I want to know the answer to the following question:
Who created the CD-4 format?
All the background I'm provided with is that "A different format, CD-4 (not to be confused with compact disc), by RCA, encoded the front-rear difference information on an ultrasonic carrier, which required a special wideband cartridge to capture it on carefully calibrated pickup arm/turntable combinations.". Is that enough to answer the question?
Answer: yes