About Cantus Organi

Organ accompaniment to Gregorian chant, with music for both the Extraordinary Form and Ordinary Form at the console.

What it is for

Nova Organi Harmonia ad Graduale Romanum was published by the Lemmens Institute at Mechelen in 1942: eight volumes of organ accompaniment for the whole of the Gregorian repertoire of the Mass and of Sunday Vespers. It is in the public domain, but in print it is rare and scattered, and finding the right page for a given Sunday means knowing which volume holds it.

This site puts the scanned pages online, divided into 576 pieces, and ties them to the calendar of the 1962 Missal and the Ordinary Form calendar, so an organist can go from a date to the music for that day's Mass and Vespers. Nothing is re-engraved: every system of music is an image of the printed page, with its printed page number.

How to use it

Find the music for a day

Open the Calendar and choose a date. The day's page lists the Proper of the Mass (Introit, Gradual, Alleluia or Tract, Offertory, Communion), the Ordinary it suggests, and its Vespers. Each part has a link straight to its place in the music.

The Ordinary Form calendar assigns the chants of theGraduale Romanum (1974) and links each chant to an NOH accompaniment when the same music is printed there. The assigned chant and the available accompaniment are separate facts: a missing accompaniment is labeled, and an occasion whose assignments are not yet mapped says so.

Vespers

For Sundays and feasts, the Vespers pages give the whole office in the order sung — the opening versicle, the five psalms with their antiphons, the chapter, hymn, versicle, Magnificat and the seasonal Marian antiphon — built for each date from 2025 to 2031. I Vespers of the greater feasts have their own page, for the evening before. Where the book prints only the opening of a psalm, the page says which formula to continue with and gives the psalm's text; where it prints no accompaniment in a tone at all, the page says so rather than guess.

Browse the books

The home page lists the books as printed: the Proper of Time, the Proper of Saints, the Common, the Kyriale, the Masses for the Dead, the Vesperale, and votive Masses. Search finds a piece by its title or opening words.

At the organ

Invert (top of every page) switches the page and music to a dark theme, for a dark organ loft. The setting is remembered on that device.
Export PDF makes a file of the pages you need, to print or to keep on a tablet on the music desk, on US Letter or A4 paper (the choice is remembered). Parts shown typeset go in as the typeset music; parts switched to the scans go in as scans.
Chant links open the melody on GregoBase; on pages that offer it, the switch Show the chant draws the chant above the accompaniment.
Chant text expands sourced Latin lyrics beside the music, where available.
Pages print cleanly: the menus and buttons are left off the paper.

What it does not do yet

The Extraordinary Form calendar follows the 1962 rubrics. The Ordinary Form calendar covers the General Roman Calendar with switches for the Epiphany, Ascension and Corpus Christi transfers; it is not a national or diocesan calendar.
Ordinary Form chant assignments follow the pinned jgabc data and reviewed overrides for the 1974 Graduale Romanum. They do not establish that a chant is printed in NOH. Missing accompaniment and unmapped assignment notices are kept distinct.
Vespers is built for Sundays and I and II class feasts that the book prints. A few feasts that fall on a Sunday only in some years (the Transfiguration, the Holy Cross, St Michael) have no Vespers page, because the book has no section for them.
Some Magnificat and psalm tones are not printed in the Vesperale; those are marked on the page to be sung unaccompanied or improvised.
Parts of the catalogue were matched by machine and have not all been checked by eye.

Errors and corrections

If a piece is on the wrong page, a title or mode is wrong, or a chant link points at the wrong melody, please say so on the Corrections page. Every report is read and fixed by hand.

Editors review reports and make corrections on the admin screen (sign-in required).

Typeset music

Where volunteers have transcribed a piece, the site shows it typeset instead of the scan: clearer on a small screen, and sharp when printed. The transcriptions are the work of Joe Egan and the volunteers of the nova-organi-harmonia project, drawn here with LilyPond.

Everything typeset is marked not yet proofread until an editor has checked it against the book. Show the scans at the top of the page swaps every part back to its scan (your browser remembers the choice), and Show the scan under a part swaps just that one. If the typeset music differs from the scan, the scan is right: please report it.

Sources and attributions

Nova Organi Harmonia ad Graduale Romanum: Lemmens Institute, Mechelen: H. Dessain, 1942. The page images and everything cut from them are in the public domain.
nova-organi-harmonia: The LilyPond transcriptions behind the typeset music, by Joe Egan and the project's volunteers, imported at a fixed commit and credited wherever they are shown.
GregoBase: The chant melodies shown with each part and linked from it. Released under CC0.
Exsurge: Draws the chant notation in the browser. MIT licence, © 2016 Fr. Matthew Spencer, OSJ; maintained by Benjamin Bloomfield.
jgabc: Which chants make up each day's Proper. The pinned propersdata.js source supports the 1962 calendar; propersdatanovus.js supplies Ordinary Form assignments based on the 1974 Graduale Romanum. Both are under the Unlicense. Its assignment data can link a chant to a NOH source, but cannot correct NOH catalogue records or assert that every chant has an accompaniment.
Missalemeum: The 1962 calendar: which Mass is said on each date. MIT licence.
Divinum Officium: The texts of Vespers — antiphons, psalms, chapters and hymns — and which are said on each day. MIT licence.
vesperale: Fr. John Jenkins's Vespers booklets, whose table of Magnificat antiphons and tones was used to check this site's.
Pagefind: The site search. MIT licence.
Verovio: Lays out the typeset music again when you customize an export. Version 6.3.0, used unmodified and loaded as a separate file only when the export editor opens. Licensed under theGNU LGPL 3.0 or later, which extends theGNU GPL 3.0;source code for this version.
Liberation Serif: The lyric and heading type in customized exports.SIL Open Font License 1.1.

The site itself, its code and its hand-made indexes of the books are released under CC BY-SA 4.0, and are on GitHub, so the work can be copied and carried on.