In Martin Gerbert's De cantu et musica sacra  (1774) we find an interesting depiction of the Organistrum.  We can observe in it the mechanism of the keys, the musical scale and the position of the bridge, indicated by the latin word of greek origin: magada. The idea of turning keys, that perform the function of the movable bridge of the monochord is evident, BUT if we make the keys as they appear, in this way, they do not work well on the Organistrum.

If, on the other hand, we think of lever-operated keys that act on the strings from above, pressing them against fixed frets, the mechanism works.

There are a couple of evidences of this mechanism: one is taken from a manuscript of Hildegard Von Bingen's Liber Scivias, another one from Historia del Mundo by Rudolph von Ems (1340).  In both manuscripts the musician is pulling the keys of his Organistrum towards himself using his fingers.

I suppose that Organistrum helped the singers not to loose the right pitches of the fundamental melody in Organum melismaticum.


Watch the videos:

keyboard operation  




Magnus Liber Organi de Notre Dame, XII c.

Florence, Biblioteca medicea, Cod Pluteus, LXIXv.


Nell'opera di Martin Gerbert De cantu et musica sacra (1774) troviamo un famoso disegno dell'Organistrum. Possiamo osservare in esso il meccanismo dei tasti, la scala musicale e la posizione del ponte, indicato dalla parola latina di origine greca: magada. L'idea di tasti girevoli, che hanno la funzione del ponte mobile del monocordo, risulta evidente, MA se si costruiscono i tasti per come appaiono, si scopre che non funzionano bene sull'Organistrum.

Se invece pensiamo a dei tasti a leva che agiscono sulle corde da sopra, premendole contro dei tasti fissi, il meccanismo funziona.

Ci sono due documenti che mostrano questo modello: uno è tratto da un manoscritto del Liber Scivias di Hildegard Von Bingen, l'altro dall' Historia del mundo (1340) di Rudolph von Ems. In entrambi  si osserva che il suonatore tira verso di sè i tasti con le dita.

Credo che un Organistrum così concepito servisse ad aiutare i cantanti a non perdere l'intonazione nell'eseguire la vox principalis dell'Organum melismaticum.


Guarda i video:

funzionamento della tastiera   


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 another blog in this website

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.






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