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HOWTO: Tune a piano the Keith Packard way

Recently, my colleague Dick Hamlet did an amazingly generous thing. He gave me a beautiful old upright piano. He was moving, and didn't want to move it, so I had it hauled to my house. How cool is that?

The piano needed some work, so Keith Packard and Carl Worth did another amazingly generous thing. They came over and helped me fix the piano. Then Keith tuned it. This in itself took several hours.

My Mom used to tune our piano when I was a kid. Since then, I'd never seen it done. So I thought maybe some of you would be interested in how Keith did it. It's quite repeatable, actually; all the way to easy. It just takes time, patience, quiet, and a bit of equipment...

DISCLAIMER: Why would you follow instructions by some idiot like me? I obviously have no idea what I'm talking about. When (not if) you break your piano, it's your own darn fault. When (not if) you hurt or kill yourself, don't cry to me about it. Piano strings are under tremendous tension; this makes them potentially lethal. Further, pianos are heavy; they can kill you just by falling on you. You have been warned.

Still here? First, purchase a tuning kit, available from any good piano store. The kit should contain a long-handled wrench for turning the tuning pegs, a bunch of felt and rubber tools for damping strings, and one or more tuning forks. Ignore the tuning forks; they're just misleading you.

Next, get Keithp's tone generator code, and compile it against fltk for your Linux laptop. This gives you a nice stable tone generator that can generate any note of the main octave, in a variety of tunings. Make sure you select "equal temperament", because that's how pianos are supposed to be tuned.

Now, take the piano apart until the strings are unobstructed by covers, dampers, etc. Do not mess with the hammers, felts, action, keys, etc. Anything that looks delicate is; you might do big damage.

Press the middle C key on the piano gently, and notice the hammer moving forward to strike the strings. It, like all notes in the main octave, will be aimed at a particular group of 3 strings. These 3 strings are supposed to be at the same frequency—multiple strings makes the note louder. Take the felt strip from your tuning kit, and press a fold of it into the gap just to the left of the group. The rubber tool from your tuning kit can be helpful for this. Then loop the felt strip up over the group, and push another fold of it into the gap to the right. Note that now only the middle string of the middle C group can vibrate. This is our goal. Keep moving to the right and pushing folds of felt into gaps between groups until you get to the C above middle C. Then stop. Now the central octave of the piano has only one note playing per string when a key is pressed.

Set the tone generator to play C, then put the wrench on the pin that tunes the middle string of middle C. Strike the middle C key, and listen for the difference between that and the tone generator. If the piano is badly out of tune, it will be obvious; this is unlikely. More likely, what you're listening for is "beats". A beat between two tones makes them sound like they're getting louder and softer. Maybe a few times a second, maybe ten or twenty times a second. Thrum-thrum-thrum. It's caused by interference between the tone generator and the string; it's hard to describe, but once you've heard it it's unmistakable. The goal is to tune the string to get rid of the beats.

Put ever so slight pressure on the end of the wrench handle. Probably you'll need to move it clockwise, to incrase the pitch of the string. As you start to tune the pin, you may feel the pin itself flex a bit, then the pin push back against the wrench as it moves. This is normal. At some point, the beat frequency should change slightly—the beats will start happening faster or slower. If they're faster, you're going the wrong way. If they're slower, you're going the right way. Relax the wrench and see how close you are. Repeat until the beats are gone. Now you've tuned one string on the piano. Repeat until you've tuned the center string on all 13 notes in the main octave.

Be sure to use small, gentle, minimal pin movements in tuning. Massive overtightening of a string might ruin the instrument. Failing that, the more tuning you do, the quicker the piano will drift out of tune. Minimal is best.

Once you've tuned the center strings of the main octave, you're done with the tone generator: set it aside. Now, pull out the leftmost fold in the felt strip you inserted earlier, which will let the left string of the middle C vibrate freely. Tune the left string to the center one by nulling out the beats, the same way you did with the center string and the tone generator. Pull out the next fold of felt, and tune the right string to match the other two. Now you've tuned one note, and are ready to tune the left string of C#.

When the main octave is tuned, move the felt strip up or down an octave, then beat tune each center string in the new octave to the string in the main octave. Continue in the obvious way until the whole new octave is in tune, then keep going.

The highest and lowest notes on the piano do not have 3 strings per note. For these, the rubber tool can be used to damp one of two notes to tune the other string in that group. When you're done tuning, put the piano back together and put the tuning kit somewhere safe for next time.

That's pretty much the story. Getting someone who's done it before to help you the first time you try is recommended. Have fun!

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Comments

Or you could tune the piano like my father did: breadboard the tone generators you need! I think he still has the circuit in the bench of his upright.

Ian

I had my piano professionally tuned after I broke it a bit ago. The piano tuner spent a long time explaining to me why his fancy electronic tuner was a way better option than tuning an octave to tone generators and working out. I'm not sure I entirely understood it, but I clearly need to do more investigating…

Once the center octave of the piano is tuned to accomedate the basic arithmatic error in the usual scales ie. "tempered" wich the tone generator can accomodate, one must then tune the other octaves to match. The problem with tuning these exactly to the temperment octave or to the pitches provided by the tone generator is an effect called inharmonicity. The stiffness of the string (which becomes larger in the tenor and bass strings wich are overwound with copper) makes the fundemental tone and its harmonics out of tune with eachother. An aural tuner (those who tune by ear) comprimises the octaves so that the intervals sound as pleasant as possible, and a modern PIANO electronic tuner (most of wich run about $1000 or more to buy) can measure the frequency of the string's fundimental and its harmonics and calculate the best comprimise (called a stretch curve) possible for each scale design. The small tuners designed for band and orchestral instruments do not do this. The comprimise involved in the design of pianos becomes more apearent the smaller the length of the strings, wich explans the usage of 7'-9' grand pianos in most concert halls.

Thanks much for a really nice comment and explanation! Clearly Keithp and I need to build the right FFT-based stretch tuner (B). In the meantime, though, probably the right thing to do is to build a tone generator that will generate the right mix of harmonics for the string being tuned, so that we can stretch tune by ear using the approach I describe above.

At this point, I've given up and paid a professional several times to tune and repair my piano. He's awesome, a world-class guy, and yet he's cheap enough I can afford to have this done once or twice a year.

Still, if I had a piano I couldn't afford to have tuned properly, I think I'd do what I could with our existing tone generator rather than just leave it in horrible mistune. It's amazing what even getting close can do for the sound of a neglected old beat-up upright like one sees all over the place.

You might consider the following arcane pieces of knowledge as further indication to keep your hands off this old piano you just got from a friend, or not.

If you are given a piano, chances are it is old. You might be given a piano that is badly out of tune. Both might indicate that you have been given one of those wooden frame uprights.

We had one at home - guess what, we got if for free as well Smile
It was rarely in tune, which drove my brother nuts who used it to practice for many years. If in tune, the sound is something special and I claim "unmistakable" (maybe because it is somewhat out of tune almost all the time).

We had it tuned regularly, that is every 4 or 5 years Smile
The tuner hardly ever dared set it to the right pitch, it was almost always about 1/2 note below standard (I know because it was next to impossible to have my French horn tuned to it). Why leave it off? Because when you tighten all 200 (or so) strings to gain the extra 1/2, the wooden frame might just collapse.

Also, the keithp method uses a "linear-out" approach. That only works when your frame does not give because of the added string tension - remember you have an OLD piano. You might have to do a few passes of the keithp method to get the entire instrument tuned.

PS:
We recently had to decide what to do when buying a piano. We spend just as much on a high-end electronic piano (Kawai CA 71) as we would have for a serviced and tuned used piano.
Why did we decide for an electronic piano? The killer feature in a house of 4 is: volume control! Smile

You make good points. One of the first things you need to do when purchasing (or inheriting) an old upright piano is make sure that it has a nice sturdy steel frame. You won't find hardly any pianos in the US that have wood or light steel any more—mostly because the weak ones have all busted (B). If yours has no or weak steel in it, I recommend just loosening the strings all the way and using it as a decoration; they're really delicate. Purchasing a piano is a whole 'nother topic…

I definitely have enjoyed my electronic pianos for many years. As you say, a good 88-key weighted touch sensitive model is not cheap. But having a volume control and never needing to tune are pretty big advantages.

I have to say, though, that the sound of my old upright, when properly tuned by a professional (B), is pretty special, and the touch is awesome. I grew up playing old uprights before there were any electronic pianos to speak of, so I'm probably just biased, but I really like having both.

It's like a fireplace mantle that you can install and remove. And no volume control needed if nobody plays it, ha.

I've tuned 4 different pianos badly with a square socket spanner (wrench) in the place of the classical tuner. I never thought about using felt to damp all except the inside string - but it's rather obvious, come to think of it, and a bit easier than putting your fingers in there for each note.

The socket plug on my socket set is just the right size to turn a piano key. The 1/8 inch socket, which is a star, happens to fit the wrong way onto the socket, giving a square socket spanner. This was a really cheap tool.

On one of the pianos I attacked, I had to jam in some paper into the thread of the peg holding the string to add enough tension to hold the string. On another, I jammed in some paper to move the entire damping mechanism towards the string by about 2mm - where it had previously been impossible to play, because the felt and glue on the dampers had shrunk ever so slightly, it came alive and sounds quite playable. My first piano needed to have some of the components serviced, having decayed over time - string came in handy.

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