From: olson@anchor.esd.sgi.com (Dave Olson)
Newsgroups: rec.music.synth,comp.dsp,comp.sys.hp,comp.sys.sgi
Subject: Re: AUDIO-CD READING ? [ some answers from an SGI'er ]
Date: 30 Aug 92 00:53:06 GMT
Organization: Silicon Graphics, Inc.  Mountain View, CA

I think I'm covering most of the questions here; I didn't want to
respond to each individually.

The SGI drive is a modified Toshiba 3301B.  It has custom firmware and
custom hardware.  Sony also did a similar drive for our evaluation.
The hardware mods were required because the data stream was split very
early in the hardware, and there was no way to sync up the subcodes and
the digital audio data without the hardware mods; it was also necessary
to suppress the 3rd level ECC, which wasn't possible with the original
hardware, and we wanted to prevent the drive from doing interpolation
when ECC couldn't correct the data on errors.

The firmware mods were largely in the definition of new commands to do
the setup and data transfer of the audio data, as well as the format in
which it is returned over the SCSI bus.  That was one of the more time
consuming parts of the development of the capability.

I believe both Sony and Toshiba have announced that they intend to
support reading audio (red book) CD's on their next generation drives
(the dual speed ones), at least, as an option.  As far as I know,
Toshiba and Sony do not sell the current drive to anyone else, although
there are no contracts forbidding them from doing so.

One of the big differences between taking the AES output (from drives
that have it), and reading the digital data over the SCSI bus is the
presence of subcode Q info, which gives you position info, among other
things.  The newer drives will provide (or are supposed to!) all the
subcodes.

It is possible that the SGI drive will work on Sun's, for booting,
software installation, and ISO-9660 filesystems, since the reverse is
true (for at least some drives Sun ships).  Whether this is true with
the HP drives, I couldn't say.  SGI has the same sort of hack that Sun
has, for similar reasons (the drive powers on default to 512 byte
logical sectors, so old CPU PROMs can read the media).  The SGI drive
has an additional hack; after power on or SCSI bus reset, the inquiry
info claims that the CD-ROM is a hard disk drive (type 0 direct access,
non-removable media), as our older (but not current) CPU PROMs checked
for this.  The normal inquiry info (but still 512 byte logical blocks)
is returned after the 10 byte vendor-specific SCSI command 0xc9
followed by 9 0's is issued.  I don't know how the HP PROMs will react
to this, since they are reasonably new, and may expect CD-ROM drives to
identify themselves as such.

There may have been some paranoia at one point on the part of the
CD-ROM drive vendors about allowing the raw audio data to be read from
the drive, but our vendors told us that the drives were designed as
they were to simplify the logic on the drive, not as a deliberate
method of keeping people from reading red book CD's.  There was one
other large vendor who requested similar abilities for reading audio
CD's over SCSI, at the same time SGI was, but they backed out.  Prior
to that, the drive vendors said that they had not had any serious
requests for the capability.

As somebody else said, the data rate is low enough that just about any
workstation or high-end PC should be able to handle it.  Applying the
emphasis (another piece of info in the subcodes) that is sometimes
needed could prove taxing to some of the PC's though.  Finally, if you
don't have 16 bit hiqh quality audio on your workstation, or on an add
in board, there doesn't seem to be a whole lot of point in bothering.
We do have that, and we also have software that allows you to do some
limited mixing and editting, as well as libraries that allow
users/developers to write more sophisticated apps.

I think that I've covered about all the questions that were asked
(there were about 40 articles in the thread, so I could have missed
something).  If you have further questions about the audio capabilitis
of SGI's CD-ROM or DAT drives, please include comp.sys.sgi, as I don't
get to comp.sys.hp all that often (and almost never to the other
newsgroups in the list).  I've added comp.sys.sgi to the Newsgroups
list on this one.
--
Let no one tell me that silence gives consent,  |   Dave Olson
because whoever is silent dissents.             |   Silicon Graphics, Inc.
    Maria Isabel Barreno                        |   olson@sgi.com