Sung and Spoken Masses
There are two basic forms of the Latin Mass: the Sung Mass and the Spoken Mass. The Sung Mass is also known as the High Mass, because the priest sings in a "high" (loud) voice, and the Spoken Mass is also known as the Low Mass, because the priest speaks in a low (soft) voice. This distinction is the most fundamental, but it is not the only distinction we can make regarding different "types" of Masses. Private vs. Public Masses, the Conventual Mass, the Mass of the Pre-Sanctified, and others reveal the ways in which the Mass can take on different "characters" depending on certain circumstances or needs.
The Sung Mass is most ideal, as singing is the most ancient and most fitting way of offering the Divine Sacrifice. Singing the Mass "decorates" it in such a way as to make it reflect the Heavenly liturgy, giving it more depth and beauty. And it is indeed the case that the Sung Mass predates the Spoken Mass, such that we can actually see the liturgy beginning as a complex event happening once a week and, over time, becoming celebrated more frequently with less ceremony and singing. As Masses multiplied per week (beginning perhaps in the third century), it became impractical to have a choir always present, and the priest resorted to speaking the parts of the Mass, including those the choir would have sung.
The Multiplication of Masses
The multiplication of Masses per week occurred principally in the West, and it was driven by the practice of offering Mass for the dead. The more Masses offered, the more grace was made available to the souls for which they were offered. Thus, though with Pope St. Gregory the Great in the late 6th century we find the practice of offering Mass once every Sunday predominating in Rome, by the beginning of the 9th century, we have the example of Pope Leo III offering perhaps 8 or 9 Masses per day. This practice also encouraged the multiplication of altars in single church, which further discouraged frequent Sung Masses, as priests might often say Mass simultaneously at different altars, for which the Low Mass was especially suited.
East and West
Churches in the East continue to have only one altar, though eastern practice allows for concelebration (the offering of the Victim by more than one priest together). Churches in the West originally also had only one altar, located at the crux of a cross-shaped church. Over time, altars were added along the walls of the church, though there remained a main altar - the high altar. However, not until after the Second Vatican Council was concelebration generally allowed in the West.
Though the Church limited the number of Masses a priest could say in one day by the 14th century, this practice had a great impact on western spirituality. We can see an example of this in the Irish influence on American Catholicism, which is heavily marked by the tradition of the Low Mass that it received from Irish immigrants. However, in the current revival of the use of the Latin Mass, we more often see it celebrated as a Sung Mass, and this is the ideal.
