The last thing the world may need is another subgenre. What the world could use, though, is one or two solid compilations to define each of the various subgenres that currently occupy — or, more politely, to help adventurous listeners correlate — the ever-increasing number of electronic musicians worldwide. Lowercase (Bremsstrahlung Recordings) is one of the various names (along with “microsound,” among others) given to a realm of music that dances slowly on the precipice of the subsonic. This compilation, by a new San Diego-based label, contains 27 separate tracks by such lowercase leaders as Bernhard Gunter, Steve Roden and Taylor Dupree. Other popular names are notably absent (like Ryoji Ikeda, Oval and Tetsu Inoue), but what lowercase lacks in comprehensiveness it makes up for in other ways. First, it gives us a glimpse of tiny experiments by musicians, like kid606, who are better known for noise than for tenderness. Second, it provides a separate CD-size postcard with detailed biographical and discographical info on each of the 27 cuts’ musicians. Third, for the price of the box set’s two CDs, you get a second copy of the CDs — free. The second set’s envelope reads, “Please pass on to another curious listener,” but you won’t be blamed if you choose to hold on to both sets and mix ’em up at home.