The four-hymn sandwich. It is a nickname for the structure of music at most Masses in the United States over the last forty years, perhaps not a complimentary one. You know them: the entrance, offertory, Communion, and recessional hymns.
You may be surprised to learn that hymns are not part of the Mass. Before 1965, the congregation might be given a hymn to sing at one or two places in the Mass, because there was nothing else for them to do - the priest alone had all the prayers, in Latin, often inaudibly, and for long stretches of time. But after the changes of the Second Vatican Council, the texts of the Mass were suddenly available in the local language - English in our case – but there was no music for them. Catholics had always sung the prayers and texts of the Mass, but in the rush to abandon Latin this practice was lost. So people became accustomed to singing hymns and songs instead.
These hymns and songs inserted were from many sources; some old ones both Catholic and Protestant, and some newly written. Their suitability for the Catholic Mass, as well as their musical and theological value, was uneven at best. The reason the Protestants have so many hymns is that their Sunday worship lacks the sacramental, liturgical character that marks the Church's worship, so those hymns, while splendid, do not necessarily enhance the Mass.
Having grown up entirely in this time of liturgical transition, I have personally experienced almost every attempt that has been made to apply music to the Mass in English. Some were more successful than others. One of the things that has bothered me since I was a little kid was the insistence that a communion song be sung by the people while they are receiving Holy Communion. It was obvious to me as a twelve-year-old, and ever since, why so few people would actually sing then. First, it is a logistical challenge to carry and read the music while moving toward the Eucharist. Then, having received, it is no longer possible to sing - it would be the liturgical equivalent of talking with our mouth full!
The other hymn I began to wonder about more recently is the recessional. It struck me once I was a priest celebrant that I didn't know whether I was supposed to leave as soon as the hymn started or wait at the chair or in front of the altar, so I could sing the whole hymn, then walk out. You all know how much I enjoy singing; that wasn't the problem. But it wasn't only a problem for me; people didn't know what to do. The priest says mass is over, go - but then, there's more to do! At the Basilica of the National Shrine, they print a little admonition to respect their tradition and stay until the hymn is finished. That didn't satisfy me either. The Mass is truly over - look in the missal: after the dismissal, the priest and ministers depart, and that's all there is. Why add something? It would seem that everyone else can depart too - though etiquette has always been that the people wait at least until the priest has left.
I encountered a solution to both these hymn dilemmas at a friend’s parish in Greenville, South Carolina. Instead of singing during Holy Communion and after the end of Mass, have one hymn after everyone has received the Eucharist, before the Prayer After Communion concludes the Communion Rite. Hands and mouths are free to sing a hymn of praise and thanksgiving. Then, after the prayer and dismissal (and perhaps some announcements) it is only a moment before the dismissal and the true end of Mass - the priest exits, and so can everyone else. There is no conflict about whether to sing or depart or anything else, only some walking-out music for everyone, called a Postlude. It is both more practical and more liturgical.
And best of all, Mass begins to look more like the Mass and less like a sandwich.