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CHAPTER 1
DRAWMER DC2476 DIGITAL
MASTERING PROCESSOR
INTRODUCTION
The Drawmer DC2476 is an extremely sophisticated, all-digital stereo
mastering processor designed for use in demanding recording and
broadcast applications. Both analogue (balanced XLR) and digital (AES/
EBU and S/PDIF) I/O is provided as standard. The audio converters are
24-bit and the digital output can be either 16, 18, 20 or 24-bit at sample
rates of up to 96kHz. Noise shaped dithering is included and Word Clock
input and output is available. A new feature is Output Trim which sets the
maximumlevelthat output can reach, even in bypass, making the DC2476
easierto use in a broadcast environment.
Designed to be extremely easy and intuitive to use, the Drawmer DC2476
comprises a stage of dynamic equalisation, also incorporating full-band
compression(the DQ stage), followed by a five-band equaliser modelled on
the response of classic analogue filters. The signal is then split into three
user definable bands where it is routed via a three-band expander, a three-
band compressor, a three-band limiter and a three-band modelled tube
saturation stage. The three bands are then recombined before being fed to
the output stage via a fader system that can be used to generate precise
fade-insand fade-outs of user definablelength.The output stage itself offers
a number of dither options.
Although a wide range of manual control is provided, an automated gain
management system is used in addition to 'Programme Adaptive' time
constant management in the compressor and expander stages. The
automatic gain management monitors the signal level at critical points
throughout the signal chain and automatically reduces levels in situations
when overloads would otherwise occur. This makes the Drawmer DC2476
impossible to overload. Another key feature is the use of a 'Bootstrap'
compressor.Conventionalcompressorsreduce thelevelof audiopeaks,which
means make-up gain has to be applied to restore the same peak level. The
DrawmerDC2476 worksthe other wayaround by insteadincreasing thelevel
ofquieter signals and leaving the peak levelsattheir original values.
Thismakes setting up far more intuitive when adjusting the individual bands
of a multi-band compressor and also avoids the necessity to juggle the
make-up gain control settings.
Why 96kHz?
Digitalprocessing has untilnow been confined to48kHz sampling frequency.
In order to achieve the required bandwidth for professional audio, a very
severe low pass filter at 23kHz is required to separate analogue signal
frequenciesfrom theclock frequencyotherwise unpleasantaliasingwill occur.
This requires the use of a FIR digital filter which is part of the A/D and D/A
converters. Unfortunately thesefilters cause whatis known as >timesmear=,
where short transients are smeared over a longer time period giving loss of
HF detail. At 96kHz sample frequency, the low pass filter is less severe and
at twice the frequency, so time smear is considerably reduced.
A second important consideration is the increased audio bandwidth up to
40kHz. This allows harmonics which extend above human hearing to be
generated and preserved. These harmonics, although not audible
themselves, make a contribution to the sound quality.
Finally, the user interface has been designed tomakethe Drawmer DC2476
as simple to operate as possible. In fact, once you’ve got used to using the
cursor buttons, the Adjust knob and the Adjust knob push switch to move
aroundthe various screensand their parameters,operationis almost entirely
intuitive. Custom graphics are used wherever possible to monitor the
processorfunctionandits adjustmentswhile frontpanel LEDbargraph meters
constantlymonitor the input and output signal levels, limiter activity,plusthe
amountof gain reductionbeingapplied in eachofthe three frequency bands.
