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This Network Rocks
Gibson Labs has found a way to send real-time audio over Ethernet, and music may never be the same
Joseph Ogando, Senior Editor -- Design News, March 2, 2003
Forget about the sex and drugs. Rock and roll may soon be fueled by bits, bytes, and bandwidth. At least, it will if the engineers from Gibson Labs (Sunnyvale, CA) have their way. Over the past three years, they have applied their technical chops to creating networking standards and hardware that can transport real-time audio over ordinary Ethernet cables. Early this year, they built a groundbreaking digital guitar that marks the first use of this new communications technology. And with all due respect to old-school rockers—who are still free, by the way, to partake of whatever stimulants they please—this new instrument may represent the biggest change in the way guitarists plug in since electric guitars first appeared more than 70 years ago.
Musical instruments don't usually get the same engineering attention as cars, planes, medical devices, and other high-tech products. And for good reason. "Guitar making is still very much a wood and glue business," admits Jeff Vallier, a senior audio hardware engineer at Gibson Labs, the technology group for the Gibson Guitar Corporations. His company, however, has a storied history of technical innovations dating back to 1894, when Orville Gibson began building acoustic guitars with violin-like arched tops. This guitar maker's latest foray into audio hardware systems may even have implications in the industrial world. "We see the Gibson standard primarily as a way to move audio from point A to point B in a cost-effective way," says Barani Subbiah, director of non-personal-computer business for networking equipment giant 3COM (Sunnyvale, CA). Yet he hastens to add that the standard could work in industrial automation and control settings too. "It has a lot of good features that could come into play on the shop floor," he says.
It turns out that Gibson's approach to real-time audio addresses two crucial real-time data transport problems. One relates to improving quality-of-service, or the network's ability not to mishandle data. "The human ear is extremely sensitive," Vallier points out. "The average listener can hear even a very small amount of dropped data." At 48 KHz sample rates, for example, even a single dropped data packet can turn up as an audible—and not very musical—click. Then there's the latency problem. Vallier dryly points out that musicians have this expectation that "what they play and what comes out of their amp will somehow sync up." Real-time audio simply can't tolerate sluggish data transport.
Gibson's MaGIC specification addresses both these problems. Short for "media-accelerated global information carrier," MaGIC allows ordinary 100-Mbit Ethernet cable to carry up to 32 channels of 32-bit bi-directional audio with sample rates up to 192 kHz. "It doesn't drop any samples at all as far as we can tell," Vallier says. "The sound is pristine." And it's faster than a speed metal guitarist. According to Vallier, this real-time system guarantees a point-to-point latency of just 250 microseconds across 100 meters.
It's worth noting that MaGIC is not some enhanced form of MIDI, the 20-year-old "musical instrument digital interface" standard. MIDI sends instrument control information, such as note duration and pitch, over a serial connection, but "doesn't send audio signals at all," Vallier emphasizes. Anyway, MaGIC's 64 channels can also transport control signals—including MIDI—just as easily as they can move audio, only faster. Vallier reports that MaGIC currently clocks in at about 300 times faster than a typical MIDI system.
MaGIC Tricks
To make Ethernet faster and more reliable, Gibson engineers first took a hard look at the standard OSI networking model with its seven-layer stack of communication protocols—and promptly disregarded almost all of it. MaGIC and conventional Ethernet systems share only the physical layer that consists of specifications for electrical and mechanical connections. Both use standard CAT 5 cable and RJ 45 jacks, for example. "But everything above that physical layer is our own protocol," he says. Nathan Yeakel, Gibson Lab's chief technical officer, adds that the company's early efforts tried to use usual high-level Ethernet protocols—an IP backbone, for one. But these required constant buffering and re-sampling of audio data. "It couldn't guarantee the latency or quality of service we needed," he says. The MaGIC protocol does provide these all-important guarantees. In part it does so with the aid of a custom media access controller and software that encapsulates audio data in efficient fixed-length packets and sends that data over the network at a pre-determined sample rate.
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Sound system: Gibson uses MaGIC, a networking communications standard to transport real-time audio signals over an Ethernet backbone. |
In keeping with Gibson's goal of making MaGIC a standard, it runs on any number of hardware platforms and can take advantage of ongoing Ethernet developments—such as the move to 1Gbit/sec data transmission rates. "MaGIC is completely physical-layer independent," Yeakel stresses. For now, the MaGIC hardware developed at Gibson Labs consists of two boards. The MaGIC "engine"—an Analog Devices DSP and Xilinx field-programmable-gate array (FPGA)—runs on one board. And a separate board designed by Gibson engineer Mike Dibble holds all the electronics needed for audio-to-digital conversion tasks. Andreas Schmidt, the Gibson engineer responsible for FGPA programming and ASIC design, says that Gibson could just as easily introduce an ASIC-based version of MaGIC. "It all depends on our volumes," he says.
3COM has already taken this route. The company has developed its own single-chip MaGIC engine based on an ASIC with the custom MAC embedded in it. Subbiah reports that 3COM will soon offer its MaGIC chip to a wide variety of music and audio equipment OEMs—including those who make keyboards, speakers, recording equipment like mixing boards, home audio systems, and large theater- or stadium-sized sound installations. "We've had a lot of interest already from a variety of audio equipment makers," he says.
All these audio systems can benefit from MaGIC's most obvious advantage—drastically simplified wiring. Professional users can replace their "audio snakes," thick bundles of analog cables that cost hundreds of dollars, with "a $10 Ethernet cable that you can pick up at K-Mart," says Vallier. Consumers could get rid of the bird's nest of wires behind their home theaters. And with its low latency, this wiring system conquers long distances. "You can run a cable over 2,000 meters with no loss of audio quality," Vallier says. All sorts of users could also take advantage of the systems plug-and-play nature. With the MaGIC network automatically recognizing each hardware device plugged into it, users could configure complex sound systems from a single personal computer—much in the way a network administrator lords over you LAN in the office. Vallier predicts that third-party software developers will come out with graphical software to simplify this task. A rock band, for example, may one day be able to set up their sound from the stage simply by dragging and dropping icons.
Not surprisingly, the first to take advantage of the standard is an electric guitar. At the Consumer Electronics Show in Las Vegas in January, Gibson Labs showed off its first digital guitar, based on 3COM's chip. All the MaGIC electronics fit in a "break out" box that installs in a pocket in the back of the guitar. About the size of a paperback, the box takes up more room than many guitar players would like. But Vallier reports that the design team already has miniaturization plans in the works that should bring the electronics package down to something smaller than a pack of cigarettes. "The production system will ultimately fit in the standard pocket already found in electric guitars, so they won't need any extensive modification," he says.
Sweeter Sounds?
The digital guitar retains Gibson's classic "humbucking" pickup—the magnetic transducers that translate string vibration into an electrical signal. Keeping this pickup is central to the guitar's acceptance because it gives technophobe guitarists the option of playing their digital guitars as they always have. "The signal path of our Les Paul guitar is 100% intact," says Yeakel. "We wouldn't mess with that sound. It's our bread and butter." But the digital guitar also sports a new pickup that complements MaGIC. This patented hex pickup differs from traditional models in that it senses both up-and-down and side-to-side string motion—while earlier pickups focused on one motion or the other. And it employs powerful neodymium-iron-boron magnets rather than the usual ceramic magnets. According to Yeakel, this magnet upgrade helps improve isolation between strings and results in a pickup with better frequency response (80 kHz) and dynamic range (96 dB). "That's best available in audio today," he says. The system also stands out because it takes care of the analog-to-digital conversion inside the guitar, very close to the pick-up. "We have a totally digital backbone for our system," Yeakel says. "Some earlier digital music systems look more like islands of DSP in an ocean of analog." Doing all the A/D conversion in the guitar itself fights all sorts of threats to sound quality, including noise from the analog cabling, stray frequencies from the pickups, and errors introduced during multiple A/D and D/A conversions. "We end up with a much clearer tone," he says.
Taken together, MaGIC and the new pickup could bring some interesting sonic possibilities to the electric guitar. MaGIC and the pickup process the signal for each string separately and assign each one its own output channel. So the system can give users the flexibility to adjust volumes, distortion, and any other effect string by string. Musicians can map individual strings to different amplifiers for a truly custom sound. Or they can even assign different effects to the existing knobs on the front of the guitar. The new pickup gives MaGIC a lot more raw string data to manipulate in the quest for new or improved sounds. Yeakel envisions a future where this extra string data results in improved emulation of other instruments, for example. "You might have the guitar sound just like a banjo or dobro with the flip of a switch," he says.
With only four prototypes built so far, not many guitarists have had a chance to hear a digital guitar—much less put it through its paces. Vallier points out that some have complained anyway. "Musicians are extremely wary of new technology," he says. "And this is as new as it gets." But some guitarists have recognized the potential of digital guitars to move beyond ordinary MIDI. "MIDI has always been more popular with keyboardists, but it has had limitations in the context of the guitar," says Rick Peckham, assistant guitar chairman at the Berklee College of Music (Boston). He cites excessive latency and a less than warm tone as two of the MIDI downsides that turn off many guitarists. "It's really tough to maintain the integrity of the sound through all the processing," he continues. But if Gibson's digital guitar does deliver on its promises, Peckham says he would give the system a try in a downbeat. "It all sounds very appealing to me," he says.
