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MEI_Translator: from CMN-MEI to Mensural-MEI

The MEI_Translator script takes a CMN (Common Music Notation) MEI file and translates it into a Mensural MEI file.1 It was developed for mensural music that was transcribed in Sibelius, and exported to MEI files with the sibmei plugin. MEI files generated with Sibelius are CMN-MEI files. The CMN-MEI module encodes music in contemporary notation. Compositions written in mensural notation should use the Mensural MEI module. The MEI Translator translates CMN-MEI files created with Sibelius to Mensural MEI files.

The Sibelius transcription of the pieces follows conventions developed by Karen Desmond. For further background on the project, see The conventions followed for the modern transcriptions can be found in the 'About' page in the 'Encoding Process' section. In this section (third point) you can find the list of the articulation marks used to represent mensural notation features that are usually not represented in modern transcriptions (e.g., alterations and dots of division).


The CMN-MEI_to_MensuralMEI_Translator project has four modules: (1) arsantiqua, (2) arsnova, (3) white_notation, and (4) MEI_Translator. The first two modules contain functions that deal with features characteristic from one of the two medieval styles of notation: ars antiqua and ars nova. The arsnova module deals with "partial imperfections," and considers "minims" and "prolatio", while the arsantiqua module considers the presence of "major semibreves" and "duplex longas." The third module deals with white mensural notation. It is very similar to the arsnova module, but it includes support for smaller note values (i.e., semiminima, fusa, and semifusas) and hemiola coloration, which were included in the late fourteenth century and were frequently used during the Renaissance.

The MEI_Translator module contains general functions for the translation, shared by the three ars antiqua, ars nova, and white mensural styles. The user can run the module as a script, along with piece name, music style, and mensuration value parameters.


Software requirements

  • The LibMEI library. The wiki contains instructions on both the installation of the LibMEI C++ library, and the installation of the python bindings.
  • The SibMEI plugin. Follow the Download and Installation instructions of the README. The SibMEI plugin will allow you to export your Sibelius transcription of the piece into the CMN MEI that is used by the Mensural MEI Translator.

Encoding requirements

  • Follow the guidelines in regarding the use of articulation marks to represent certain mensural notation specificities that are usually not captured in modern transcriptions.
  • If you are transcribing an ars antiqua or an ars nova piece, you need to bar it by the long for the Mensural MEI Translator to work properly.
  • If you are transcribing a white mensural piece, you need to bar it by the breve for the Mensural MEI Translator to work properly.

Running the script

Parameters are set according to a composition's musical style. The two parameters that are common for both styles are:

  • the piece name, or the path to the piece if the composition is in a different directory than the script
  • the musical style, three values: "ars_antiqua", "ars_nova", and "white_mensural"

Other parameters indicate the mensuration for each of the voices in a composition. Use the following two flags to enter the mensuration definition for each voice: -NewVoiceN and -NewVoiceA. The -NewVoiceN flag is used exclusively for ars nova and white mensural pieces (musical style = "ars_nova" or "white_mensural"), while the -NewVoiceA flag is used only for ars antiqua pieces (musical style = "ars_antiqua").

New voice flag for ars nova and white mensural notation: -NewVoiceN

Use this flag for each new voice (ars nova or white mensural) that you are entering. After the flag, use the characters p or i to indicate the mensuration of one voice in the order: modus major, modus minor, tempus and prolatio. Medieval theorists would refer to ternary prolation as 'major' and a binary prolation as 'minor', but the labels 'p' and 'i' are continued for prolation, for simplicity's sake.


-NewVoiceN i p i p indicates a voice with imperfect modus major and tempus, and perfect modus minor and prolatio.

New voice flag for ars antiqua: -NewVoiceA

Use this flag for each new voice (ars antiqua) that you are entering. After the flag, use the characters 2 or 3 to indicate the division of the breve, which can be duple or triple, and then use the characters p or i to indicte the modus minor.


-NewVoiceA 3 i indicates a voice with 3 minor semibreves per breve (triple division) and imperfect modus minor.

The order in which you enter the mensuration of the voices using the new voice flags (-NewVoiceN or -NewVoiceA) should be the same as the order of the voices in the CMN MEI file (or the Sibelius file).

Examples with more than one voice:

-NewVoiceN i i p p -NewVoice i p i p -NewVoiceN p i i i is used for an ars nova 3-voice piece with different mensurations for each voice.

-NewVoiceA 2 p -NewVoiceA 2 p -NewVoiceA 2 p -NewVoiceA 2 p is used for and ars antiqua 4-voice piece with the same mensuration for all its voices (duple divison of the breve and perfect modus minor).

Examples of running scripts at the command line

Here are two pieces, one for ars nova and one for ars antiqua. The composition are included in this repository (TestFiles directory).

Ars nova piece - Zodiacum from the IvTrem:

$ python TestFiles/IvTrem/zodiacum.mei ars_nova -NewVoiceN i p i p -NewVoiceN i p i p -NewVoiceN i p i p

Ars antiqua piece - Fauvel from the Fauvel:

$ python TestFiles/Fauv/fauvel.mei ars_antiqua -NewVoiceA 3 p -NewVoiceA 3 p -NewVoiceA 3 p

You can also go to the TestFiles directory and run:

$ python

The script above runs all the instructions contained in the IvTremPieces.txt and/or FauvPieces.txt files, which run the MEI_Translator over all the pieces in the IvTrem and/or Fauv directories, respectively.

Using the module

We saw in the previous section how to run the MEI_Translator as a script. But the MEI_Translator can also be used as a module.

Here are the steps to follow in order to use the MEI_Translator as a module. To illustrate each step we are using bona.mei from the IvTrem as an input file.2

  1. On your python shell, import the pymei module and convert your piece into a pymei.MeiDocument object.
import pymei

cmn_meidoc = pymei.documentFromFile("TestFiles/IvTrem/bona.mei").getMeiDocument()
  1. Import the MEI_Translator module and create a MensuralTranslation object, which will inherit all the methods from the pymei.MeiDocument class.
from MEI_Translator import MensuralTranslation`

mensural_meidoc = MensuralTranslation(cmn_meidoc, "ars_nova", [["i", "p", "i", "p"], ["i", "p", "i", "p"], ["i", "i", "i", "p"]])

Now you will be able to use all the pymei.MeiDocument methods (getElementsByName, getElementById, etc.) and a new method included in the MensuralTranslation class (getModifiedNotes) to be able to access elements in the file and edit them before you call the function documentToFile to create the file containing the Mensural MEI document.

MeiDocument inherited methods:

We can use the inherited methods from pymei.MeiDocument to check that certain MEI elements were actually removed in the translation process, like the tie and mRest elements. Mensural notation does not use ties and, as it doesn't have measures, the Mensural-MEI module doesn't recognize mRest elements (measure rests). We can check if the tie elements present in the CMN-MEI document are still present in the Mensural MEI document by using:


The second instruction returns a blank list. Same thing will happen with the mRest elements. Actually, the script converts all mRest elements into simple rest elements; you can verify this by using the following code (which should return True):

len(cmn_meidoc.getElementsByName('rest')) + len(cmn_meidoc.getElementsByName('mRest')) == len(mensural_meidoc.getElementsByName('rest'))

Additional methods:

The getModifiedNotes() method returns a list of notes that have been modified from its default value (the value given by the mensuration). There are only 5 possible modifications: "imperfection", "alteration", "perfection", "partial imperfection" or "major semibreve". You can pass any of these five string-values as a parameter to the method getModifiedNotes() in order to get the list of notes from the piece with this particular modification; or you can omit the parameter and get a list of all notes modified by any of these five modification types.

Since "major semibreve" is a modification that occurs only in ars antiqua, you could run the following code to see the method working:

import pymei

cmn_meidoc = pymei.documentFromFile("TestFiles/Fauv/fauvel.mei").getMeiDocument()

from MEI_Translator import MensuralTranslation

mensural_meidoc = MensuralTranslation(cmn_meidoc, "ars_antiqua", [["3", "p"], ["3", "p"], ["3", "p"]])
mensural_meidoc.getModifiedNotes('major semibreve')

The "partial imperfection" modification only occurs in ars nova (and white mensural) pieces. Here is an example:

import pymei

cmn_meidoc = pymei.documentFromFile("TestFiles/IvTrem/zodiacum.mei").getMeiDocument()

from MEI_Translator import MensuralTranslation

mensural_meidoc = MensuralTranslation(cmn_meidoc, "ars_nova", [["i", "p", "i", "p"], ["i", "p", "i", "p"], ["i", "p", "i", "p"]])
mensural_meidoc.getModifiedNotes('partial imperfection')

Getting the Mensural MEI File: the documentToFile function

Because the MensuralTranslation object is already instantiated, it behaves just like a regular MeiDocument. You can also edit any of the elements. To generate a file use the documentToFile function from the pymei module (already imported). To obtain the Mensural MEI file from your MensuralTranslation object mensural_meidoc use the following code:


You receive the same outcome as from the MEI_Translator script, except that you are still able to modify the Mensural MEI document (with the MensuralTranslation object), and convert it to a file with pymei.documentToFile().


1: Common Music Notation here refers to music notation in current use, aside from graphic music notation, and not the Lisp-based open-source music notation software.

2: Alternatively, you could run the MEI_Translator as a script on the command line to obtain the Mensural MEI file for this piece directly by entering:

python TestFiles/IvTrem/bona.mei ars_nova -NewVoiceN i p i p -NewVoiceN i p i p -NewVoiceN i i i p


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