Each "O" antiphon can be easily set to the Magnificat tune of the Hymnal by using the colon as the separation between the two half verses, and assigning the first two syllables of each half verse to the intonation notes of each line of the Magnificat.
If one desires to chant these antiphons to the ancient psalm tones, every antiphon is chanted according to the solemn tone 2D, see below for an example.
Here is another the ancient solemn tone set to the key of F major. Each note of the intonation, mediation, and termination is sung to a separate syllable. Syllables falling on slurred notes are sung to two notes.
If one desires to chant them according to the ancient tones, they may be render as such:
a) Antiphon, chanted by Cantor; Magnificat, chanted by choir in unison; Antiphon, chanted by Cantor.
b) Antiphon, chanted by choir in unison; Magnificat, sung to the tune in the hymnal*; Antiphon, chanted by choir in unision.
This gives this part of the liturgy a true antiphonal nature, i.e., responses back and forth between two groups, or persons.
Catch the O Antiphons in real time starting today, December 17, over at LutheranTimeOut.org. Hear them first at Noon ET on piratechristianradio.com, and then at your convenience later after 12:15 pm ET on Time Out's website.
Visit St. Matthew Evangelical Lutheran Mission in Mayer, Minnesota where Deacon Dulas. This mission post is about 1 hour west of Mall of America and about 1 hour northwest of Shakopee.
*The psalm tones are compatible with the Magnificat in Vespers in TLH, LW, and LSB. If you sing the 2nd tone in the key of C, you can use it with LSB's Evening Prayer in place of the printed antiphon. Over at lcms.org you can find audio files of LSB's Matins and Vespers. Click here for the direct link to the Magnificat, beginning with the response, "Let my prayer rise..."