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From: dave@onfcanim.UUCP
Newsgroups: sci.electronics,rec.audio
Subject: Decoding of CD player "digital out"
Message-ID: <15368@onfcanim.UUCP>
Date: Sun, 16-Aug-87 01:30:45 EDT
Article-I.D.: onfcanim.15368
Posted: Sun Aug 16 01:30:45 1987
Date-Received: Sun, 16-Aug-87 13:46:27 EDT
Organization: National Film Board / Office national du film, Montreal
Lines: 29
Xref: utgpu sci.electronics:1052 rec.audio:2403

I'm looking for information on how to extract the data from the
signal that is fed to the "digital output" jack of my Philips (Magnavox)
CDB 650 CD player.

Looking at the signal on an oscilloscope, it appears to consist of a framing
pulse, and then a block of bits transmitted using a simple modulation
technique.  I want to know:

  1) how to build a circuit that will find the framing signal and then
     demodulate the data into an N-bit parallel word plus strobe ready
     to be connected to a computer parallel interface

  2) how to interpret the various bits that I get from this.  Most of them,
     of course, are audio data, but there should also be an "uncorrected
     error" flag, and maybe subcode information.

  3) how to build a simple FIFO buffer to sit between the decoder
     circuitry and the "host" computer, since the computer
     will accept data in bursts.

The idea is to obtain high-quality digital audio to experiment with
(e.g. using the Fourier transform to look at the frequency spectrum)
without the cost of analog-to-digital conversion hardware.

I'd appreciate pointers to code standards, circuitry, or anything else
that seems relevant.

	Dave Martindale
	{watmath,musocs,micomvax}!onfcanim!dave