CALREC Putting Sound in the Picture 127
LO/RO & LT/RT DOWNMIX ENCODING
The patchable downmix output of each
surround Main output bus can be set to be
either an Lo/Ro or an Lt/Rt format.
Lo is a mix of Left front, Left rear, Centre
and Lfe content. Ro is a mix of Right
front, Right rear, Centre and Lfe content.
By default, Lfe does not contribute to
the downmix, but it can be added. The
contribution of each part is determined by
the default downmix setting applied and can
be adjusted using spill faders in downmix
mode.
Lt/Rt is often referred to as an encoded
output. The surround legs are summed
together in a similar way to Lo/Ro,
however phase changes are made to some
of the content before summing which
allow surround decoders to ‘unfold’ the
stereo signal back to discrete surround
that matches the original 5.1 output of the
console.
Lo/Ro, like any stereo signal can be
‘decoded’ to produce a 5.1 path, however
without the phase encoding of Lt/Rt the
result will not match that of the original 5.1.
Note, when a main output is set for Lt/Rt,
only the downmix audio patched to output
ports is phase encoded. Any internal
routing of the surround main output to
stereo destinations remains as LoRo. For
example, if a surround Main 1 bus is routed
on to stereo only Main 2 bus, or if a full
surround bus is being monitored in stereo
i.e the chosen source is full 5.1 but the
monitor is in stereo mode. Fig 1 shows the
Main Output patching for Main 1 its Lt Rt
appear at the bottom of the Main 1 Leg
Type column.
Lt/Rt outputs conform to the downmix
settings applied on the main application
>Operate>Spill D-MIX page, however
they are NOT affected if the downmix
settings are adjusted from a spill panel in
downmix mode. When in Lt/Rt mode,
changes made to the downmix from the
Spill panel in downmix mode are still
affecting the LoRo and can therefore
affect Main to Main routing or stereo only
monitoring as described above.
Note that because the number of
main outputs is halved at higher
sample rates, the number of available
LtRt downmixes is also halved so
only 8 Lt Rt processes will be made
available at 96kHz.
FIG 2 - MAIN APPLICATION, OPERATE>BUS CONFIG>MNS/GPS
FIG 1 - MAIN OUTPUT PATCHING
Selecting Lt/Rt or Lo/Ro
The downmix format for surround main
output patching is selected from the
>Operate>Bus Config>Mns/Gps page
of the main application., see Fig 2 below.
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