"Arny Krueger" wrote in message
...

"Jim Lesurf" wrote in message
...

It is an interesting question. However for myself, the main 'bar' to
giving
any answer is the absence of detailed technical information on HDCD that
would let me determine what *actual* effect the process has... I've read
all sorts of claims and general descriptions over the years that
'describe'
HDCD, but none that would enable any analysis, etc. (Indeed, the
descriptions I've seen at different times contradicted one another!)

I seem to recall that there was an AES conference paper that laid out some
of the details.

My recollection is that HDCD was based on an attenuator that was switched
on and off by proprietary data patterns that were encoded in the LSB. If
your player didn't have the HDCD feature then you got little bursts of
noise at the level of the LSB, which is generally inaudible. If your
player had the HDCD feature, then the trigger data was muted and an
attenuator that extended the dynamic range downward was turned on or off
as needed.

Given that no commercial recordings have more than about 75 dB dynamic
range, the added dynamic range extension beyond the standard CD formats 96
dB or so, is moot.

BTW this manual gives additional information about HDCD processing:

http://www.euphonix.com/support/manu...op_man_301.pdf

Particularly note page 35-37 of the document, the paragraph entitled: "Low
Level Extension"


Peak Extension & HDCD Limiting

"Peak Extension is a restorable (with HDCD decoding) soft peak limiter that
allows peak
levels up to 6 dB above standard full scale level (+6 dBfs) on HDCD 16-bit
recordings
without generating “overs”. The limiter has a carefully crafted “easy-over”
curve, designed
to mimic the sound of analog tape saturation that operates over an input
signal level
range of -3 dBfs to +6 dBfs, in effect squeezing the top 9 dB of the input
signal’s range
into the top 3 dB of the 16-bit recording.

"During HDCD 16-bit decoded playback, Peak Extension peak limiting is undone
by the
HDCD decoder using a precisely mapped inverse of the limiting curve
controlled by the
hidden LSB code, and the dynamics of the original material are restored up
to +6 dBfs, thus
extending dynamic range.

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 compression curve
controlled by
a hidden code, producing a dynamic range and resolution floor beyond 16-bit.
During
undecoded playback low level information normally lost by standard 16-bit
players is preserved,
providing more accurate timbral and spatial reproduction.

"There are two modes of Low Level Extension, “Normal” and “Special”. Normal
mode begins
to affect the input signal 45 dB below peak level, gradually raising the
gain 4 dB as the
level drops over an 18 dB range. Special mode begins to affect the input
signal 39 dB
below peak level, and gradually raises the gain 7.5 dB over a 26 dB range.
Normal mode is
optimized to provide the best combination of decoded dynamic range and
resolution and
undecoded compatibility. Special mode is designed to provide the best
possible decoded
dynamic range and resolution at some potential expense of undecoded
compatibility. To
access Special mode, from the Operating Menu select
(SETUP/OUTPUT/HDCD_16/LOWLVL/
SPECIAL). Typically, Special mode is used only for HDCD 16-bit master
tracking with the
assumption that the recording will be decoded by the Model Two to a 24-bit
or 20-bit word
length for digital post production before being re-encoded to HDCD 16-bit
using Normal
mode to produce a release master.