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Software HDCD Decoding?
Toshito asks: "I found that I have several CD's with HDCD encoding. I understand that these CD's contain a 20 bits stream encoded in the 16 bits (the original signal is truncated at 15 bits). A standard CD player will play the 15 bits version, but you have to get a HDCD compatible player to access the 20 bits version. My question is: do you know of any way to decode this stream on a computer with software only? Is the decodind method secret and only available in chip (hardware) form?"
Windows Media Player 9 as it comes with Windows XP supports HDCD number of other technologies such as SRS.
If you want to write your own talk to Microsoft about licensing it, as they purchased Pacific Microsonics(makers of HDCD) several years ago.
HDCD, while developed by a high-end audio company whose name currently escapes me, is now 100% owned by (you guessed it!) Microsoft along with the aforementioned original developer.
It is also patented.
You can find an overview of how things work during the encoding process here, but don't expect anyone to tell you how to do any of those things without you first handing them vast fistfulls of cash.
You might be able to glean some useful information from the patent text, but probably the only sane way to go about this effort would be to read the bitstream coming from the CD. And while you should able to discern what the bitstream looks like without too much effort, it would probably be a fairly involved task to learn what it means.
So. My only suggestion would be to give up now before you've wasted any effort on trying. But if you insist on putting real time into this project, here's a couple of nice encapsulated postscript HDCD logos you can illegitimately use to adorn any illegitimate HDCD products you produce.
Kid-proof tablet..
Unless you're using some really amazing audio hardware, I wouldn't bother. Most any equipment you'd want to hook up to your PC will not be able to give the full dynamic range of the 16-bit signal, much less the HDCD audio. Most sound cards you use won't be able to either, and that includes ones with SPDIF output. Not to mention, once you encode to Ogg or MP3, all that extra quality goes out the window.
Ripping tools may be desirable when they start putting "exclusive content" on the HDCD layer only, or start making them without the compatibility layer, but there's nothing like that in the pipe, so far as I know.
Like albums and Dolby noise reduction cassettes, there are complementary filters for encoding or decoding; it's just more complex than an equalization.