Grass Valley Imagestore 750 v.3.0.1 - Manual (Page 148)

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Advanced Audio
Dolby
rical 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 conse-
quence 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 con-
sumer mix from a theatrical mix, it is necessary to reduce the surround levels by 3
dB by
enabling this parameter.
• ‘RF Pre-Emphasis’
This parameter is designed to protect against over modulation when a decoded Dolby Digi-
tal bitstream is RF-modulated. When enabled, 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 dis-
abled.
Compression Tab
The following are the compression profile parameters found within the ‘Compression’ tab under
‘Metadata Mode’ in the Imagestore 750 Configurator.
• Profile
This field indicates the RF compression word of the AC-3 bitstream associated with the spec-
ified program.
The setting allows the program provider (or broadcaster) to implement a large dynamic
range reduction (heavy compression) in a way that ensures that a monophonic down-mix
does not exceed a certain peak level. The heavily compressed audio program might be desir-
able for certain listening situations such as movie delivery to a hotel room, or to an airline
seat. The peak level limitation is useful when, for instance, a monophonic down-mix feeds an
RF modulator and over modulation must be avoided.
A compression profile is one of the following:
• None
• Film, Standard
• Film, Light
• Music, Standard
• Music, Light
• Speech
Dynamic Range Tab
Each audio “program” carried within a Dolby E stream has a stream of dynamic range control
profiles associated with it. The dynamic range is composed of the profile to which the value
applies (value between 1 and 8), and the actual dynamic range profile value:
• None
• Film, Standard
• Film, Light
• Music, Standard
• Music, Light
• Speech