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A closer look at Don Gilmore's self-tuning piano system

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February 12, 2012

Kansas City mechanical engineer Don A Gilmore has developed a self-tuning piano system, wh...

Kansas City mechanical engineer Don A Gilmore has developed a self-tuning piano system, which uses an electric current to bring the instrument to tune in under a minute

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A few years ago Gibson began introducing some clever new technology to a select few guitars which automatically tuned the instrument and kept it there (seen most recently in the gorgeous Firebird X). I think that it's fair to say that robot tuning has not quite been a phenomenal success, perhaps due to the fact that tuning six strings only takes a few seconds and doesn't require any specialist training. That's certainly not true of the piano, which has more than 200 strings divided between 88 keys and its tuning is, for the most part, gratefully handed over to the experienced ear of a professional technician. In the 1990s, Kansas City mechanical engineer and classically-trained pianist Don A. Gilmore created a mechanical self-tuning device for the piano. From there he went on to develop a thermal system that can bring the whole instrument to tune within a minute.

Gilmore told us that when Dick Dolan of QRS Music was introduced to an early prototype of the self-tuning system in early 2002, he was so impressed that he immediately signed up the engineer to further develop the device - then consisting of a Basic Stamp program and sustained with the modified Ebow. The CEO was given a tuning wrench to "knock the string out of tune and it would go right back into tune."

"During my experimentation with the earlier mechanical device I had been using a modified Ebow to continuously sustain the string while I experimented with the wave on my scope," says Gilmore. "I had scratched through the potting on the Ebow to expose the legs of its amplifier chip, then soldered a wire to the appropriate leg and tapped the signal for my circuit. I had given some thought to a full, self-tuning piano, but it was never really practical until I had my epiphany."

The entire tuning process is said to take less than a minute and at the end of the playing...

"I was considering wild ideas about forcing electricity at a given frequency through the piano strings, wondering if it might have any effect on the pitch. I immediately went to my lab and hooked up a bench-top DC power supply to a string on an electric guitar that I had. I found that by turning the dial on the power supply I could easily control the pitch of the string. I also found that it took very little current or temperature change."

"Once I had started work on the self-tuner, it quickly dawned on me that this was an excellent way to do the automatic tuning (rather than have to strike each note over and over). This way I could tune all the strings simultaneously and have a steady wave that was easy to measure, and repeatable with each tuning."

On completion of the project, the self-tuning system was to head for the Prelude line of Story & Clark grand pianos. A change of management at QRS, however, and a subsequent change of company direction, meant that Gilmore's invention was never to emerge from its prototyping stage. After a few years of going nowhere, Gilmore opted to break free from QRS and develop the system independently.

"I am a mechanical engineer, so I had to learn electronics on my own and experiment and redesign the device over and over to get to where I am," he told Gizmag. "The device is all surface mount technology, so each iteration had to be sent to China to have the boards populated."

Each string of the piano has its own sustainer module, but this never actually touches any of the strings. Unlike the Ebow, which uses magnetic coils to pickup a signal, the self-tuning system makes use of infrared sensors as there would be too much magnetic interference and feedback between so many coils, so close together.

The low bass sustainer modules

"Each sensor has an LED infrared emitter and a phototransistor receiver," explains Gilmore. "Normally these sensors are used as a proximity switch, but I found that if I wire the phototransistor like an amplifier, I can actually see the vibration of the string's reflection in the signal."

To tune a string to the correct pitch, the note is entered into a continuous sustain and then compared with the frequency of one that's correctly-tuned (determined when the instrument if first warm-tuned by a technician at the factory) by an onboard processor. The pitch is adjusted using an electrical current delivered to each string via ordinary battery-compartment springs riveted to printed circuit boards positioned at the bottom of the tuning pins, where they are exposed to the underside of the pinblock. The current causes the strings to warm and expand, which decreases the string tension and lowers the pitch. Lowering the current cools the strings and raises the pitch.

"With some minor signal conditioning I can get a crisp square wave at the fundamental frequency of the string's vibration," says Gilmore. "I use a high-speed counter connected to a 100 MHz clock oscillator. I connect the string signal to the gate of the counter, so that each time the string vibrates it turns the counter on, then the next time it vibrates, it turns it back off, then I read the accumulated value of the counter. So I get a large, high-resolution number every time the string vibrates that represents the period of the vibration (which is just the reciprocal of the frequency or pitch). The system is so accurate that I can see natural fluctuations in the string's vibration. In fact, it is impractical to tune finer than about 1/10th of a musical cent because of this minute wandering of pitch."

"To handle the massive amount of I/O, I use an FPGA (Field Programmable Gate Array). This is just a big chip with a huge amount of logic gates inside. Rather than run on a sequential program like other processors, an FPGA can be permanently burnt with a custom logic circuit. So each string of the piano has its own dedicated logic counter and evaluator circuit that runs concurrently with the rest of the 200+ circuits. No polling, no delays. Just true, simultaneous and extremely fast operation."

The self-tuning piano system's main circuit board

"But even an FPGA only has so many pins and I don't have enough to also control all 200+ outputs. So I came up with a long line of shift registers in series into which I can shift a giant 219-bit word from a single serial line from the FPGA. Each of the bits of this word is connected to a small power transistor that turns 5 volts on or off for each string. By continuously changing this word I can control when and how often each string is turned off and on. So I can get 219 separate PWM (Pulse-Width Modulated) duty cycles and precisely control the pitch of all the strings simultaneously... and with a single wire."

The system raises or lowers the temperature of each string until the piano is in tune. When pitch is achieved, the continuous sustain ends and the system maintains the current to keep the string in tune. Gilmore says that the entire tuning process takes less than a minute, has a tuning accuracy of ± 0.001 cents and at the end of the playing session, the power is turned off and the piano returned to its previous state.

As for the cost of running the system, the current working prototype has a 1200-watt, 5-volt power supply that's said to draw about 800 watts or so, depending on the day's conditions. In the Midwest, energy costs about US$0.07 per kilowatt-hour, and as "it's only switched on when you play, that would mean a three-hour practice session would cost about 17 cents."

The current setup is designed for the system to be installed in new pianos at the factory, and initially tuned by a master technician. As such, the cost of the system could be absorbed into the overall price of an instrument (somewhat akin to adding options like air-conditioning to cars). Gilmore says that it might be possible to develop future systems that can be retrofitted into existing pianos but there are a few hurdles to overcome before that happens, such as finding a way to insulate the strings from the agraffes (guides at the tuning-pin end of the string) in the field.

Gilmore also told us that the system could also easily incorporate alternate tunings, as the stored factory tuning is just a block of 219 numbers at 32-bits each and so doesn't take up too much memory.

"The only added cost would really be the operator interface (a keypad and readout to be able to choose tunings)," he says. "I have also considered that it could potentially be a diagnostic tool for techs to plug into."

Installing the self-tuning system in the piano

At the moment, Gilmore is looking for manufacturing partners to take the concept further. The working prototype is demonstrated in the following video, in which Gilmore has connected a laptop via USB to the normally self-contained electronics in order to display some debug text and better illustrate how it works.

"I tuned a single note (three unison strings) so that it is easier to hear how far out-of-tune it is," he says. "I also drastically detuned the three strings to exaggerate. In reality, when the system is switched off the strings go sharp, but don't really sound too bad."

About the Author
Paul Ridden While Paul is loath to reveal his age, he will admit to cutting his IT teeth on a TRS-80 (although he won't say which version). An obsessive fascination with computer technology blossomed from hobby into career before the desire for sunnier climes saw him wave a fond farewell to his native Blighty in favor of Bordeaux, France. He's now a dedicated newshound pursuing the latest bleeding edge tech for Gizmag.   All articles by Paul Ridden
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11 Comments

So, it heats the string, lowering the pitch. This would tune a string that's been detuned sharp. But how does it tune a string that starts flat, as it seems is the more common out-of-tune condition?

Scott Detwiler
12th February, 2012 @ 08:13 pm PST

@Scott

I understand from the video the piano is factory tuned mechanically at a string temperature of 35 degrees C

In that case each string must be heated somewhat to be in tune. If a note sounds flat there is about 10 degrees temperature drop to environment temperature to correct it.

I love the technical detail in this article and the open inspired way the inventor shares his work.

Paul van Dinther
12th February, 2012 @ 09:16 pm PST

Considering he taught himself electronics, and then used an FPGA... Well done! Not a real fan of piano music but I'm sure it'll catch on somewhere. well done Don!

agulesin
13th February, 2012 @ 04:18 am PST

You are very talented, However, This is sort of not needed or not for any professional pianist who plays a Steinway etc. A piano is in tune to concert A, to a human ear not a computer as it will sound sort of out of tune. After the notes are in tune then the difficultly is the relative tuning 4ths 5ths and octaves. I have the Steinway video, and they very clearly state that their pianos are still the best (I agree) due to the fact that everything even tuning is done by hand, Yamaha uses computers and robots to aid in their completion. But still, well done, there is a market for it:)

Paul Perkins
13th February, 2012 @ 01:19 pm PST

The tuning you get with the self-tuner is a hand-tuning. A master technician tunes the piano by hand when it is warm and this tuning is "stored". No matter what the technician does with inharmonicity, harmonics, intervals, stretching, etc., the fundamental pitch of each string will be at a specific, repeatable frequency. The piano will return to that same tuning every time. If you don't like that tuning, it also has a retune feature. You simply flip a switch and the piano warms to a median temperature, have your favorite tech tune it perfectly, then flip the switch back and the new tuning is saved.

Don A. Gilmore

Kansas City

Don A. Gilmore
13th February, 2012 @ 04:06 pm PST

Awesome! A simple but brilliant way to keep a piano tuned, and I like the idea of storing your favourite tuning. Well done Don:)

Murdo
13th February, 2012 @ 07:57 pm PST

A wonderful invention, Mr. Gilmore!

I have a question that you have surely solved, and I am curious what the solution is. With repeated use of this system, it seems that all of the wooden parts of the piano would be subjected to substantial swings in relative humidity. Doesn't this cause the bridges, sound-board and pin-block to develop cracks? Wouldn't these changes in relative humidity also affect the regulation of the piano, especially in humid climates?

Also, what happens when the system is on and your cat jumps in the piano? :)

Jeremy Gould
15th February, 2012 @ 10:54 pm PST

The environment itself poses a much more severe hazard to your piano than the minuscule temperatures of this system. The keys in your pocket are hotter than these strings.

And as for your kitty, he will be happy to learn that only 5 volts are used to warm the strings, which cannot be felt to the touch.

Don A. Gilmore

Kansas City

Don A. Gilmore
16th February, 2012 @ 05:40 am PST

Sitar owners should love this.

Is the tuning unique to each piano ?

One would think that if each string were tuned to the desired frequency, a different piano tuned to the same set of string frequencies, would also be "in tune" but still sound different. This could allow portability of the tuning algorithm from one piano to another.

I may be missing something here. Different pianos would require different tension on each string to get the right frequency for each string. And different pianos would sound different with all the strings tuned to the same set of string frequencies, some better than others. Would there be a case where you want to untune or miss tune a piano to get it to sound proper, or at least the way you think it sounds the best ?

Instead of using the 'original professional tuning' as the gold standard for retuning could you use the mathematically perfect frequency for each string as the gold standard. Starting with all the strings tuned sharp it would take many iterations (thousands ?) to get all the strings in tune, but the processor is very fast. The response time for each string to adjust might slow tuning down some, say to five minutes ?, or even ten ? Would you have a good sound when done ?

Intellcity
16th February, 2012 @ 07:13 pm PST

You can have anything you want. Any tuning can be saved and repeated. That's really all it is: a tuning storage and retrieval system.

Don A. Gilmore
16th February, 2012 @ 09:00 pm PST

Wow... I'm kind of amazed Steingraeber hasn't offered you a position. This seems right up their R&D alley! In the video, it sounds like there's a pretty prominent beat in the unison, but perhaps that's the way it was originally tuned. Have you done any testing on how the heat fluctuations and transfer from string -> tuning pin -> pinblock affect its longevity or stability?

You're going to be famous! :)

djbf
25th June, 2012 @ 06:43 pm PDT
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