
＝
L
＋
Att1
×
C
＋
Att2
×
LS
Ro
＝
R
＋
Att1
×
C
＋
Att2
×
RS
LFE
LS
RS
R
C
Att1
Att2
Att2
-
∞
■
Att1
0.707 (-3dB), 0.596 (-4.5dB), 0.500 (-6dB)
■
Att2
0.707 (-3dB), 0.500 (-6dB), 0.000 (-
∞
dB)
■Default
Att1＝Att2＝0.707 (-3dB)
5.1ch Master
2ch Down-mix
Meta data : Dolby DIGITAL
Att1＝Att2＝0.707 (-3dB)
Fixed : DTS
L
Lt
＝
L
＋
0.707
×
C
−
0.707
×
(LS
＋
RS)
Rt
＝
R
＋
0.707
×
C
＋
0.707
×
(LS
＋
RS)
LFE
(90-degree phase shifted) LS
(90-degree phase shifted) RS
R
C
-3dB
-3dB
-3dB
-
∞
5.1ch Master
2ch Down-mix