(It.).
In the system of Proportional notation of the late Middle Ages and Renaissance, another name for proportio dupla (time signature 2/1 or more commonly C), where note shapes diminish in relative value in the ratio 2:1. The tactus thus shifts from its normal place on the semibreve (alla semibreve) to the breve. Alla breve still retains its connotation of a smaller relative value per note shape in modern practice, and is commonly used for music in a relatively quick tempo, where C indicates two beats to a bar of four crotchets while C indicates four beats.
PETER WRIGHT