Frac rack

Frac is a modular synthesizer format. Frac is sometimes referred to as "Frac Rack". Like the Euro format, Frac is considered a 3U format. The height of most modern modular synthesizer modules is measured by the number of vertical units it consumes in a standard 19" equipment rack. Modules conforming to the 3U format, for example, will take up three vertical units in a 19" equipment rack. Frac format modules typically use (1/8") connectors and plugs for patching, although there are several companies that offer banana jacks (BugBrand, Metalbox).

Manufacturers of Frac format synthesizer modules include PAiA, Blacet Research, Metalbox and BugBrand.