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.

Please read my article on-line:

see also:  Giuseppe Antonio Severini, Organistrum. Un caso di archeologia sperimentale. Tipheret, 2020. Italian text only.


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

 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 B2 and Bb2.

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.


Plinian Harmonia besides Planetary latitudes graph from Trinity College Cambridge, ms R15.32, p.6

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. It's important to underline that this sculpture, belonging to a masterpiece of the highest level, as one of the three most important sanctuaries of Christianity, deserved great symbolic significance.


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 and a diatonic fingerboard with levers acting over the strings.


Watch this video:


Best source:





ORGANISTRUM. A short study about its possible repertoire.

ORGANISTRUM. A short study about its possible repertoire.

The Organistrum is always depicted in instrumental groups either related to the parade of King David (Old Testament) or to the group of the 24 elders of the Apocalypse (New Testament). The characters are in full robes, except for one of the two musicians from the Hunterian psalter (the one in charge of the crank, may be a servant). In the latter representation, in the capital of Boscherville and in the sculpture of Compostela, the musician who acts on the keys seems to have his mouth ajar, as if mid-song.

It is necessary to carefully analyze the few documents at our disposal in order to obtain as much information as possible.

Before I introduce this new phase of my research, however, let us recall the thoughts of two authors who had the same intuition about the function of Organistrum.

Francis W. Galpin in Old english instruments of music, 1910, states:  

"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".

Laura de Castellet in: The sound space: Thought, Music and Liturgy, in the volume: Spaces of Knowledge: Four Dimensions of Medieval Thought, Barcelona, ​​2014, writes:

“At any rate, the Organistrum was not conceived as a relative or a surrogate of the organ for the embellishment of sound within the temple. For instance, the presence of an organistrum amidst the twentyfour elders of the Apocalypse of the Gate of Glory … and at the collegiate church at Toro (Zamora), does not mean that such instrument leads any kind of concert, but that it symbolically represents the study of the language of sound, mathematical speculation, and cosmological order, and the approach to the divine essence. The elders are not making music, but rather preparing themselves - some of them are tuning their instruments- both intellectually and spiritually to face the advent of a new order of things. » p.39.  

According to both scholars, the Organistrum finds its origins from an instrument used to measure the pitch of sounds since ancient times.

However, in order to seriously consider the possibility that it played a significant role in musical practice too, it is necessary to identify its possible scope of use.




The context in which the instrument is described or depicted is always, and only, that of sacred music.

When it was still believed that the Organistrum had first appeared in the 9th century, it seemed to some to find an indirect reference within the treatise Musica enchiriadis.

The anonymous author meticulously describes a polyphonic practice called Organum parallelum. He states that the use of instruments was allowed in polyphony, so long as these strictly respected the voice pitches (Pia,2011). This encouraged some researchers to attribute to the Organistrum the role of Organum parallelum performer. They stated that two strings were tuned an octave apart and the third had to be tuned to the fourth or fifth (e.g. C3 – F3 /G3 – C4) (Rault, 1985). In other instruments one string is tuned to a fundamental pitch, the other two a fifth above (Kurt Reichmann). When operating a key all three strings are shortened.

Today, we know that the documents, correctly dated, place the lifetime of the Organistrum between the end of 11th and the end of 12th century. In this period, musicians were experiencing new forms of polyphony as the organum sillabicum (es. Ad organum faciendum, M.17sup., Bibl.Ambrosiana, Milan), organum melismaticum or floridum (codex of Saint Martial de Limoges and Magnus liber organi de Notre Dame), the discantus, the clausula and conductus (Codex Calixtinus and Magnus liber organi de Notre Dame).

It is impossible not to wonder whether the Organistrum had any relationship with such repertoires. If it did, we must then direct our attention to finding out how, with what tuning and using what type of scale.

The first element of judgment is the definition of the area of ​​sacred music as characteristic of all representations of the instrument.

The second is the diatonic scale indicated in the precious drawing by Gerbert.

The sacred music of the time theorizes and exclusively employs the diatonic scale - this must have been the scale of any musical instrument. The series of bells and keyboards of the Romanesque organs do not, in fact, include fictae other than the Bb.

The keyboard of the Compostela instrument, with eleven keys within the half of the diapason, and therefore apparently chromatic, could probably be organized as in fig.9.


                    A2      ---          B         C3               D                E          F                   G 


A3     ---       Bb        B        C4                  D                 E       F                 G4


                      A2       ---        B         C3               D                E          F                   G                    


0                    1        2         3*         4        5        6       7      8*       9      10        11  



fig.9  Diatonic  keyboard with 11 keys within the half of the diapason.


The nuts of the bass strings, both tuned in A2, are positioned further forward the nut of the middle string, tuned in A3, by the space of a semitone. The keys have hurdy-gurdy-like separate tangents and have vertical movement. Keys 4, 6, 9, 11 touch only the outer strings to play the notes of the lower octave. Key 1 acts on the central treble string passing under the nuts of the lateral strings. Keys 2, 3, 5, 7, 8 and 10 touch the treble string to play the notes of the highest octave. Keys 3 and 8 are the only ones enabled to act alternatively on the central string or on the side ones, after 90° rotation of the bar (fig.10).

The scale starts from A2, and not from C3 as in Gerbert, because A2 is the lowest note of the repertoire (cod. Pluteus, c.LXX r.), as can be seen from the analysis of the parts of tenor of the melismatic Organa in Magnus Liber Organi de Notre Dame. The tenor part’s highest note is generally D4, and only in very rare cases F4 (code Pluteus, c.LXVII r. And LXXXIIII, r./v.), while A4 appears only in non-melismatic compositions (code Pluteus, LXXXVIII r.).

In the first octave the Bb is missing, though this note is not foreseen in the Guidonian Gamut and consequently is not used in this repertoire. The natural B of the same octave is found, at least to my knowledge, only in one case (cod. Pluteus, c. CXXII).

To play the notes of the first octave, the player who turns the crank keeps the middle string away from the edge of the wheel. To continue on to the second octave, he moves the side strings away. All this to avoid using the Organistrum as a drone instrument, limited to only two modes at a time, in a style appropriate for secular and folk music performances.

Using the same string selection system, the compass from A2 to F4 - and up to A4 - can also be obtained with the 8 key diatonic keyboard, having the foresight to tune two strings in A2 and the third one an octave higher.  (In this case, however, the position of the sib would necessarily be at the beginning of the row and not, as in Gerbert's keyboard, at the end).

Should this system look too complicate we can imagine a shorter diatonic keyboard for Compostela Organistrum (long enough for playing most of the tenor parts of the repertoire) starting at A2 (all three strings), with no Bb in the first octave, reaching the eleventh key on D4 including Bb in the second octave. In this case the keys row would end visibly beyond the middle of the string (1/2 + 1/8 of diapason), the spacing of the keys couldn’t be regular as in the sculpture.

Nevertheless, no matter how structured, the diatonic keyboard of an Organistrum or a Romanesque organ could have been useful to the musician in order to check the right intervals while composing the vox organalis of organum melismaticum.

 (translated from Italian)

from the book:

Giuseppe Severini

"Organistrum. Un caso di archeologia sperimentale"
Watch the video:  
Read more in English:


Organistrum keyboard  from Portico de la Gloria, Santiago de Compostela.

Organistrum keyboard from Portico de la Gloria, Santiago de Compostela.

Symphonia / Organistrum


in Santiago de Compostela cathedral.

(Inquiry into a troubling problem of interpretation.

Analysis of possible solutions.)


In former articles, I both wrote about different aspects of this problem and discussed practical means to build an acceptable replica of the instrument. My aim is to deal not only with organological and technical subjects but to examine musical ideas connected to them, the way Music was considered both as an art and as part of the mathematical knowledge of Nature, since Pythagoras to the Middle Ages and further.


Several researchers have already carefully studied the few witnesses related to this instrument. I am not going to repeat the whole list, I just want to offer a short survey here.

We can find many features common to all specimens: the soundbox, consisting, as usual, of two oval/circular parts plus the neck, three strings are stretched along this body, then a keyboard showing 6 to 8 keys within the half of the diapason, sound holes are often in a D shape. The keyboard mechanism is depicted only once, in an 18th-century copy (Gerbert) of a 13th c. deperditum  manuscript: 8 revolving keys and the list of the notes, from C to c (including Bb and B) are clearly visible.  This drawing tells us clearly that one of the strings, (maybe all the three strings) was in C and that the three strings were touched by each key at the same time following a diatonic scale.

The six letters on the right compose the word magada (latin but having greek origins) written at the right place, around the wheel and the bridge. (In musical treatises, i.e. the manuscript containing the most famous Ad organum faciendum in Biblioteca Ambrosiana, Milan, XI c., magada is the name given to the bridges of the monochord)


Another well known 13th-century manuscript entitled “Quomodo organistrum construatur” illustrates the method to divide the monochord into the eight stops of a diatonic scale starting from Ut, but we don't find a description of the instrument nor information about its use. Scholars guess it was played mainly for sacred music along the 12th century. Christopher Page, the only one who faced the problem of the name: Symhonia / Organistrum, has several doubts about and no definite answers.


We know that almost all depictions and witnesses belong to the 12th century, but the year and the decade are mainly unknown. Since it is impossible to follow an exact chronology we cannot pretend to outline the evolution of this instrument. To study carefully the observable features is the only serious way to face the subject.

In Ahedo de  Butron (Burgos) sculpture, one of the musicians might be turning a crank with his right hand, while with his left-hand forefinger he is actually touching the second string of five; the second musician is touching the third string with his right-hand forefinger and with the other hand is turning the corresponding tuning peg. 


Hortus deliciarum


There is no evidence of a keyboard  in Hortus deliciarum manuscript. In Ahedo, since there is no trace of both crank and wheel, possibly the two musicians are either just tuning a long size Viella or tuning an Organistrum with no keyboard:

Soria Ahedo de Butron

In Soria sculpture (Spain) we observe only one string (?), no bridge, no wheel, no keys. The musicians look as they were actually turning a wheel and pulling the keys, but the damages suffered by this sculpture do preclude a clear observation of details. On the contrary, the similarly shaped instrument in Boscherville capital (France) presents crank, tailpiece, wheel, and keys.

Bosh Boscherville

What was this wheel intended to do, but to produce a continuous sound? This is the first observation with musical relevance in our description. Now, suppose we have built a long size Viella, about twice the size of a usual one, with a wheel in it: one of the two musicians can stop the strings all along the neck with his fingers, but he is not at ease cause his fingers interfere accidentally with the other strings. This is why a system of keys might have been suggested. In some depictions they appear, 6 to 8 within half of the diapason. They look like flat bars passing beneath the strings (Boscherville and Vercelli) or we can see the top of them protruding from the lid that hides the inner mechanism. That these keyboards were designed for a diatonic scale is out of doubt. The question is: were the bars equipped with tangents in order to operate on one string only or more than one?

According to Gerbert’s drawing, all  keys are acting on the three strings simultaneously in order to play a simple melody on the  three strings tuned at the same pitch. No other useful information is offered by the drawing : no indication of drones, no alternative tunings.

Eventually, if we want to extend the c scale, we should tune the lateral strings in c, the middle one  in c'. Then, by lifting the middle string and then the two laterals, (this task carried out by the man in charge of turning the wheel) we can obtain two full octaves.



As we assume that the instrument served to sacred music only, no use of drones have to be admitted, according to western tradition (although many scholars nowadays, influenced by byzantine fashion, perform  gregorian chants also adding drones) 



During the XII century benedictine monks were developing a new technique in polyphonic singing:  

the vox organalis was no longer in parallelum, dismitting the teaching of Musica enchiriadis and Micrologus,  and became freer. 

What was the new instrument role in that new music fashion?

To play the tenor part in organum melismaticum or floridum  for instance, as a ground reference for the upper voice.

A similar role (and similar limits as well) would pertain to the romanesque pipe organ (see J.Ferrando's article in: L'instrumentarium du Moyen Age. Paris, L'Harmattan,2015). 

The geographic area includes Spain and France mainly, then England, Germany, and Italy



At the top of the Gate of Glory in Santiago de Compostela cathedral magister Mateus sculpted a wheel instrument in the middle of the range of the 24 Elders of Apocalypse all around the Lamb. This gate is dated precisely the year 1188. This specimen differs from all others we have examined

  1. In its general shape
  2. In quantity and quality of decorations
  3. Having 11 keys within the octave.

The soundbox consists of two perfect circles connected through lobes and a rectangular box containing the keys. The string length is equal to the circumference of circles. Four triangular sound holes with little holes at the edges are cut in the first circle. A large quadripartite rosette with vegetable decoration is carved in the second circle. An interlace decoration made of 11 knots and 12 spaces is cut all along the rectangular keyboard lid.

Some of these features are unique among all depictions of the instrument. In other articles, I examined these characteristics in the light of musical theory, astronomy, and cosmology of the time. In the present paper I would like to focus on the interpretation of the keyboard with 11 keys within the octave, describing a possible reconstruction of it.

Many important scholars believe that this number indicates a chromatic division of the keyboard. Although they are aware of the fact that no chromatic scale was in use in the 12th-century music, they accept as a piece of absolute evidence that this abnormal chromatic keyboard was used for transposition. This is absurd because no full transposition of any melodic line spanning one octave at least can be made within a single octave! 

My idea is that this setting of keys could be only apparently chromatic and might serve a diatonic scale, this way: two lateral bass strings (a), middle treble string (a') whose nut lies a semitone behind the other two. This pattern works only with this tuning, enlarging Gerbert diatonic scale two tones under the c and reaching the g' of the second octave, including all useful notes of tenor parts in XII century organum melismaticum.

Please look at the next picture: notice the first octave blue (no flat here), the second octave red (chance on 8th bar only between e first octave and f second octave obtained by turning 90° the cilindric bar)



Please, watch the video:




This report gives rise to more doubts than certainties.

Santiago instrument appears to be the more complicated version of a wheel instrument documented for few decades during the 12th century, whose main relevance was due primarily to the continuous sound produced by the wheel, secondarily to the keyboard mechanism. 

We know nothing about the wheel and we assume it was a wooden one with rosin on it. Then we don't know whether the performer used to lift any of the strings from the wheel occasionally or not.

We ignore both the tuning and the keyboard mechanism in detail. It is possible that different solutions have been adopted here and there in different moments and places, including a simpler version with no keyboard at all.

At the beginning of  the XIII century the instrument disappeared.  Wheel instruments survived into smaller forms, playable by one performer, being equipped with a more practical  keyboard, to serve secular music.



A new video:

Read more:



polyphonic keyboard

Organistrum: new polyphonic keyboard

My reconstruction of the instrument is mainly based on my own interpretation of its possible musical function. Since I want to consider it  as a genuine polyphonic instrument I  invented  a  special  keyboard, fit for 12th century two voices polyphonies, suggesting also a different managing of the wheel.


By tuning the strings  either:  A – d – a   or:  A – e – a    we get an overall extension of two chromatic octaves (minus the last semitone). Before lifting each key, the performer  can choose which string he is going to touch, simply by turning the key to the proper position: the first one allows him to operate on the bass string, the second on the middle one, the third on the higher string.

Thus it is possible to play two different melodic lines simultaneously. In Santiago sculpture the hands of the musician on the right are on the third and on the fifth key. This means he is playing  -c, g -  rather than  -d, f -  bichord on bass and middle strings,  or  - g, c’  rather than  - f, d’- bichord on middle and higher strings (first tuning).


First string                              a..       a#      b     c’     c’#     d’

Middle string                         d..       d#      e      f      f#      g    

Bass string                            A..       A#      B     c     c#      d

Keys                                      0          1       2     3       4      5


 In position 4 the key is provided with two tangents so as to act on  second and  third strings (tuned either in Fifth or Fourth)  at the same time to perform  Organum parallelum, leaving the bass string as a drone. 

How they calculated the semitones progression

Known medieval texts neither describe  nor discuss about the possibility of a chromatic scale. But, reading Boethius's De institutione musica, easy to be found in monastic libraries since 9th century on, the monks could learn a lot about semitones both from pythagorean tradition and from Aristoxen's. There are only few lines, but enough, dedicated to the description of Aristoxen's practical method to divide the monochord. From this source the medieval scholar could learn a practical method in order to draw a correct chromatic scale of 12  tempered semitones. We discuss about this in this article:



connecting astronomical and musical  knowledges through 10th and 12th centuries. Anyway, this idea comes from very early roman sources: Plinius and Boethius. In case the author of Santiago instrument intended to describe a revolutionary full chromatic/polyphonic keyboard we can suppose he was aware of that very ancient tradition.



On the other side, the musician who is in charge of turning the crank, by a smooth, even movement of his right hand,  can also lift one or even two of the strings from the edge of the wheel with his left hand in order to stop them vibrating. This way you can either avoid conflicts between the voices or stop  undesired drone effects.  









I chose one big  Red Willow (Salix purpurea) planck, seasoned in nature, from which I  carved the sound box and the base of the keyboard in one piece, average thickness  8-10 mm. Flat back, flat sides as in the original. 

GENERAL MEASURES:                      

 Total length    940mm                                                                                                           

Max width      230mm                                                                                                              

 Depth              80mm                                                                                                                

 Diapason        720mm


In the bottom of sound box I drilled a 10mm hole for the wooden axis, made of Beech (Fagus silvestris). Axis ends into another hole of 10mm drilled directly with no axle box in a wooden bar (Spruce) 15mm thick, glued between the two lobes of sound box which has been carved out of one piece of Spruce (Picea  abies) 8mm thick with no other bars glued underneath. Keyboard  box is independent from the body of the instrument and can be easily removed to modify  general level of the bars, changing their angle with the strings or making reparations. The 11 bars of the keys, diameter 10mm, are of Pine (Pinus nigra) and the 55 pivoting tangents of Beech. The problem of the distances among the bars is discussed in the present article. To avoid noise made by the bars returning to their previous position, after being pulled up to play, a stripe of cloth has been glued at the bottom of the keyboard. The carved lid has been made of Spruce, 8mm thick and is simply interlocked with the body of the keyboard without any hinge or other device.

The wheel, 11cm  wide and 20mm thick is of Walnut (Juglans regia) and forced on  wooden axis without any screw, nail, or wedge. No axle box at the end. The Beech crank , stuck in the square end of the axis, can be easily removed. The soundboard is glued to the body of the instrument , no sound pole in it. The bridge is of Poplar (Populus nigra) reinforced with a Beech edge. The tailpiece  of Chestnut (Castanea sativa) is linked to the bottom of sound box by a leather lace. Tuning pegs are of Beech, no need for a tuning key. Two light  layers of pure almond oil have  been used as  finishing . Gut strings: 0.80, 1.10, 1.40mm.


 Read more:




Subscribe to this RSS feed