Langevin was one of the original pro audio manufacturers back in the 50s and 60s. In that era there were far fewer audio manufacturers and Langevin gear was very popular and respected in the broadcast industry. There were very few recording studios then and most of them relied on Langevin, Altec, Fairchild and home-made gear. Early Langevin equipment was vacuum tube based and later became mostly discrete transistor based. Today, you can often find vintage Langevin pieces still working and favored after over 30 years - especially their mic pres!