Alley is a musical notation similar to alga and its synonym, Allah. However, whereas when orchestra members reach alga or Allah in their musical score they must put aside their instruments if necessary and chant “ah,” when they see alley in their score they must screech “ey” (pronounced “eeeeyyyy”), again first putting aside their instruments if necessary.
It is no more difficult for players of wind instruments to perform an alley as an alga. But, screeching an alley is widely considered to be even less dignified than chanting an alga. That’s why they pay orchestra members the big bucks.