Nicene and Post-Nicene Fathers, Ser. II, Vol. XIV:
The Canons of the Councils of Ancyra, Gangra, Neocæsarea, Antioch and Laodicea, which Canons were Accepted and Received by the Ecumenical Synods.: Canon XV

Canon XV.

No others shall sing in the Church, save only the canonical singers, who go up into the ambo and sing from a book.

Notes.

Ancient Epitome of Canon XV.

No one should ascend the ambon unless he is tonsured.

Hefele.

The only question [presented by this canon] is whether this synod forbade the laity to take any part in the Church music, as Binius and others have understood the words of the text, or whether it only intended to forbid those who were not cantors taking the lead.  Van Espen and Neander in particular were in favour of the latter meaning, pointing to the fact that certainly in the Greek Church after the Synod of Laodicea the people were accustomed to join in the singing, as Chrysostom and Basil the Great sufficiently testify.  Bingham propounded a peculiar opinion, namely, p. 133 that this Synod did indeed forbid the laity to sing in the church, or even to join in the singing, but this only temporarily, for certain reasons.  I have no doubt, however, that Van Espen and Neander take the truer view.