Subject:	AES/EBU  and  SPDIF  ???
From:	"Roger Mielke" <museum@cybcon.com>
Date:	8 Nov 1997 23:29:21 GMT

I have a question regarding  AES/EBU is this a protocol or a wireing type
as far as digital i/o gies.
Same with SPDIF, is it a protocol or cable type requirement ?
I would like to get this striaght with myself, any input would be nice.
Thanks

From:	bkingman@interport.net:
Hey Roger, There is a difference in the way each format handles
information, and they are NOT interchangeable.
I'm not a digital guru, but I will tell you what i do know. Besides the
obvious connector issue (XLR vs RCA) when makeing digital dubs via 2 dat
machines, the spdif format transfers all of your start ID's along with
your audio. The AES format does not. I found this to be quite a drag when
copying 2 hour live shows with many start ids.

From:	mrivers@d-and-d.com (Mike Rivers):
Both.  The standards define data formats for "Professsional" (AES/EBU)
and "Consumer" (S/PDIF) systems, as well as the phyisical interface
(wiring/cable type).
The AES/EBU data word contains 20 bits for digital audio, four
"auxiliary" bits, four "Channel Status" bits, and some sync bits.  The
channel status bits tell the receiving system what kind of data is
coming in and what the auxiliary bits are being used for.  Those aux
bits can be another audio channel (not a very high quality one),
control or signalling data, or even something like copyright
identification.  Sometimes they're not used at all, but with the
proliferation of 24 bit A/D converters, manufacturers are starting to
use them to extend the audio data word to 20 bits, ignoring the
specification.  
The original AES/EBU spec called for a differential output at 110 ohms
characteristic impedance.  The current AES-3 spec calls for a single
ended 75 ohm output, a blessing because that's commonly available
cable.
The S/PDIF standard uses a similar word (which is why, to a great
extent, you can copy one to the other digitally by adapting the
physical interface) but there's no standard for audio data word
lenght, and the channel status bits have different meanings.  The only
thing they have in common is the bit which tells the receiver if it's
a pro or consumer format so it (hopefully) knows how to interpret the
other bits.
S/PDIF has physical interfaces defined both for a coaxial and fiber
optic connection.

From:	Tomi Holger Engdahl <then@tinasolttu.cs.hut.fi>:
The connectors are 3 pin XLR connectors (same as used with microphone
signals and other balanced audio connections). The cabling is shielded
twisted pair wiring (microphone cabling) with characteristic impedance
of 110 ohm.
The most typical connector for SPDIF signal is RCA connector, but
sometimes BNC connector is used. The cabling is 75 ohm coaxial
cable (same that is used for vidoe signals).
More information about S/PDIF can be found at
http://www.cl.cam.ac.uk/Research/SRG/HAN/docs/sp-dif.txt
http://www.hut.fi/Misc/Electronics/docs/audio/spdif.html

From:	scott@basis.com (Scott Amspoker):
It's easy to get confused about these two standards since the line
between them is sometimes blurred by digital audio devices trying to
be flexible.
AES/EBU normally uses 3-pin XLR connectors, at 110 ohm output
impedence, and a specific data packet format.  SPDIF normally uses
cables with RCA connectors at 75 ohm impedence (or optical cable) and
has a slightly different data packet format.
It's not unusual to find digital audio devices that accept either data
format on its inputs regardless of the physical characteristics of the
connector.  In other words, a device might have XLR jacks but will
accept SPDIF data format as well as AES/EBU.
Strictly speaking, it is best to regard them as two different formats
in both hardware and software.

From:	shlampen@aol.com (ShLampen):
And then you can buy a balun to convert from 110-ohm balanced to 75-ohm
unbalanced which means you can indeed have the AES format in coax and have
an SPDIF format right next to it on an identical coax.  i.e. just because
it's on coax means it could be EITHER.  Right?

From:	"MIKAEL THIEME" <mikael.thieme@swipnet.se>:
> And then you can buy a balun to convert from 110-ohm balanced to 75-ohm
> unbalanced which means you can indeed have the AES format in coax and
> have an SPDIF format right next to it on an identical coax.  i.e. just because
> it's on coax means it could be EITHER.  Right?
Perfectly right.


