HDCD re-encoding
 

Been having a play around with some HDCD discs (my Arcam DV-79 will
decode HDCD). With the HDCD filter in place they do sound considerably
better than without (but it has to be said, no better than a normal CD
that hasn't been compressed to buggery).

Comparisons done with analogue out from DVD player (which has HDCD
decoding) against DAC on amplifier (Arcam AVR-250). With non-HDCD discs
it's all but impossible to tell what's in use when using straight stereo
mode (the DAC in the amp sounds slightly better when using any of the
DSP modes, which would make sense - signal stays digital until the last
possible moment).

So short of doing an analogue "rip", is it possible to decode HDCD in
software and dither it down to 16-bit linear before encoding it as an
MP3, to avoid compression on playback?

--
Glenn Richards Tel: (01453) 845735
Squirrel Solutions http://www.squirrelsolutions.co.uk/

IT consultancy, hardware and software support, broadband installation

HDCD re-encoding
 

Glenn Richards wrote:

So short of doing an analogue "rip", is it possible to decode HDCD in
software and dither it down to 16-bit linear before encoding it as an
MP3, to avoid compression on playback?

Part of the licence agreement is, if I recall correctly, that the decoded
signal is not available digitally.
If you have a suitable sound card (24 bit) then Windows Media Player will decode
HDCD.
So it might be possible to use Total Recorder or some such program that
will insert itself between computer and soundcard to copy the music at 24/44.1.
I haven't tried it yet.

--
Eiron

No good deed ever goes unpunished.

HDCD re-encoding
 

Eiron wrote:

Part of the licence agreement is, if I recall correctly, that the decoded
signal is not available digitally.

Hmmm...

So what about, say, if I were to connect a standalone CD recorder to the
analogue outputs of the DV-79 and make an analogue copy of the disc to a
CD-RW, then rip the analogue copy?

Obviously that would work from a functional level, but how do you think
it would sound? Logic suggests it would actually sound ok as most CD
recorders are pretty transparent... opinions?

--
Glenn Richards Tel: (01453) 845735
Squirrel Solutions http://www.squirrelsolutions.co.uk/

IT consultancy, hardware and software support, broadband installation

HDCD re-encoding
 

In article , Eiron
wrote:
Glenn Richards wrote:

So short of doing an analogue "rip", is it possible to decode HDCD in
software and dither it down to 16-bit linear before encoding it as an
MP3, to avoid compression on playback?

Part of the licence agreement is, if I recall correctly, that the
decoded signal is not available digitally.

Erm... That may hinge on what they define as the 'decoded signal'.

My understanding of HDCD is that is repatterns the least significant bits
of the series of 16bit digital values in a proprietary way that the HDCD
decoder exploits in some way.

That would not prevent, say, an SPDIF output from giving you the (encoded)
series of 16bit values as they are present on the CD. Ditto for reading the
CD with something like a computer. Neither of these processes would
'decode' the HDCD data, just copy it with the bits in their 'encoded'
pattern.

I can't recall seeing a full and detailed technical description of the HDCD
system, so for all I know, though, the non-audio data on the disc may
contain some 'extra' info that tells the HDCD decoder 'this is an HDCD
disc' in such a way that a simple 'clone' of the audio data would not
duplicate. So far as I know, I have no HDCD discs, and none of my CD
players contain a decoder.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

HDCD re-encoding
 

In article , Glenn Richards
wrote:
Eiron wrote:

Part of the licence agreement is, if I recall correctly, that the
decoded signal is not available digitally.

Hmmm...

So what about, say, if I were to connect a standalone CD recorder to the
analogue outputs of the DV-79 and make an analogue copy of the disc to
a CD-RW, then rip the analogue copy?

Obviously that would work from a functional level, but how do you think
it would sound? Logic suggests it would actually sound ok as most CD
recorders are pretty transparent... opinions?

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!)

My understanding has been that the process is 'proprietary' so the relevant
details are not in the public domain. If this is incorrect, I'd welcome a
pointer to where the info is available. :-)

A secondary point is that - since the HDCD data is still at the same
information channel capacity as 'normal' CD audio - the results might
depend on how HDCD compares with any noise-shaping, etc, the converters
employed actually use.

More generally, though, I find that provided I avoid problems like
clipping, that the sound when I replay a CD I have recorded from an
analogue source sounds to me just like the source I recorded. Hence I'd be
inclined to expect this of the analog from an HDCD player as well... But
this is simply an expectation, not an actual result. :-)

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

HDCD re-encoding
 

"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.

HDCD re-encoding
 

Jim Lesurf wrote:
That would not prevent, say, an SPDIF output from giving you the (encoded)
series of 16bit values as they are present on the CD. Ditto for reading the
CD with something like a computer. Neither of these processes would
'decode' the HDCD data, just copy it with the bits in their 'encoded'
pattern.

I can't recall seeing a full and detailed technical description of the HDCD
system, so for all I know, though, the non-audio data on the disc may
contain some 'extra' info that tells the HDCD decoder 'this is an HDCD
disc' in such a way that a simple 'clone' of the audio data would not
duplicate.

Copying CDs on a computer does work, the HDCD is intact.

I did a test, recorded rear panel SPDIF from my HDCD Rotel RCD-971
playing a HDCD disc, to a computer (SPDIF interfaced, true 44.1KHz no
soundcard internal digital bus resampling). The Wav file has LSB info
(did hex dump), but on burning it to a CD and replaying it - the HDCD
decoder doesn't kick in. It could be my SPDIF to Wav process is up the
spout though (cheap soundcard). Be interested if anyone else has had
success this way, or has my CD player indeed knobbled the SPDIF output?

Anyway, the HDCD patent 5479168 says this,

"The command codes and other auxiliary data are encrypted with a
pseudo-random noise and inserted into the least significant bit of the
main signal digital words in a serial fashion, one bit per word. The LSB
of the audio is replaced by a "random" noise for the duration of the
control insertion. (Of course, more than one bit could be "borrowed" for
this purpose, but more of the main program would be lost.) The system is
set up so that when the control channel is not needed, the LSB carries
the normal audio signal. Since the digital to analog converters in most
of the current generation of digital audio products are not accurate to
16 bits, the loss of the 16th bit will not be audible during undecoded
playback, as long as the information inserted there has noise-like
properties. Even in high quality systems which do resolve all 16 bits,
the insertion is not normally audible because the LSB of most programs
already has very noise-like properties. The low level gain compression
and dynamic dither described previously raise the level of the program
during very quiet periods and help hide the code insertions during those
program conditions under which they might be noticeable. In typical
classical music programming, the control signal would be inserted for
intervals of about a millisecond each occurring several times per second
at most. The loss of full program resolution for these brief intervals
is not noticeable."

So far as I know, I have no HDCD discs

I find HDCD discs on sale in strange places. Like Poundland[1] for a
quid! Maybe the logo 'HDCD' has confused normal CD purchasers. If you
type in www.hdcd.com you will notice Microsoft is also confused how to
promote the technology (no relevant page linked!)

[1] - http://www.poundland.co.uk Recommend 'Sophie B. Hawkins - Timbre'
but mind some of her F'in language... Also 'Simple Minds - neon lights'
on sale there is a HDCD disc (but one that sounds identical HDCD decoder
on or not[2] - and Simple Minds have rather lost their magic anyway...)

[2] Turned 'off' by the 16-bit via SPDIF copy method. My CD player does
not have a HDCD decoder defeat switch.

--
Adrian C

HDCD re-encoding
 

"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.

HDCD re-encoding
 

Jim Lesurf wrote:

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!)

The effect seems to be one of a compander. Another post mentioned
something about soft peak limiting, which would resolve with the
observed effects. Many HDCD discs sound squashed dynamically when played
on a non-HDCD player.

More generally, though, I find that provided I avoid problems like
clipping, that the sound when I replay a CD I have recorded from an
analogue source sounds to me just like the source I recorded. Hence
I'd be inclined to expect this of the analog from an HDCD player as
well... But this is simply an expectation, not an actual result. :-)

Well... I've now bought myself a Sony RCD-W100 CD recorder. (Needed it
for some other work archiving historical recordings to CD without
requiring the use of a PC.) And have done a few tests.

An analogue copy of an HDCD disc with SBM (Super Bit Mapping) turned on
does indeed sound just as good as playing the original via analogue (and
sounds a damn sight better than playing the disc with no HDCD decoding).
With SBM turned off you can distinguish between original and copy, but
only back to back.

According to the manual SBM uses "a form of noise shaping to encode an
effective resolution of 24 bits into the 16-bit medium". Whatever the
jargon, it works - analogue recordings made from HDCD do sound more
detailed.

--
Glenn Richards Tel: (01453) 845735
Squirrel Solutions http://www.squirrelsolutions.co.uk/

IT consultancy, hardware and software support, broadband installation

HDCD re-encoding
 

In article , Arny Krueger
wrote:

"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.

Thanks. I'll have a search for it when I get a chance. :-)

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.

I've seen descriptions along those lines before, but none that gave any
detail... until Adrian's and your own postings later in this thread!

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.

Indeed. Also, since we can expect well-recorded examples to have used some
form of noise shaping, the 'vanilla' CD spec may well provide a better
audible performance than is required even for signals with a wider range.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html