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CPP100
SECTION 1
CPP1OPS
25/10/06
www.snellwilcox.com
Version 1 Issue 6
1.1
Description
Compressors demand extremely high quality inputs if
artefacts are to be minimised. A compressor may
work well on clean signals from a component digital
recorder, but real world signals from analogue,
composite or film sources can cause serious
problems.
MPEG works by sending the differences between
successive pictures. Noise is particularly difficult as it
causes random changes from one picture to the next.
The compressor tries to encode these changes,
using up valuable data capacity. With the powerful
noise reduction and pre-processing of PREFIX a
compressor can more fully utilise the available
bandwidth.
PREFIX operates in the component 4:2:2 domain and
has a number of distinct filters; each ‘tuned’ to
remove a specific type of noise.
As well as reducing noise, for picture sources that
have been band limited PREFIX contains a
sophisticated detail enhancer. The enhancer works to
‘sharpen’ detail in the picture without introducing
ringing or overshoots normally associated with
enhancers. The level of enhancement can be
subjectively selected by the user to suit the bandwidth
of the material and coring facilities ensure that low
level noise is not enhanced.
Residual subcarrier and cross effects can also cause
a compressor similar problems; hence PREFIX
contains an adaptive field based digital comb filter
capable
of
providing
excellent
luma/chroma
separation. The design utilises techniques derived
from work pioneered by the BBC Research
department, and ensures exceptional stability,
excellent subcarrier rejection and repeatable results.
PREFIX also has a number of other features
including test pattern generation, SMPTE-259M-C
digital component inputs, an integral synchroniser,
capable of genlocking to either an analogue studio
reference or the currently selected input, and unique
picture splitting facilities.
The ‘Golden Gate’ decoder option is the latest Snell &
Wilcox decoder and was developed with both digital
and analogue composite input.
The system’s functionality can be controlled from the
active front panel. Alternatively the units can be
controlled remotely from a RollCall “shoebox” remote
control unit or PC.
The processor cards are housed in a 1RU, 19-inch
rack that also contains the automatic switched mode
power supply, axial cooling fan and connectors.