De Musica Sacra:
Quote:
C. Sacred instrumental music.
68. Other instruments besides the organ, especially the smaller bowed instruments, may be used during the liturgical functions, particularly on days of greater solemnity. These may be used together with the organ or without it, for instrumental numbers or for accompanying the singing. However, the following rules derived from the principles stated above (no.60) are to strictly observed:
a) the instruments are truly suitable for sacred use;
b) they are to be played with such seriousness, and religious devotion that every suggestion of raucous secular music is avoided, and the devotion of the faithful is fostered;
c) the director, organist, and other instrumentalists should be well trained in instrumental techniques, and the laws of sacred music.
Also, St. Pius X wrote that woodwind instruments could be used in mass with the permission of the ordinary.
http://www.cathinfo.com/catholic.php?a=topic&t=30333&min=10&num=5