Double String Open Unison Tuning Technique

Soon after I started tuning pianos, I started hearing about open unison tuning techniques. I was intrigued because it sounded like an advanced technique and I was interested in developing my tuning technique as much as possible. However, I could find nothing written on the subject at the time. I decided to learn how to do it on my own.

An open unison tuning technique is one where the tuner tunes all strings of the unison before moving on to the next note. The theory is that the unison must be tuned beatless for it to be used as a reference note for tuning future notes. Also, since the unison is tuned first and early in the sequence, there is more time to catch it, if it drifts.

Generally, tuning with a mute strip leaves most unisons until the end. Then if they are unstable, they will slip only after the tuner leaves, unless the tuner takes extra care to make sure they are stable.

One benefit of open unison tuning is that the tuner doesn’t have to make sure the unisons are stable, the technique demands that they must be beatless and stable, and if they slip, chances are, the tuner will catch it.

Single and Double String Open Unison Technique.

Single string open unison is when the tuner mutes two strings of a trichord, (or one string of a bichord), tunes the single string, adds a second string, and then tunes the third to make a beatless unison.

Double string open unison is when the tuner mutes only one string of a trichord, (with DSU you do not use a mute with bichords), and then tunes the double string unison (DSU) beatless, checks it to see which way it should move to be in tune, then detunes the DSU by moving one string in that direction, and follows with the second string to clean it up. The DSU is checked and moved this way until the tuner is happy with the result.

I can’t remember how I stumbled upon the DSU technique, perhaps I was intrigued by the challenge. I had heard of technicians tuning two strings at once and thought, “This is crazy. How is it possible?”. Anyway, I began to experiment with it and discovered how powerful a technique it is.

Once I started using DSU, I was amazed at how many benefits it had compared to the few benefits of single string open unison, In fact, there are so few benefits to single string unison, that it is no wonder to me why more people don’t use it.


Double String Unison BenefitsOpen String Unison Benefits
1. You can produce better unisons; they need to be dead on, to be used to tune other SBI's.1. You can produce better unisons; they need to be dead on, to be used to tune other SBI's.
2. You do not have to open the grand lid to insert the mute strip.2. You do not have to open the grand lid to insert the mute strip.
3. Better stability. You can catch drifting unisons easier.3. Better stability. You can catch drifting unisons easier.
4. There is no need to mute the piano before starting.4. There is no need to mute the piano before starting.
5. There is no pitch drift caused by inserting and removing mute strip.5. There is no pitch drift caused by inserting and removing mute strip.
6. Less wear on dampers. No mutes in bichords means no damper wear due to mutes being put in and out.
7. More improved feedback on stability. You can hear more precisely how hammer force affects the pitch of the string by comparing with its neighbour, during the tuning stroke and after you remove the hammer. Pitch change is easier to hear in unisons than in other intervals.
8. There is no pitch change due to adding unisons. The Weinreich Effect, if there is any, has already happened.
9. Unison shimming (see explanation below) is accurate to within 0.3 cents.
10. With DSU, it is much easier to tune birdcage or overdamper pianos.
11. No mutes are needed to tune the bichords.
12. You can use mutes with handles on a grand. Handled mutes tend to fall over when inserted into the tiny space between strings of a single note on a grand, but there is much more room between the strings of adjacent notes, and the handled mutes can be inserted far under the strings and the mutes are held much more tightly by the strings and the soundboard.
13. You can use Beat Matching (see explanation below) which can be a very fast way to tune octaves and other SBI's.
14. You don't need to put the Papps mute under the hammers in the treble section. This means you can tune some spinets without removing the board over the keys, or even the lid on some.
15. You don't even need Papp's mutes. Rubber mutes with handles work in treble.
16. It is much easier, and faster, to insert a mute between two adjacent notes, than to try and insert a rubber wedge mute into the tiny space between the strings of one note.
17. Almost no mutes ever fall into the action. The grip is stronger on mutes between notes than mutes between strings of one note; It is too hard to get the rubber mute deep enough between some strings so that it doesn't fall out.

This is not an easy technique to use. Its one con is that it takes time to master, but the rewards are great. Also, you can not “see the snake in the grass” as one technician puts it, referring to hearing beat speeds while tuning intervals directly; with DSU, you do not listen directly to intervals and change their size in realtime. You have to use RBI tests to determine which way to adjust the pitch of the DSU.

Learning DSU means you will have to get good at tuning clean unisons fast, and who doesn’t mind having that skill? After learning to tune a whole piano using DSU, your tunings will be more stable, your unisons will be cleaner, and believe it or not, your tunings will be faster.

Search this site for seminars, classes, or videos that demonstrate this technique. Search for “dsu” or “double string unison”, or just leave a comment or contact me.

It has been my experience that sometimes, technicians do not understand what I am talking about when I explain DSU. I am not listening to a beating DSU with another interval note. That would be impossible! How could anyone tune an octave, for example, when one of the octave notes is a beating unison?

The DSU method requires a clean beatless DSU to be played with the other interval note (a beatless trichord for example), then a judgement is made, then the DSU is moved by changing one string a tiny bit, using beat matching or shimming (see explanations below), then the other DSU string is changed to recreate the beatless DSU.

At no time during the beat matching or shimming of the DSU, is the other interval played. The only time you will know if you moved the DSU the right amount, is after you recreate a beatless DSU, and play it with the other interval note, and use the RBI tests.

SBI tests are more challenging because the DSU and trichords must be absolutely beatless. Any roll in the unison could easily be misheard as an error in the SBI size you are playing. But, SBI are also a great way to find unisons that need to be improved. When you find a SBI that should sound beatless according to your tests, but the SBI does not sound beatless, most of the time it is because one of the unisons are not beatless.

Shimming Unisons

This is where the pitch of a unison is changed by a very small amount by moving one string of a DSU until the unison just changes color, then moving the other string to recreate the beatless unison. In this way it is possible to effect as little as a 0.3 cent change in pitch.

Beat Matching

This is where the pitch of a unison is changed by an amount that is very close to the amount needed to create a beatless SBI like an octave for example.

Consider an out of tune A3A4, and you are tuning A3, trying to make a 4:2 A3A4.

1. Play A3A4 and listen to the 4:2 partial (A5)
2. Make a mental note of the speed of the beat at A5.
3. Now, detune the A3 DSU so that the 4th partial (A5) of the DSU matches the speed you heard in step 2.
4. Move the other string of the DSU until the DSU is beatless again.

In this way, you measure how far away the 4:2 partial of A3 is from a pure 4:2 octave and move A3 exactly that much.

It is techniques like beat matching, and others, that make DSU the fastest and most accurate tuning technique I have ever used.

Listen to me tune A3A4 using DSU.

13 Responses to “Double String Open Unison Tuning Technique”

  1. isaac says:

    Hi Mark

    I agree that the listening is better with open unisons.

    Then, manipulating so much the note is creating instability.

    I tune now unison as I go, because the result is more lively, but for instance yur initial octave could be tuned in seconds and directly just by listening to the octave quality.

    that is a very important process to master for the tuner to ‘recognize’ a good octave. (No tests really necessary, then, eventually ?3 10th that is all)

    after having used tests and see that they are always good you can forget them and use your ears, octaves are just some sort of unison,if you can hear the cleaning of partials you can tune directly “any type’ of octave. but what I think is that octave types are not necessary, what is is that the 4th and the 5th locate well in the initial octave.

    It may sound not technical, but once used to the good singing octave the tests show they are right, as the double octave, this is a huge advantage we just have to work for stability then as any modif create a reaction (hence the big advantage of knowing how sound a good simple, double, triple octave)

    I understand you use that as a teaching method, but in my opinion you hear yet your octave quality accurately.

    tuning with a strip mute, the Weinreich effect is balanced by tuning each external string a little high of the center one. This seem to work, assuming the pin setting is really good.
    But, the intervals have to be tested again when tuning unison if one want to be right

    Better congruence tuning unison as we go, but then we have yet all tools to recognize the octave, the others interval may agree and all of that can be done without testing by playing “unrelated” intervals

    Best Regards

  2. isaac says:

    the few persons I help for tuning I instruct them to “focus on the pin” more than on what they hear, (use earplugs to have less aggression and hear a more civil tone, and notify more easily the raise of power when the strings couple), for instance.

    I think it is important for them to obtain some understanding of the pin setting process before trying to obtain any kind of perfect interval

    As they are musicians most of them, it is up to them to know how a good octave is sounding or a good unison. I mean this is not the most difficult part of the process to them.

    if they have as a goal to make 6:3 octaves this will be soon very frustrating, even if basic checks are necessary, recognizing the “unison” in the octave is also a good learning method, for musicians IMO


    • Hi Isaac,

      So nice to hear from you. I don’t see you much in PW these days.

      I hear what you say about tuning octaves directly, but my recent study of that has inconclusive results. Subjects choose octaves all over the map, including wide 4:2/wide 6:3 and narrow 4:2/narrow 6:3.

      My hypothesis was the same as yours: a good octave, in fact, the ideal octave, which I thought existed, would be chosen 100% of the time when tuning directly, i.e. no checks.

      So now, I advocate using checks just to produce precise octaves. At least they will all be the same.

      Re:Weinreich. Do you know that Weinreich discovered that the final pitch will go down, or up, or remain unchanged when all the other strings are added in unison, and there is no way to predict?

      This is important because many techs who tune with high accuracy, realize Weinreich occurs but assume it is only in the down direction. To anticipate by tuning up a bit, means refinement will be needed if drift is not down. Also, the anticipated drop, if there is one, is a guess; more refinement needed.

      My focus recently has been on finding techniques that reduce unnecessary refinement caused by inaccurate settings. DSU makes the issue of Weinreich moot, since any settling, if it occurs at all, has already occurred before we use unison as a reference.

      Thanks for the reply. Could you comment so I know you received this and I can use this method to answer posters?


  3. isaac says:

    Hi Mark

    It is great that you agree that a “nice octave”, unison included or at last 2 strings each side (I think); will be “100 %” right when tuned directly.

    Then I like to have ideas on why, It may account on tuning experience, for that I dont really know but I learned that way and I can assure you that my octaves where not all shining, far from that!

    But I think we can develop a feel for congruence, or just we are sensitive to the amount of rise of power when the octave match, the better tone projection…

    I do not think that I will say it is “more precise” than matching partials, but if it sound good to us and it allows tuning within the rules is it so important ?

    What I think is that starters need to learn to listen, but to do so they need to manipulate the lever really slowly enough so they can hear the different partial matches occuring, the beats appearing, with ample time to decide when to stop the pressure on the lever.

    For that at some point they need to take full control on the sounding lenght, then full control on the pin

    All of a program, but I think starters may understand the pin in priority

    as long as the note is played enough listening is less absorbing

    if not you stay for hours listening to a very small portion of tone which is often not really useful for the pin or the final pitch obtained

    Of course double open string is not a problem for doing so, but I think the starter have to understand the hole wher ethe pin moves is slippery only in one direction, the other direction the pin tend to brake, in fact if the pinblock is good it should brake without any help

    That mean the wood in the hole is oriented , when we turn the pin we keep that orientation
    Turn clockwise and you rub on the useful part of the hole, then pin setting lower and I think the block may suffer in time

    It brake because the wire is on one side of the pin, if it was in a hole in the middle of the pin, pin setting would not be possible;

    So I consider we only tune “up” (on return, if necessary it is better to lighten the pressure on the bed of the pin, less in uprights but on grands if too much I take the lever in left hand)

    ALl the best


  4. isaac says:

    about Weinreich, yes I know his findings, but find he do not describe accurately enough how he did obtain them

    I just think that parameters as wrong coupling or (more probable) not tight enough pin setting, may have make the results more erratic than they should;

    A lowering seem easier to explain or theorize ; a rise less;

    anyway with strip muting and building the unison “up” this seem to correct the lowering, be it because of weinreich effect or the soundboard and bridge motions.

    It is then a little difficult to tune with direct unisons without evaluating some slippage of the pitch during tuning, so we are always in our anticipation and building the pitch “up”

    I am not far to believe than the usual 4:2 6:3 octave is also envisaged because of future drift, and is also a little enlarged to help with tempering the 5ths and the intervals up of the temperament (a larger initial octave “cover” mistakes more easily than a very “flat” one, henc ethe difficulty of making a Japanese type tuning when one is used to enlarge the initial octave,

    Best regards


  5. isaac says:

    Y have seen your study

    comments; On one string, only tuners can have an idea of the octave, and I think that happen when we are in front of the piano not on recordings

    You may have used at last 2 strings by note to provide a better appreciation of the coupling

    The piano quality, iH is very high it does not help, as you know, to hear clearly pitches, as the pitch change during sustain with the lowering of the partial strength (the mix change in time)

    That may explain the inconclusive results partly, and for the last part certainly the systems used for reproduction may have a role, I for one did not use headphones as I believe I can recognize “my” octave even on one string on a poor system; But this was inconclusive too even if I had a preferred octave in the end ; the A A was acceptable the F F none was to my liking (that last point probably due to the absence of unison)


    • Agreed.

      I am working on a new test using recorded piano strings and users “tune”A3. The app alters the strings’ frequency by 0.5 cents, roughly the desired precision for ET. This allows better resolution and more options than the early test. Thanks for comments.

  6. isaac says:

    that sound as a good idea
    will it be possible to add a string for more volume ?

    I believe that our good octave is perceived as much in the body than the ears, and possibly will depend on the room accoustics a little, (I mean, when directly tuned without checks)

    Good day

  7. Isaac OLEG says:


    Back to some update

    Actually , besides the fact that I can tune unison with different methods, on a well responding piano (not too much parasites or false strings) , the nicest result is obtained by tuning the whole unison open

    I think this can be obtained after having understood how to tune with doubelts, hence how to deal with the “opening”, of the tone to obtain attack and good projection at the same time

    When adding the 3d string one stay focused on those pârameters and there is no problem, the only exeption is when wanting “viennese style ” where the 2 doublets balance each other (raising then raising again the sme) which reinforce the tone of the attack; this is harder to obtain with 3 strings sounding


  8. Edward says:

    The whole “Double String Open Unison Tuning” thing seems like a solution in search of a problem. I’m all for innovation, but what problem is this fixing? Pianos have been tuned one string at a time for centuries. I’d like to see some kind of evidence that DSOUT will hold a tune better/longer than traditional technique, if that indeed is the whole point.

    • Hi Edward,

      Thanks for the comment. With all due respect, DSU is a brand of Open Unison tuning and Open Unison tuning is generally accepted to be a superior method to produce better unisons by many professional technicians. True, not all, but the fact that so many adhere to it and expound its benefits doesn’t seem to indicate “a solution in search of a problem”.

      As far as evidence, I have listed many pros for open unison tuning (and many more for DSU) and a little research on your part should help convince you of that. For example, search Professor Gabriel Weinreich Unisons, you will find, after some searching, this paper:

      Many of the other points made should be obvious.

      What is also common and frankly disturbing, are the number of technicians who, while having no experience with high level accuracy tuning, choose to judge a technician who has a strong physics background and uses that to prove and disprove their own hypotheses, without doing any research.

      No one is saying you have to tune this way. No one is saying you would even get better results than you get now, certainly not right away. But in the same breath, no body should be saying that a method like this that does have some scientific support like that of Professor Weinreich, should be identified as a “solution in search of a problem. I’m speechless.

    • Olek says:

      Edward, and Marc hello, and best wishes for new year

      There is a flaw in the answer from Edward (unless I do not understand him) .
      Pianos always have been tuned 2 or 3 strings at the time, not one. One for pitch reference, relative to other yet tuned notes, then another, where the weinreich effect play a big role, and then only the tuner have the choice for the 3d string. (open double first unison or all 3 strings sounding)


      • Isaac! So nice to hear from you.

        I think what Edward is referring to is using a mute strip to tune the first string. Then the others are added as the strip is removed. Mute strip tuners usually never check if the first string tuned has drifted. Their belief, as was mine, is “once tuned, always tuned” and the idea of rechecking is not considered.

        When I was younger, I avoided that kind of accuracy because it would have quadrupled my tuning time. LOL.

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