I seem to recall that there is a freebie HDCD decoder kicking around. What
does it do?

"Jim Lesurf" wrote in message
...
On 15 Jun, wrote:
In article ,
wrote:
Email address here?

http://dvdid.cjkey.org.uk/

Paul

Thanks! :-) I'll send him an email.

I've not had - as yet - any reply to the email. But in the interim I've
been doing some experiments trying to de-spread the LSB coding on three
discs with HDCD logos.

The Patent says the LSB control uses a maximum length sequence spreader
and gives as an example the (5.3) example. It also says the sequences are
39bit inc. a check. Which is consistent with (5.3) as that gives a 31 bit
pattern, so 39 could be the pattern plus a check byte.

To test that I wrote both an MLS encoder and matching decoder. These work
when I use one to feed the other, as per the textbooks.

One of the documents I've found about an HDCD ADC/recorder says that
recordings should start with about 100 ms of 'hdcd silence'. i.e. no audio
and a place to put a control pattern which the player/dac can then
unambiguously detect.

So I've tried the decoder on some discs. But this doesn't seem to give an
identifiable result. On one disc there is no such 'silence'. On others
quiet part seems to use the lowest *three* bits of samples. Not just the
LSB.

So I'm coming to the conclusion that this may be another example of how
the
patents and public documents simply obfuscate and don't actually tell
anyone what hdcd does (or doesn't!) or how.

I'll experiment when I get a chance with other MLS encoder/decoder pairs,
and perhaps do some correlations to see if I can pull patterns out of the
LSBs. But the more I examine HDCD the more dubious I get about both
regarding them as 'audio CDs' and the validity/reliability of the Patents,
etc. Increasingly looks like hype with the occasional use of a peak soft
limiter!

Slainte,

Jim

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