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 from contemporary notation. Compositions written in mensural notation should use the Mensural MEI module. The MEI Translator encodes CMN-MEI files created with Sibelius to Mensural MEI files.

The Sibelius transcription of the pieces follows a set of rules developed by Karen Desmond. Examples of the rules are:

• staccato marks to show the dots present in the manuscript (both of division or perfection)
• tenuto marks to show downward stems in the manuscript that represent longer semibreves in ars antiqua
• tremolo marks for plicas, etc.

Implementation

The project consist on three modules: (1) arsantiqua, (2) arsnova, and (3) MEI_Translator. The first two modules contain functions that deal with features characteristic from one of the two Medieval musical styles: 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 MEI_Translator module contains general functions for the translation, shared by both Ars antiqua and Ars nova styles. The user can run the module as a script, along with piece name, music style, and mensuration value parameters.

Requirements

• The LibMEI library. The wiki contains instructions on both the installation of the LibMEI C++ library, and the installation of the python bindings.

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, two values: "antiqua" and "nova"

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 pieces (musical style = "nova"), while the -NewVoiceA flag is use only for Ars antiqua pieces (musical style = "antiqua").

New voice flag in Ars nova: -NewVoiceN

Use this flag for each new voice (Ars nova) 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.

Example:

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

New voice flag in 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.

Example:

-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 MEI_Translator.py TestFiles/IvTrem/zodiacum.mei nova -NewVoiceN i p i p -NewVoiceN i p i p -NewVoiceN i p i p

Ars antiqua piece - Sicut from the Fauvel:

$ python MEI_Translator.py TestFiles/Fauv/sicut.mei antiqua -NewVoiceA 3 p -NewVoiceA 3 p -NewVoiceA 3 p

You can also go to the TestFiles directory and run:

$ python processing.py

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

Using the module

As 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()

2. 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, "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 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 MEI elements were actually removed in the translation process, like the tie and mRest elements. Since mensural notation does not use ties nor 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:

cmn_meidoc.getElementsByName('tie')
mensural_meidoc.getElementsByName('tie')

The second method returns a blank list with either the tie and mRest elements provided as argumetns. The script converts all mRest elements into simple rest elements. You can actually verify the outcome 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), and returns a list of notes along with its mensural parameters: "imperfection", "alteration", "perfection", "partial imperfection" or "major semibreve". You can pass any 5 string-values as a parameters to the method in order to return a list of notes with its mensural modificaton type, or you can omit the parameters to get a list of notes modified by any of those five modification types.

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

import pymei

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

from MEI_Translator import MensuralTranslation

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

The "partial imperfection" modification only occurd in Ars nova 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, "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 MensuralTranslated 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 MensuralTranslated object mensural_meidoc use the following code:

pymei.documentToFile(mensural_meidoc)

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 MensuralTranslated object), and convert it to a file with pymei.documentToFile().

Notes

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 MEI_Translator.py TestFiles/IvTrem/bona.mei nova -NewVoiceN i p i p -NewVoiceN i p i p -NewVoiceN i i i p