Not so long ago, a self-tuning guitar was simply one you tuned yourself. Gibson’s latest electric guitar, however, really does take tuning out of the guitarist’s hands and tunes itself with servo mechanisms and control algorithms that dynamically adjust string tension.
This Robot Guitar grafts a Powertune automatic tuning system from Germany’s Tronical GmbH onto a version of Gibson’s Les Paul electric. The system makes tuning trivial, whether the guitar player is working with the standard tuning or not.
To kick off the tuning process, the guitarist pulls out a control knob, strums the strings and waits for the servo-driven tuners to bring the guitar in tune. And unlike a guitar player, the Powertune system can adjust the tension of all six strings simultaneously. It usually takes just a few seconds to bring the guitar into tune, with the exact amount of time depending on the difference between starting and ending pitch of each string. The system also remembers as many as six alternative tunings, both user-defined and pre-set, allowing for quick changes out of standard tuning.
Aside from making tuning fast and easy, the Robot Guitar also promises to improve absolute tuning accuracy. According to Christopher Adams, Tronical’s president and inventor of the Powertune, the self-tuning system can tune the strings to an accuracy of better than 2 cents, a very small difference in musical pitch. Twelve hundred cents make up an octave, the musical interval that corresponds to a 2:1 frequency ratio between two pitches. One hundred cents go into the interval between any black and white key on the piano. Most people can’t even notice pitch differences under 5 cents or so when two pitches are played sequentially.
Music aside, even a tone-deaf engineer can take something away from the Powertune’s electromechanical design, which overcomes both control and mechanical design challenges. Some of the control challenges relate to the physics of vibrating strings and fact that tension changes on one string tend to affect the other strings. Gibson CEO Henry Juszkiewicz calls automatic tuning a “surprisingly difficult multimode problem.” From a mechanical standpoint, Gibson wanted a tuning system compact enough to integrate into the Les Paul without changing its looks or sound. “The sound or appearance of the Les Paul is really the last thing you’d want to change,” says Adams.
Gibson has been billing the Robot Guitar as the “world’s first guitar with robotic technology.” Engineers might quibble that a few servos do not a robot make. And in fact, the Robot Guitar isn’t even the first to sport a self-tuning system. That honor goes to TransPerformance. Its founder, electrical engineer Neil Skinn, has been working on a patented self-tuning system since 1983. Jimmy Page of Led Zeppelin fame has been playing with such a system since 1990.
Scroll down for a photo gallery of Gibson's Robot Guitar!
Skinn’s Performer tuning system undeniably has more features than the Robot Guitar. It also takes a completely different approach to self-tuning than the Powertune system does. “The differences in how we each get the guitar in tune are subtle – unless you happen to be an engineer,” says Skinn. In short, TransPerformance uses an open-loop control method that relies on sophisticated calibration techniques. The PowerTune system, by contrast, relies on a fast, dynamic closed-loop approach.
You don’t have to be an engineer to notice some other key differences between the two systems. TransPerformance systems are customized for individual guitars and require extensive physical modifications to the guitar itself. That customization comes at a price – more than $3,000 for the Transperformance system without a guitar versus $2,499 for the entire Gibson Robot Guitar, Les Paul and all. “My customers tend to be the big boys of rock and roll, not your average Joes,” says Skinn, who also does a lot of business with session musicians and other less famous pros.
While it may not be the first out of the gate with a self-tuning system, Gibson could easily help bring it to the guitar-playing masses – as long as those players buy into the value of having an electromechanical system tune their axes for them. This buy-in isn’t a given yet. And there is no shortage of purists out there when it comes to a guitar as iconic as the Les Paul. “We’ve already gotten comments about what a stupid idea this is,” says Juszkiewicz. Critics of the system have tended to focus on the fact that tuning is both an easy and fundamental part of playing the guitar.
“In reality, tuning is a significant problem,” argues Juszkiewicz, an engineer by training and guitarist by avocation. And he estimates the “vast majority” of the worlds’ guitars are out of tune at any given moment.
Part of that problem is that even well-tuned guitars tend to drift out of tune when played, forcing guitarists to constantly fiddle with the tuning pegs. Juszkiewicz calls all these constant tuning adjustments “unnecessary overhead” that interrupts the flow of the music. “The guitar is a tool for making music and nothing about tuning is musical,” he says.
The use of non-standard tunings can further complicating the tuning process, especially during live performances. As Juszkiewicz points out, many guitarists use a variety of non-standard tunings, which can require the adjustment of anywhere from one to all six of the strings. Take Joni Mitchell, who has to be the undisputed Queen of Alternative Tunings. In a 1996 article in Acoustic Guitar Magazine, she reported using more than 50 different tunings over the course of her career.
From the guitarist’s standpoint, the Powertune system couldn’t be simpler. Just turn it on and strum. What many guitar pickers won’t ever know is that this strum sets a well-designed mechatronic system into motion.
The Powertune system essentially functions as a dynamic closed-loop control system. It measures the frequency of the strummed string, compares that frequency to the desired in-tune frequency and adjusts string tension to harmonize those two frequency values. It’s an iterative process that requires rapid cycles of measurement and adjustment. “We measure continuously when tuning,” says Adams.
To make these measurements and adjustments possible, Powertune relies on a collection of electromechanical subsystems in the guitar body and headstock. The system measures the frequency with a set of six piezoelectric transducers installed in the bridge – the part of the guitar that couples the strings to the guitar body. An 8-bit microprocessor installed in the guitar body compares the measured frequency with the desired “in-tune” frequency and sends the resulting control signal up to a second microprocessor, or “Neck CPU.” This second microprocessor sits on the back of the guitar’s headstock and controls the six brushless DC motors that individually adjust string tension. These tiny motors integrate into the worm-geared tuning heads, which typically have to work against string tensions ranging from 7 to 9 kg.
In a clever design twist that saves cost, weight and guitar modifications associated with wiring, the Powertune system uses the guitar strings themselves to send data and power up the neck to the tuners and CPU.
All that sounds straightforward, but the system in reality is a bit more complicated. Powertune’s tuning routines have to deal with the fact that tension changes to any string can affect the tension of the other strings. The system likewise has to deal with all the ways the physics of a vibrating string can affect frequency measurements. Adams cites one example in which different attacks on the strings can produce different sets of overtone frequencies. “You really have to know what you’re doing to make this work,” Adams says.
Adams declined to give any details about the workings of the tuning algorithms other than to say they do filter out any non-useful frequencies and also account for the decay of string vibration over time. “The speed and efficiency of the algorithms are what’s really critical for us,” he says.
Speed matters because Powertune’s iterative tuning process may require several measurement and adjustment cycles – all within the time afforded by a single strum – to reach the final tuning. “So the system has to be fast,” Adams says, noting that Powertune takes just 1/10-sec to gather and process the frequency information.
Adams adds that the efficiency of the algorithms allowed him to use a low-cost, low-power 8-bit microprocessor rather than a more expensive, more power-hungry component.
Aside from tuning, the Powertune system also has a mode that helps players intonate the guitar – essentially a string-length optimization that helps the guitar play in tune up and down the neck. Some guitarists intonate the guitar themselves, making adjustments to the bridge saddle locations until the fretted and harmonic notes at the 12th fret, the midpoint of the vibrating string, match for each string. Usually, though, a guitar tech does this kind of work. And Juszkiewicz points out many guitarists don’t bother to do it at all. With Powertune’s intonation mode, the system uses lights on its LED to guide the user through the process of making the necessary adjustments by turning screws on the bridge.
Making It Fit
As much attention as Powertune’s control architecture gets, the system’s mechanical design matters every bit as much. Juszkiewicz describes the Powertune installation as “non-invasive” in that it requires no permanent modifications to the guitar. And that’s one of the key things that attracted Gibson’s interest in the first place. “Our customers don’t want to dig holes in their axe,” Juszkiewicz says. “Even with the extra electronics on board, the Robot Guitar is one-hundred-percent Les Paul.”
To keep the Les Paul looking like a Les Paul, Powertune’s CPU and power supply all squeeze into existing pockets in the guitar body, those cut for the pickup and control electronics. Adams says this packaging coup was possible in part because he built the Powertune system around small, low-power components. The power supply, for example, consists of two AA NMH batteries.With a capacity of 2100 mAh, the batteries are good for about 300 tunings, Adams says.
The only visible parts of the system are subtle and removable if need be. Adams’ biggest mechanical design coup involves the tuners themselves. Although the self-tuning system's Powerhead tuners contain a 0.5-Nm brushless DC motor, a release mechanism for manual tuning and an 18:1 worm-drive to make the string tension adjustments, they still fit into the same space as a traditional high-end manual tuning head. And Adams notes that at just 46.5 grams, the Powerhead tuners are even about 2.5 grams lighter than their manual counterparts.
On the other end of the guitar, the Powertune system requires a push-pull master control knob. Yet even its presence has been minimized by having it do double duty as one of the guitar potentiometer control knobs. In the up position, this knob controls the Powertune; in the down position it handles the guitar pot. “There’s no extra knob to add to the guitar,” says Adams.
Gibson’s Robot Guitar debuted in a limited edition in December. And one of its first players is Juszkiewicz, who raves not just about the ease of tuning but the sound of a guitar that is essentially always in tune. “The chords just sound a little bit sweeter,” he says. “Once you try it, you’ll never go back.”
A History of Innovation
From a technology standpoint, Gibson's digital guitar and the MaGIC standard that enabled it may just represent the biggest leap forward since the company's famous 1957 Les Paul electric guitar. That year, two important technical innovations transformed that guitar. First, Gibson developed the "humbucking pickup," a patented design with opposing windings that decreased the effects of electromagnetic noise. And the company also introduced its "Tune-o-Matic bridge," a system that allowed adjustments in the length of the vibrating string to solve intonation problems. "We've come out with hundreds of Les Paul variations since then," says Walter Carter, Gibson Corp.'s historian. "But the fundamental technology hasn't changed all that much." And why should it? "The guitar is a rock and roll icon," says Carter. And he notes that, even after nearly a half century, guitar players still want this guitar's distinctive sound and shape. "It's our best selling guitar," he says. Long before rock and roll, however, Gibson had a long history of technical innovation. Here are some highlights:
1894. Company founder Orville Gibson adds a violin-like carved top to acoustic guitars, adding a powerful punch to the sound.
1919. Acoustic pioneer Lloyd Loar arrives at Gibson. He refines the construction of arched top guitars and mandolin-family instruments, including the addition of f-shaped sound holes. Some of his mandolins today sell for more than $80,000.
1921. The company patents the adjustable truss rod for stringed instrument necks.
1936. Though not first with the electric guitar—Rickenbacker had that distinction in 1932—Gibson introduces its ES150, a guitar that became famous in the hands of jazz great Charlie Christian. It features the single-pole P90 pickup that's still in use today.
1957. Gibson adds the humbucking pickup and adjustable bridge to its Les Paul electric, which had first appeared in 1952.
Gibson Guitar’s Newest CNC Machine Strikes A Productive Chord
Gibson Labs Sends Real-Time Audio over Ethernet