like all Church Documents there is wiggle room, but the most clear statement is in “Liturgical Music Today” (1982, Bishops’ Committee on the Liturgy) paragraphs 60-62:
60 The liturgy is a complexus of signs expressed by living human beings. Music, being preeminent among those signs, ought to be “live”. While recorded music, therefore, might be used to advantage outside the liturgy as an aid in the teaching of new music, it should, as a general norm, never be used within the liturgy to replace the congregation, the choir, the organist or other instruments.
61 Some exceptions to this principle should be noted, however,. Recorded music may be used to accompany the community’s song during a procession out-of-doors and, when used carefully, in Masses with children. Occasionally it might be used as an aid to prayer, for example, during long periods of silence in a communal celebration of reconciliation. It may never become a substitute for the community’s song, however, as in the case of the responsorial psalm after a reading from Scripture or during the optional hymn of praise after communion.
62 A prerecorded soundtrack is sometimes used as a feature of contemporary “electronic music” composition.When combined with live voices and/or instruments, it is an integral part of the performance and, therefore, is a legitimate use of prerecorded music.
(Taken from “The Liturgy Documents - a parish resource” (LTP Chicago, 1985).