for you guitar heads out there...
Gibson’s Robot Guitar Tunes Itself
Joseph Ogando, Senior Editor -- Design News, January 10, 2008
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.
World’s First?
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.
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.
Mechatronic Tuning
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.
Here is a link with a video of it in action:
http://www.designnews.com/article/CA6519384.html?nid=2333&rid=1529234745