HDCD rip - how ?

[DSPguru]

i need info about HDCD.

HDCD is a new way (two years or so..) to store 44.1khz/20bit samples on a Audio-CD.
HDCD if fully backward-compatible, so all regular players would read 44.1khz/16bit.

i bought the latest album of Sprituazlized (http://www.spiritualized.com/f_index.html) , and it's HDCD.
i can truely feel that the quality is Higher, and enjoy that very much (i wish the composition was as good as the sound quality ;)).

my question :
1. does anyone know how, physically, HDCD works ?
2. how can i rip those 20bit tracks ? i guess there are HDCD-compatible cd-roms that can do that, but mayB i could image the CD, and demux it offilne. any ideas ?

[-h]

Honestly it sounds like HDCD's improvements are just due to the sound engineers doing a better job at mastering the CD. Some of the claims - squeezing 4 LSB's into 1, 20-bit audio sounding noticably better than 16 bit, the HDCD decoder making other digital sources sound "better", etc. - are pushing what I would call believable.

I'd say just rip the songs in the usual fashion. It smells like SACDs all over again - same old 16-bit audio, just with better mastering practices being enforced.

The engineer in charge of mixing the CD makes a *much* larger difference to the final quality than the sample resolution.

-h

[LigH]

It is hard to find any valuable information from http://www.hdcd.com - my current guess is that some kind of dynamic compression, pre-amp, dithering or similar technologies are used. To be compatible to older CD players, requires the data to be 16 bit per sample. In the Audio CD sector format is not much space for additional information, maybe someone can find a way to store a few bits per sector as base amplification level in mostly unused bits of the sector header. But there is definitely no room for 4 bits per sample.

I could not yet read it deeply, but the following link may contain more details (found "by accident" while searching for the Audio CD sector format):

http://www.meridian.co.uk/ara/araconta.htm
_

An additional short note was found here:

http://www.disctronics.co.uk/cdref/cdaudio/hdcd.htm

It seems that really only the least significant bit of the 16 bit data contains information about 5 least significant bits of the 20 bit original. Sounds hard to believe. I want a listening test with very soft classical music...

[Gabriel_Bouvigne]

If you use a regular cd player, you won't have the maximum benefit of HDCD.
What you'll have is basically a dynamically compressed cd with a little dithering.
An hdcd decoder will allows you to decode the full dynamic range. But this doesn't really give you 20 bits. It's similar to 20 bits, but you don't really have some 20bits pcm samples on this cd.

[DSPguru]

Originally posted by Gabriel_Bouvigne
If you use a regular cd player, you won't have the maximum benefit of HDCD.
What you'll have is basically a dynamically compressed cd with a little dithering.

my home-player plays HDCD and it's great.

An hdcd decoder will allows you to decode the full dynamic range. But this doesn't really give you 20 bits. It's similar to 20 bits, but you don't really have some 20bits pcm samples on this cd.
so what IS it ? what's the system ?

[Gabriel_Bouvigne]

Let's assume that you understand the fact that 20 bits give you more dynamic over 16bits, or better resolution if you decide to keep the same dynamic.
Here is the trick:

The master is dynamically compressed from 20bits to 16bits in order to fit on the regular cd.
From time to time, the least sigificant bit of the sound is used not for music but for additional data. This data indicate how to reconstruct the dynamically compressed part in order to retrieve the original dynamic range (20bits-like). This bit is used about 30 times by second.
So on a regular cd player, 30times per second you've got one modified bit. If you keep in mind that you've got 44100 samples per 2 channels, modifying the last bit of 30 of those samples is quite insignifiant and does not degrade the sound.

[DSPguru]

Originally posted by Gabriel_Bouvigne
Let's assume that you understand the fact that 20 bits give you more dynamic over 16bits, or better resolution if you decide to keep the same dynamic.

hehehe :)

Here is the trick:

The master is dynamically compressed from 20bits to 16bits in order to fit on the regular cd.
From time to time, the least sigificant bit of the sound is used not for music but for additional data. This data indicate how to reconstruct the dynamically compressed part in order to retrieve the original dynamic range (20bits-like). This bit is used about 30 times by second.
So on a regular cd player, 30times per second you've got one modified bit. If you keep in mind that you've got 44100 samples per 2 channels, modifying the last bit of 30 of those samples is quite insignifiant and does not degrade the sound.

is this info stored in one-bit that interpolates an exponential-gain in sigma-delta format ? or this bit is being collected to a N-bits WORD with gain information ?

where can i d/l info about it ?
i want more info, 'cause the method you mentioned above can be implemented on a PC, meaning i can "rip" HDCD discs.

[Gabriel_Bouvigne]

I don't know what to do with this bit, neither when to catch this bit, sorry.

I had to grab the whole hdcd.com website before beeing able to know the only little piece of info I have.

If you want some further information, perhaps you could search in aes publications, or in patent databases.

[mpucoder]

I guess you really want to expand it back to 20-bits, right? That would be neat, I wish I could find some info on their method as well. As for ripping it and burning to another CD, it should work the same as a regular CD, from the description I read. Good thing they didn't use one of the unused sub-channel bits, as CD+G did, that would be a real bitch to rip. (And one sub-channel bit provides 75 bits/second, more than the 30 required - but maybe placement is more critical than just every 1/75 second)

[DSPguru]

idea
if we knew how HDCD works, we could create our own HDCD cds with music ripped from DVDs.

[Gabriel_Bouvigne]

It's a long time since I've come to hdcd.com.
I just discovered with horror that Microsoft bought the hdcd technology.

[ChristianHJW]

... isnt HDCD about to die, now with SACD and DVD-Audio being out ??

[Kandor]

about cd to die.
that what they said about the venyl when cd came out.
and not even today with sacds or dvd audio can they beat the good old venyl.
I know alot of ppl are going to flame me now but if you have listened to a Linn Sondec LP12 then you know what I mean, and if you havent then your going to flame me.
and for the SACD and DVDaudio.
have you heared the Linn sondec CD12? even that source sounds better than the sacd atleast havent compared it to dvd audio thou.
havent even heard it but anyway.
because of the cd12 to be able to reproduce better sound from a regular audio cd than sacd does from sacd sony have even started to get help from Linn to produce sacds in the future and when they will come out with a player then I will belive that cds maybe is going to die but not now.


and if you dont belive me please visit a linn retialer and listen for your self. and please no comments about the bits here and bits there.
just listen and judge by your self.


Best Regards
Kandor

[Kandor]

It seems that the cds are pressed in the old fassion way, because I tried to copy a hdcd cd and the copied cd played with hdcd enabled.

[Fox Mulder]

http://www.hdcd.com/partners/proaudio/articles.html

http://www.hydrogenaudio.org/forums/showthread.php?threadid=591&highlight=HDCD

[DSPguru]

http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=/netahtml/srchnum.htm&r=1&f=G&l=50&s1=5,479,168.WKU.&OS=PN/5,479,168&RS=PN/5,479,168