🚀 go-pugleaf

Hello everybody!

I'm planning to build some fancy digital audio equipment and
would like to use the optical digital output from the Alesis
ADAT. This output carries 8 audio channels on one optic fiber
and is probably not standardized.  I probably have to call
Alesis for any info on the format used but I also would like to
hear comments from anyone on the net who has info/experience
about this interface. Could I perhaps use S/PDIF chips running
at 8x speed to decode the format?

I'm also interested in the S/PDIF and AES/EBU formats. I don't
like to pay lots of $$$$$ to buy a thick book with a couple
of useful sides with the formats explained - so I use the scope.
This is what I discovered by monitoring the S/PDIF output with
an o-scope:

   Sample rate:           44100 Hz
   Frames/sample:             2         (left frame, right frame)
   Bits/frame:               32         (64 bits per sample)
   Bit rate:          2 822 400 bits/sec
   Transmission coding:   Bi-Phase Mark (Harvard-FM)

Frame format:

  left frame:  0101 0000 0000 xxxx xxxx xxxx xxxx ab0c
  right frame: 0110 0000 0000 xxxx xxxx xxxx xxxx ab0c

                x = audio data bits,  16 bits/frame
                a = changes 1/0 in pause mode
                b = changes 1/0 always
                c = checksum bit (restores signal level to zero)

The first four bits are obviously some kind of frame synchronization
bits and are coded differently from the other (without bit clock?
NRZ-FM). There seems to bee 8 extra (subcode) bits in a frame!

I would like to know what the functions of bits a and b are. Has
the b-bit something to do with SCMS?

Mail me corrections and more info if you have it and I'll summarize
here the complete format specs (or is this a FAQ?).

  Thank You!
  

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+       Tom Ahola     tahola@otax.tky.hut.fi  (128.214.8.1)            +
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