The first units
to adopt GM Level 2 are from Roland, interestingly enough, and are the
latest models in their Sound Canvas line, which started the whole General
MIDI movement; and Korgsurprisingly, in its high-end Triton rack.
More are expected to follow. Be sure to check out the product intros at
winter NAMM this month.
But things are happening at the other end of MIDI, toothe professional
end. The lowly MIDI cable, with its 31,250-bit/second speed, is ridiculously
slow compared to todays networking and busing capabilities, and
that fact has not been lost on the MIDI developer community. While MIDI
over SCSI never was practical (SCSI is fast, but it works in spurts, which
is okay for buffered digital audio, but not okay for the real-time control
that MIDI requires), there have been strong efforts to incorporate MIDI
with the newest networking protocols: USB and IEEE-1394, or FireWire.
USB MIDI interfaces have been around since early 1999. After Apple released
the first USB Macintoshes, manufacturers like Emagic, Roland, Steinberg
and Mark of the Unicorn scrambled to put out USB-compatible MIDI interfaces.
Now there are a dozen or more on the market, from simple palm-sized 1-in,
1-out boxes to rackmount multicable interfaces with SMPTE and audio I/O.
Happily, a standard method for putting MIDI on a USB cable is defined
by the USB Implementers Forum (USB-IF, www.usb.org).
Unhappily, the MIDI Manufacturers Association never endorsed the USB MIDI
specand youll see why in a moment.
USB has been very successful in replacing, or at least displacing, many
of the disparate computer-networking formats like serial, parallel, PCI
or SCSI ports. Printers, modems, scanners, removable media drives and
gadgets we didnt even know we needed just a couple of years ago
are now using USB cables. There are great advantages to USB, such as the
ability to connect up to 127 devices of all kinds to a single computer
(using bridges and hubs), automatic configuration (no more IRQ or SCSI
ID nightmares), the ability to hot-swap devices, and higher
potential throughput than any of the formats it replaces, with the exception
So whats the problem
with MIDI? According to Jim Wright at IBM Research, a longtime member of
the MMA Technical Standards Board and chairman of the organizations
working group concerned with new transports, USB has timing problems that
make it problematic for MIDI. He has conducted tests comparing classic
(i.e., serial, parallel, PCI or PCMCIA) interfaces against USB interfaces,
looking at their round-trip latency (the amount of time it takes for a MIDI
event to get in and out of the interface) and their jitter (the variation
in the latency). He found the latency in the USB interfaces to be between
seven and eight milliseconds, about three times that of the classic interfaces.
This is not in itself an insurmountable problem, because musicians adjust
to small latencies in sound sources quite wella bass player and a
lead guitarist standing seven feet away from each other usually have no
trouble staying together.
of these solutions are compatible with each other, which negates
the entire philosophy of MIDI and USB.
But the jitter in USB interfaces was also much higher than the older interfacesabout
twice as high, meaning (to continue our analogy) that the two players could
at any given moment be five feet away from each other, and the next moment
be 10 feet awayand constantly moving. In another analogy, which Wright
likes to use, imagine playing a slightly arpeggiated guitar chord: The jitter
could make it sound as if one of your fingers jerked slightly while you
were playing the chord. And for tight grooves and thick MIDI data streams
with lots of aftertouch or controllers, this level of jitter is really unacceptable.
Wright also found that when you add audio to the USB stream, the jitter
goes up another 50%so its three times what MIDI musicians have
had to deal with in the past.
Magazine, January, 2001
© 2001, Intertec
Publishing, A Primedia Company All Rights Reserved
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