Grass Valley Imagestore 750 v.2.0.1 - Manual (Page 373)

Imagestore 750 User Manual Dolby Decode/Encode
Miranda Technologies Inc. Page 373
minimal impact when the Dolby Digital program is decoded to 5.1 channels,
but provides a Lt/Rt output that can be Pro Logic® decoded to L, C, R, and
S, if desired. However, for some phase-critical material (such as music) this
phase shift is audible when listening in 5.1 channels. Likewise some material
down-mixes to a satisfactory Lt/Rt signal without needing this phase shift. It
is therefore important to balance the needs of the 5.1 mix and the Lt/Rt
downmix for each program. This parameter is not sent to the consumer
decoder.
Surround Attenuation
The Surround 3 dB Attenuation frame element determines whether the
surround channel(s) are attenuated 3 dB before encoding. It is used to
compensate for the level of the surround signal(s) originating from a
theatrical mixing room (dubbing stage) and those originating from mixing
rooms used for Television and DVDs. For compatibility with older film
formats, theatrical mixing rooms set the surround playback channel
sensitivity (and thus the reproduced SPL) 3 dB lower than the sensitivity
(thus reproduced SPL) of the front channels. The consequence is that the
surround signal levels on tapes produced in a dubbing stage are 3 dB higher
than those produced in a consumer mixing room. Therefore, to convert to a
consumer mix from a theatrical mix, it is necessary to reduce the surround
levels by 3 dB by enabling this frame element.
RF Pre-emphasis
This frame element is designed to protect against over modulation when a
decoded Dolby Digital bitstream is RF modulated. When enabled ("1") the
Dolby Digital encoder includes pre-emphasis in its calculations for RF Mode
compression. The parameter has no effect when decoding using Line Mode
compression. Except in rare cases, this parameter should be disabled.
Compression Tab
The following section describes the compression profile parameter found
within the “Compression” tab in Metadata Mode.