Modules from the Eurorack format of modular synthesizers are measured, in terms of width, by what are called “HP.” The letters stand for “horizontal pitch,” which equals a fifth of an inch. Modules are placed alongside each other in cases, and some ingenuity and space-consciousness can be required when putting together a system. You can see such standard modules, out of focus, in the background of the above two photographs. Functional modules are generally between 4HP and 30HP, but start as low as 1HP and seem to get both wider and narrower with each new release, pushing both ends of the spectrum. On the low end, there’s a wide range of 2HP and 3HP devices.
However, the modules can get smaller still. There is a growing number of modules not intended to be in a rack at all, but instead to hover above the rack, held aloft by the very cables that are plugged into them. These are so-called 0HP modules (that is: zero HP). Pictured here are two such ones I recently obtained. On the bottom, from the small company Schenk.work, is the Gerridae, which is named for the water strider bugs. The one up top, from Error Instruments, is named the Flying Attenuator. There’s a company called Mystic Circuits that specializes in 0HP modules. Whether floating or soaring or on the spiritual plane altogether, these add handy functionality without taking up any precious room.