The four Marian Antiphons (Alma Redemptoris Mater, Ave Regina Cælorum, Regina Cæli, and Salve Regina) have traditionally been sung at the end of Compline (Night Prayer) – each one during a particular season of the Church Year. Alma Redemptoris Mater is sung from the first Sunday of Advent until the Feast of the Presentation of Our Lord (Candlemas) on 2nd February.
Here is the music for Alma Redemptoris Mater and a recording.
A&B Liturgy 