To the best of my knowledge, the melody of this chant, "Attende Domine", comes from a 17th century codex while the text comes from a 10th century Mozarabic codex. It speaks of the penitent's admission of his sin and guilt, without ever giving way to depression or despair, wonderfully captured by the joyful yet peaceful melody. The soul, full of trust, confesses its sins and calmly places itself in hands of its Redeemer, knowing, without a doubt, that He will forgive those who are truly sorry for their sins.

Download this song at: https://www.GregorianChantAcademy.com/

Attende Domine

Kocsár Miklós: Beatus Vir

Music: Jacques Berthier
Recorded by Trivium School Chorale (students in grades 7-12)
Paul Jernberg, Director
May 2000
Cathedral of St. Paul
Worcester, MA

Alleluia

Adoramus Te Christe

Magnificat Anima Mea Dominum

Apostles' Creed in Latin - Gregorian chant (Credo in Deum)
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PDF notation and Latin text: https://bit.ly/2KfV8CD
(I begin on G and end on E, as written. However, I interpret the syllable placement at the ends of phrases slightly differently.)
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The Apostles' Creed is the one recited at the beginning of the Rosary, *not* the Nicene Creed normally used during Mass (however, the Apostles' Creed is sometimes used at Mass during Lent/Easter). This prayer is also called "The Symbol of the Apostles" - in Latin, "Symbolum Apostolorum" or "Symbolum Apostolicum."
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Latin text: 

Credo in Deum Patrem omnipotentem, Creatorem caeli et terrae,
  et in Iesum Christum, Filium Eius unicum, Dominum nostrum,
  qui conceptus est de Spiritu Sancto, natus ex Maria Virgine,
  passus sub Pontio Pilato, crucifixus, mortuus, et sepultus,
  descendit ad infernos, tertia die resurrexit a mortuis,
  ascendit ad caelos, sedet ad dexteram Dei Patris omnipotentis,
  inde venturus est iudicare vivos et mortuos.
Credo in Spiritum Sanctum,
  sanctam Ecclesiam catholicam, sanctorum communionem,
  remissionem peccatorum,
  carnis resurrectionem,
  vitam aeternam.
Amen.
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English text:

I believe in God,
the Father Almighty,
Creator of heaven and earth,
and in Jesus Christ, His only Son, our Lord,
who was conceived by the Holy Spirit,
born of the Virgin Mary,
suffered under Pontius Pilate,
was crucified, died and was buried;
He descended into hell;
on the third day He rose again from the dead;
He ascended into heaven,
and is seated at the right hand of God the Father Almighty;
from there He will come to judge the living and the dead.
I believe in the Holy Spirit,
the Holy Catholic Church,
the communion of Saints,
the forgiveness of sins,
the resurrection of the body,
and life everlasting.
Amen.

Apostles' Creed in Latin - Gregorian chant (Credo in Deum)

Rabanus Maurus, recomposed by Gordon Hamilton

A simple, harmonically-engaging setting of Veni Creator Spiritus, based on Rabanus Maurus' 9th century hymn. A solo plainchant singer weaves the traditional melody through a six-part harmonisation.

Download the score: goo.gl/XF5n5E

The Australian Voices
Conductor: Gordon Hamilton

Veni Creator Spiritus

Veni Sancte Spiritus

Libera Me Domine

Los monjes benedictinos del monasterio de Leyre, en Navarra, han querido celebrar al “santo de la vida ordinaria”, al que tanto quieren, con la especialidad de la casa: el canto gregoriano del Oficio Divino. Por eso, han musicalizado los Himnos propios de la festividad de San Josemaría.
+info https://opusdei.org/es-es/article/monasterio-leyre-josemaria-escriva-oficio-divino-canto-gregoriano/

5- Hymnus Ad II Vesperas

https://www.youtube.com/watch?v=xsapS7Qu2Ik
Performance by Organum Ensemble

converto.io

Virga iesse floruit - Gradual of Eleanor of Brittany

Recorded at the Basilica of St. Patrick's Old Cathedral
Basilica Schola
New York City, 12/12
Recorded by Malcolm Addey

14th-century tune; this plainsong version is related to the late medieval Scandinavian version found in Piae Cantiones (1582).

Puer natus in Bethlehem, Alleluia. Unde gaudet Jerusalem. Alleluia. In cordis jubilo Christum natum adoremus, cum novo cantico. 
Hic jacet in præsepio, Alleluia. Qui regnat sine termino. Alleluia. 
 hoc natali gaudio, Alleluia. Benedicamus Domino: Alleluia. 
Laudetur sancta Trinitas, Alleluia. Deo dicamus gratias. Alleluia.

A Child is born in Bethlehem, alleluia. Rejoice together, all Jerusalem, alleluia, alleluia. Refrain: Let us adore the birth of Christ with joyful hearts and a new song. 
He lies here in the manger, alleluia, who rules without end, alleluia, alleluia.  R.
On the joyful day of his birth, alleluia, let us bless the Lord, alleluia, alleluia. R.
The Holy Trinity be praised, alleluia. Let us thank God, alleluia, alleluia. R.

Puer Natus in Bethlehem

A unique choir from a beautiful town in Hungary.

Kocsár Miklós: Beatus Vir

Argenteus Choir