Into the New Millennium With…?

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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 Korg—surprisingly, 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, too—the professional end. The lowly MIDI cable, with its 31,250-bit/second speed, is ridiculously slow compared to today’s 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, Unhappily, the MIDI Manufacturers Association never endorsed the USB MIDI spec—and you’ll 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 didn’t 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 of SCSI.

None of these solutions are compatible with each other, which negates the entire philosophy of MIDI and USB.

So what’s the problem with MIDI? According to Jim Wright at IBM Research, a longtime member of the MMA Technical Standards Board and chairman of the organization’s 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 well—a bass player and a lead guitarist standing seven feet away from each other usually have no trouble staying together.

But the jitter in USB interfaces was also much higher than the older interfaces—about 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 away—and 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 it’s three times what MIDI musicians have had to deal with in the past.


Reprinted with permission from Magazine, January, 2001
© 2001, Intertec Publishing, A Primedia Company All Rights Reserved