Low Level Extension; Gain Scaling; Processing Hdcd 16-Bit Signals; Hdcd Silence - Pacific Microsonics HDCD Model Two User Manual

Reference
70
®
Model Two HDCD User's Manual
41 and 51 for additional information.

Low Level Extension

Low Level Extension is an average signal level based, low level compression/expansion
system used on HDCD 16-bit amplitude encoded recordings which very gradually raises
gain a preset amount when the average signal level drops below a preset threshold. During
HDCD 16-bit decoded playback the compression curve is expanded back to linear gain by
the HDCD decoder, using a precisely mapped inverse of the curve controlled by a hidden
code, producing a dynamic range and resolution floor beyond 16-bit. Low Level Extension
can be turned On or Off in the Second Operating Menu or the Digital Output HDCD Setup
Menu. The default is Off. See pages 36, 41 and 51 for additional information.

Gain Scaling

HDCD 16-bit recordings using peak extension, when decoded, have an increase of 6 dB in
headroom compared to 16-bit recordings without peak extension. Therefore, it is neces-
sary to scale their playback level up by 6 dB to match the average level of non-peak
extended 16-bit recordings. Gain scaling is accomplished in the digital domain by the
Model Two, which reduces the monitor level by 6dB whenever a 16-bit signal without peak
extension is detected. Gain Scaling can be set to On (automatic) or Off in the Monitor
Setup Menu or the Second Operating Menu. When monitoring 24-bit or 20-bit signals, Gain
Scaling is normally Off. When monitoring 16-bit signals, scaling is normally On (auto-
matic) and monitor gain is increased by 6 dB for HDCD signals with Peak Extend. See pages
42, 57 and 61 for additional information.

Processing HDCD 16-bit Signals

When digital processing of an HDCD encoded 16-bit signal is needed, the Model Two is
first used to convert it to a 24-bit or 20-bit word length. When editing or processing is
completed, the Model Two is used again to convert the signal back to HDCD 16-bit.
Any process or signal path through which HDCD 16-bit amplitude encoded signals are
passed must not affect the bit structure of the signal. Digital processing which alters the
data will destroy the HDCD encoded information located within the LSB of the signal.
Digital processing includes any level changes, EQ, dither, etc. Butt splices or rapid cross
fades are allowable, but certain rules apply. For additional information see page 33.

HDCD Silence

HDCD Silence is automatically generated by the Model Two HDCD Processor when it pro-
duces HDCD encoded output with no input program audio. HDCD silence contains dither
and HDCD code within the LSB of the signal which tells an HDCD decoder that it is an HDCD
signal. For additional information see page 33.
P A C I F I C M I C R O S O N I C S I N C .
Rev. C - January 2002
®