Actually, the main Sunday Mass, pre-Vatican II, was supposed to be a Sung Mass (Missa Cantata) while daily Masses were Low Masses. The "special occasion" Masses would have been Solemn High Masses which had a priest celebrant, a deacon, and a subdeacon and musical accompaniment. This was the ideal. It may not have been the reality in every parish.
I can point to a few dozens of parishes in Milwaukee which maintained two or three choirs (the adult choir being one, then one or two grade-school choirs) which sang for the Sunday and daily 'missa cantata' prior to 1965.
Milwaukee was unusually blessed, as the godfather of church music up here (John Singenberger) was educated at Regensburg, the home of the last major Church music reform (1880's.)
He stopped briefly in Cincinnatti, then came here and taught at the Seminary, but also was responsible for promoting good parish-level church music programs all around the Diocese. He was also regarded as a 'pretty-good' composer of church music; a good deal of his ouevre is still used in Milwaukee.
Milwaukee had a very active group of parish musicians which met regularly and during every other summer would also have a 3-day seminar; guest lecturer/workshop leaders included Roger Wagner and Paul Salamunovich, not to mention our own Sr. Theophane (Hytrek), OSF.
After 1965, but particularly after the arrival of Rembert, the deterioration in standards and mission was clear. Now we see parish "directors of music" whose BS in Knitting Arts and continuing education in "music" consists of learning about maracas and Bo Diddley hits.
The only "sung" Sunday Masses I ever attended were at the Newman Hall at the University of California -- Berkeley. It was beautiful, but definitely not the norm in the Parishes. The liturgy was called the Congregational High Mass.
I lived quite a distance from the Newman Club and we had to walk. If you arrived a wee bit late, they were already singing and the sounds of the voices wafted out the windows and down the stairs. The stairs were heavily carpeted and that sort of muted the sound of the singing as you tiptoed upstairs to take your place in a back pew. It was almost magical.
The worship space was paneled in dark wood -- walnut or dark oak. And the massive boxed beams holding up the roof were done in a trinity design with 3 holes constructed in the center of each beam where they met the peack of the roof and a similar design at the ends where the beams flared to meet the walls. The exterior was dark brick with burned and twisted bricks added every so often, protruding from the walls. It was the most beautiful building.
They demolished it in 1963 and replaced it with an ugly engineering building. I would have given anything to have salvaged a brick from the rubble -- but such was not my luck. Newman Hall moved across campus and they built a poured concrete semi-circular very sterile appearing building. The altar became a mound, and the altar accoutrements -- crucifix, priest's chair, altar table -- look like something out of Stonehenge, or Barney Rubble.
The building is semi-circular because one neighboring property owner refused to sell because he hated the Catholic Church and he added a provision to his deed that the land could never be sold to them. So, the Paulists had to change the design of the new church and it became 3/4 of a circle instead of a full circle.
In any case, I never attended a Parish anywhere else with music at Sunday Mass until after Vatican II. And I can count at least 6 parishes in two states. At first it seemed very odd to have regular parishioners standing up front leading the singing. And the day a visiting priest assigned to our parish from Malta played the violin for Easter services was simply amazing. He also composed an original Our Father (music) for our parish and gave it to us to use forever after -- copyright free. (St. Leo's in Oakland, CA.)
Later I moved to Texas, and we didn't have any music there either. It took my daughter hauling an old organ out of the closet (she was 14) and teaching herself to play before we had music at regular masses. Later the parish bought a beautiful organ and hired an organist after my daughter left for college, but my daughter played for all the traditional masses and weddings until that time. We did have a folk choir with guitars for one Mass a week, but that was the only music.