The commentary below is written with "referential authority." That is to say, the authority comes not from this writer but from the documents from the which the information is gleaned and condensed. The referred documents are Tra le sollecitudini, Mediator Dei, Da Musica Sacra et Sacra Liturgia and Rubricarum. The notorious Musica Sacra of 1967 is prohibited in accord with Summorum Pontificum and Universae Ecclesiae.
Read Mass or Missa Lecta
Commonly referred to as “Low” Mass, this form of Mass is more properly referred to as a “Read Mass.” This comes from its Latin name, Missa Lecta. The Mass, in history, would have always been Solemn (see below), but as parishes and villages developed away from monasteries and cathedrals; and as mendicant Orders such as Dominicans and Franciscans, journeyed to preach, priests would desire to offer the Holy Sacrifice for themselves and the souls they found on their journeys. The Missa Lecta was developed for this purpose. It is a quiet and contemplative Mass with one server only, though two can be “tolerated.” The Mass is entirely in Latin, though, in accord with the legitimate Law as prescribed by Pope Benedict XVI, in Universae Ecclesiae the Lesson(s), Epistle and Gospel may be said in the vernacular from an approved translation (at the time of 1962) from the Altar without first being read in Latin. There is normally no music permitted.
Read Mass with Music
Music is not permitted in a Read Mass except in specific circumstances and certain specific rubrics. In fact, a more proper word than permitted would be tolerated, in its classic sense. One may have an organ prelude or postlude and organ music at the Offertory or during Communion in those times of the year where organ music is not prohibited and no solo organ music is permitted in the Mass during Advent, except on Gaudete Sunday or in the season of Lent on Laetare Sunday. No solo organ music is permitted at anytime at a Requiem Mass. Organ music may be used at a Requiem Mass only to support the singing and only if absolutely necessary to even do that. Music or hymn singing may be used at a Read Mass in the following manner. A hymn may be sung as a processional and the recessional and these may be in the vernacular. A Latin hymn may be sung at the Offertory and the Communion but it may not be the text of the Proper of the Mass which must be read by the priest aloud and heard by the faithful in attendance. A hymn may be sung in the vernacular at the Offertory and Communion provided it is connected with the liturgical action. For example, the Offertory hymn could be, “See Us Lord, About Your Altar,” or, “Lord, Accept the Gifts We Offer.” At Communion, the hymn, if in the vernacular, must be a hymn to the Blessed Sacrament or be a hymn of Thanksgiving. The Gloria and Credo cannot be sung at any Read Mass. A Kyrie, Sanctus and Agnus Dei may be sung if they are short, for example, Mass XVI or Mass XVIII, never Mass IX or VIII the Missa de Angelis. These are two long and delay the priest. All singing must conclude so that the action of the Priest is not delayed and the audible texts are not covered by music. The Priest does not sing the Collect or Postcommunion nor any other oration, nor does he chant in any way the salutations, nor do the people respond in chant. These are only said.
Sung Mass—or Missa Canata or Solemn Mass—Missa Solemnis
All Propers must be sung, there are no exceptions. The Epistle and Gospel must be sung, there are no exceptions. All salutations and response are sung, there are no exceptions. If the priest cannot sing the melismatic tones of the Lesson, Epistle or Gospel, then he can chant them recto tono, on the same note. If the Schola cannot manage to sing the Proper chants with the melisma, then it is permissible to sing them in psalm tone, or recto tono. They can also be sung in Polyphony when considered appropriate. At the Offertory and Communion, Latin motets or hymns can also be sung, but only after the Proper Antiphon.
The musical rubrics apply to a Requiem Mass as to the degree above.