Organistrum: its tuning and keyboard

Organistrum: its tuning and keyboard



The aim of the present article is to present the ultimate result of my research on the possibility of rebuilding the Organistrum (Giuseppe Antonio Severini, Organistrum. A case of experimental archaeology. Tipheret, 2020)

1.Sources and features

The information we have on the instrument comes from a dozen images in books and works of art of the 12th century.

Constant elements

  1. The Organistrum has an « 8 » shape, with a rectangular extension.
  2. The dimensions are such as to occupy the knees of two men seated side by side.
  3. The wheel and the crank are a characteristic element, as are the three strings, in one case two, in one other perhaps one.
  4. The row of keys ends within the middle of the string.

Variable elements


  1. The number of keys can change: 6 to 11 (or 12).


Unknown elements

 I. There is no information about the tuning and the musical scale but from a plate in Martin Gerbert, De cantu et musica sacra, 1774. The same drawing gives an idea of the possible mechanism of the keys.

II. We know nothing more about the inner structure of the keyboard.


From these premises it follows that the replicas of the Organistrum so far attempted are at least partly hypothetical.

This obviously concerns the Variable elements  and the Unknown Elements.

Almost all the replicas take as a model the Organistrum of the Portico de la Gloria of Santiago de Compostela because, compared to all the other representations it is the richest in details, it has the maximum number of keys, it occupies the most important location.


There are 12 keys within the octave, the first of which should be the nut : they are definetly too many, unless you want to conclude that this is a chromatic keyboard.

Another arbitrary element lies in the choice of the generally adopted fifth and octave tuning, inspired by the organum parallelum polyphonic technique, described in texts that precede any known depiction of the Organistrum by at least a century or two. Instruments made following these hypotheses have little use in the performance of medieval music.


2. A different solution

In search of a different solution, I found myself reconsidering two objects that are certainly of the first level.


A.) The only drawing of the keyboard that we have left, complete with indications on the scale and on the structure of the keys, is the one copied by Martin Gerbert from a 12th c. manuscript, now lost, in Saint Blaise monastery.

Gerbert's keys have been interpreted as revolving bars with a long "spatula" tangent placed under the strings. The tangent would be brought into contact with all three strings simultaneously through a rotation. This system does not work in practice.

I prefer another interpretation of this drawing: the eight keys would be rotatable or lever acting from above the strings, pressing them against fixed frets, and it works.

Gerbert provides a scale for the instrument: from C to the next C with a single accidental, Bb. The fact that the intonations of the other two strings are not indicated leads to the conclusion that :

  1. they all had the same frequency;
  2. were in C with different octaves;
  3. Gerbert has forgotten to copy them.

The indicated scale is the canonical one and logically must be respected. The indication for the tuning being incomplete, this does not mean that it should be overridden. It is preferable to stick to hypotheses 1. and 2.

So we are faced with a diatonic instrument capable of producing all the intervals of the diatonic scale with a continuous sound. As several authors have observed, it seems to be an evolution of the Monochord. What could this instrument be used for? To provide a certain reference of the notes (a tuner), to play pedals in polyphony helping the singers in intonation.


B.) The musical repertoire coeval with the representations of the Organistrum, all of the 12th century, gives us more suggestions.

The manuscripts of Limoges, Winchester, Santiago de Compostela and Paris (Notre Dame), show an interesting two parts polyphonic repertoire. The scales are strictly diatonic. The only alteration used is Bb. These compositions were sung and intended for the liturgy. Many of these, called organum floridum or melismaticum, consisted of a bass vox principalis, and a higher vox organalis. Each note of the vox principalis corresponds to groups of many notes of the vox organalis. The extension of the vox principalis in the Magnus Liber organi of Notre Dame is mostly from C3 to D4, rarely up to F4. The compositions in the F key start at A2 and jump to C3, never requiring B and Bb in the first octave.

It is possible that the Organistrum as described by Gerbert effectively entered into the performance of these parts.


3.More than eight keys.

How should we consider keyboards with more than eight keys?

They are actually only two:

  • organistrum from Collegiata de Toro (Spain) : the nut + 9 keys ;
  • the one from Santiago de Compostela : the nut + 11 keys.

I think the most realistic keyboard is that of Toro, which only adds one tone (D) to the octave.

In the case of Compostela it is very difficult to think of an extension of the diatonic keyboard by two tones and a semitone without visibly exceeding half of the diapason. The Santiago instrument, certainly the most beautiful, has preponderant symbolic value, as amply shown in my book. The 12 keys do not want to indicate the intervals of the scale of the instrument, but those of the cosmic harmony according to Pliny, as can be seen listed next to many grids of planetary latitudes in 11th and 12th century manuscripts of astronomical content. The setting of the instrument at the center and at the top of the Portico describing the Glory of Heaven, the decorative details and the fundamental measures of the instrument have an evident astronomical and theological inspiration. Finally, the sculpture belongs to a masterpiece of the highest level, as one of the three most important sanctuaries of Christianity deserved.



4.Acoustic results

As with all theories, a crucial aspect lies in the experimental verification.

I have listened to many instruments, others I have heard in recordings, I built four different types myself. My conclusion is that the most coherent and most convincing version, with the most pleasant sound, is the one with the three strings in C3, C3, C2 and a diatonic fingerboard with levers acting over the strings.

ORGANISTRUM.  The book  2020

ORGANISTRUM. The book 2020

The Organistrum is depicted in a dozen works of art of the 12th century, it is rarely mentioned in contemporary written sources and disappears at the beginning of the 13th century. Despite the brevity of its life, this instrument boasts a prominent role within the medieval Organology. This is due to both the originality and ingenuity of its construction, and its prominent position among the sculptures of the famous Portico de la Gloria of Santiago de Compostela cathedral, one of the three most important shrines of Christianity. 

Since musicologists and organology experts dedicated little attention to the Organistrum, we luthiers were to perform the historical survey, though not necessarily equipped with the specialized knowledge necessary. Some of our ideas, mainly those concerning the tuning and the structure of the keyboard, might therefore be rather arbitrary or insufficiently grounded. The negative evaluation given by the specialists of medieval music only adds points to the concerns. In the performances of the last thirty years, the presence of the Organistrum is, as a matter of fact, absolutely marginal. Just consider the discography - were it not mentioned in the sleeve notes, it would be difficult to even notice the instrument’s presence. Its function is mostly reduced to the performance of drones, barely audible at the beginning and end of the rare pieces in which it is used. In live performance, the instrument is often exhibited in the center of the stage as an unusual object, one definitely bizarre: we know how this category of the bizarre is inherent to our vision of the Middle Ages. Even in this case, the acoustic presence of the Organistrum remains unsatisfactory, especially when it is inserted in rather improbable medieval “big orchestras".

Moreover, musicians within the folk / rock scene have used the instrument occasionally, amplifying and distorting its sound, adding no merit to it.

To conclude, the field ultimately came to produce an instrument as showy as it is devoid of musical value: one destined for museum windows rather than concerts.

Such an inglorious outcome can be explained in two ways: either the Organistrum should really be considered an almost ornamental object, or its reconstruction is at least in some points flawed.

To solve these doubts and define the entirety of the issue, it was necessary to undertake a new phase of research, geared towards understanding the actual historical physiognomy of the instrument. 

In the first phase of my study, I carried out research pertaining to an ordinary study of Organology. Failing to solve many of the problems that were arising, I conducted further investigation in new directions.  

The language of symbols emerges from a deep substratum of culture which, through art, reveals the presence of archetypal forms of very ancient origin.

The studies of Jurgis Baltrusaitis, for example, have demonstrated how many elements of medieval European architecture and decoration come both from the Roman world and, through the trade of manuscripts, pottery, jewelry, fabrics, from the Middle East and from even more distant areas, such as Persia, India, and China. From his studies, it emerges that the cultural heritage of peoples is equally composed by images and concepts that have very ancient roots and testify to an ancestral circulation of ideas and experiences dating back to even (occasionally) prehistoric times.

The Organistrum probably never quite made it past particular social and cultural contexts (that of religious communities, monastic or urban, on the way of pilgrimage or inside the cathedral schools), and continued to be used, together with the Giga, for only barely over a century.

Within this context, it had to play a particular function and took on a symbolic value in its representations. It is therefore essential to broaden the investigation beyond purely technical and structural elements. We must turn to the ideology, theology and spirituality that lively characterized its fermenting cultural environment. 

I have identified three main sources of reference: the Christian exegesis of the Bible, the school of Latin Platonism and the Jewish Kabbalah.

To buy the book (Italian ): 

Replica of Compostela Organistrum  by Giuseppe Severini

ORGANISTRUM. The "magic word" in M.Gerbert's drawing

ORGANISTRUM. The "magic word" in M.Gerbert's drawing

This famous image comes from Gerbert's pubblication entitled: De cantu et musica sacra, written in the 18th century.

The author copied a drawing from a 13th century manuscript, now lost. It is considered the most important written source regarding the instrument called Organistrum : it shows clearly its general shape, the number of strings, the presence of  a cranck and a wheel, the keyboard and the musical scale.


Unfortunately, the information about the tuning is incomplete: only one string out of two is indicated: c.

May be the author judged this indication was enough (intelligenti pauca), so, we could consider two solutions:

- all three strings tuned in c,

- one in c and the other two "in harmony ", i.e. c, g, c'


Since the keys seem to operate the three strings at a time, we would be able to play a whole c-c' diatonic scale in the first case and a sequence of parallel fifths and octaves in the second one.


The last pattern has seduced many luthiers and musicians in the last decades, cheated by the erroneous attribution to Odo de Cluny (10th century) of  a manuscript entitled "Quomodo organistrum construatur".Their idea was that the Organistrum  - certainly devoted to sacred music - could have been related to the contemporary polyphonic technique called Organum parallelum

But the famous text, once considered the earliest source for the studies about this instrument, has been recently recognised as a 13 th c. work by anonymous author.


Since the story of the instrument has been relocated in the right period,  the 11th and 12th century,  we observe that the musical scene looks rather different. Many anonimous composers were developping much more sophisticated and interesting polyphonic techniques: discantus, organum duplum  and organum melismaticum or floridum , organum parallelum  being no longer attested.


A new reason was then adduced by some authors to justify a parallel fifth and octave tuning: the misleading interpretation of the letters written around the instrument wheel in Gerbert's drawing: m a G/ a D a.

These letters could allude to one or more tuning patterns of the instrument: a D a, or d D a.

But it is rather difficult to explain the first part: m a G. Eventually,  all  interpretations based on such letters cannot match with a C scale.


In fact, the letters compose the word magada  that  means bridge. This word was used frequently in latin 11th and 12th century music treatises, to indicate the bridges of the Monochord. It comes from Ptolemeus Harmonikai  and was transmitted  by Boetius in De institutione musica, lib.IV, chapter 18, in his description of the monochord: "duo semisperia, quas magadas greci vocant". Thus, the monochord bridges were half spheres, as stated by Ptolemeus, in order to touch the string in one point only.


It is interesting to point out that 11th c. treatise entitled  Divisiones monocordi, inc. Studiosis necdum in musica provectis hec de monocordo...

M 17 sup (Biblioteca Ambrosiana, Milan ) still reports the name magada to indicate the monochord bridges, while this word is changed into rotulum in 13th c. manuscript  Quomodo organistrum construatur, in which the word rotulum  logically indicates  the semispherical bridge and not a wheel (rota).


As a matter of fact all these texts and others called Mensura organistri  are concerned with the description of the pythagorean diatonic C scale

and the method used to draw it by ruler and compass following simple ratios and they never describe any musical instrument but the monochord.


I would like to quote some lines from Francis W.Galpin, Old english instruments of music. 1910 (old books are not always the worse ones !):

"The Organistrum, for such was its name at first, is undoubtedly derived from the Monochord, a simple contrivance for ascertaining the intervals of the musical scale by a series of movable bridges".


In medieval Europe the C diatonic scale had an outstanding theorical value both because it offers the essential pattern of the Pythagorean system and because it contains the basic natural exachord of Guido d'Arezzo, but in sacred music practice the more frequently used modes were protus autenticus (D) and plagalis (A), protus autenticus  offering also the musical scale  generally associated to musica mundana or music of the spheres.


Then, even if I would love to say that the wheel instruments were invented to make the continuous "circular" sound of the heavens audible, I definitely can't.

First of all the scale is not the planetary one, secondly the presence of b betrays a practical concern, and finally, you cannot hear all the  sounds together.


So, I guess that, with all strings tuned in C, the Organistrum could have been useful in backing the tenor part in compositions called Organum melismaticum, like the Romanesque pull-organ, and unlike later noisy "country-folk"  instruments.


Musical examples:


The book (2020): 


































The idea of a polyphonic keyboard on wheel instruments derives from my studies about 12th century Organistrum.



The three strings are tuned to the same pitch (C),  eight tangents being distributed among them: two on the first string, three on the middle one and  three on the third.

Thus it is possible to play  not only a melody  accompanied by  drones, but  some double stops (fourths and thirds) too.


I introduce you SONYA, the polyphonic symphonia.






Diapason: cm. 43