I’m not sure if this has been talked about somewhere on the forum in the past or not, but Paul Klipsch developed these tapes in the mid 50’s as a way of demonstrating what his speakers were capable of, as there were no reference recordings available to the public at the time. It is really cool to be able to hear these all these years later. They are available in High Res downloads. Links below.

https://www.nativedsd.com/catalogue/albums/hdtt2570-klipsch-tape-reissues-vol-ii...

https://www.klipsch.com/news/klipschtape-release