Wikipedia
Haeco-CSG
The Haeco-CSG or Holzer Audio Engineering-Compatible Stereo Generator system is an analog electronic device and method developed by Howard Holzer. His company, Holzer Audio Engineering, developed the system in the 1960s during the years of transition from monaural to stereophonic popular music recording. The process was used primarily from about 1968 until 1970 but still exists on a significant number of recordings made during the time.