Trimicron

Trimicron was the name used by French record company MDR (Magnetic Disc Recording) in the mid seventies to denominate their experimental technique (devised by Dr. E. Rabe) of completely removing the gap between each turn of the spiral created by the groove of a record. On average, this gap corresponds to the space occupied by two turns of the groove spiral. With this gap removed, a record can hold triple the information that it usually does. That's why Trimicron records, marketed as "triple durée", are the longest-playing 12-inch 33 1/3 RPM records ever produced, with close to one hour of music per side. This technique was intended for classical music fans to enjoy complete works without having to flip the record. Trimicron records enjoyed an ephemeral success, since the convenience of longer playing time also resulted in a significant drop in the overall volume of the recordings (which means more prominent background noise). Also, because of the groove turns being so close together, only very well-setup record players with unworn styli could play them properly (without skipping). A catalog of almost 30 Trimicron LPs is known to exist.