From the wiki page on the album, bold emphasis mine:
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The album was recorded in February 1974 at the Anaheim Convention Center in Anaheim, California during the group's 1973–74 world tour in support of their fourth studio album, Brain Salad Surgery (1973). Its title comes from the introduction to the show spoken by the show's Master of Ceremonies (Pete Murray, the UK disc jockey) and the opening line of "Karn Evil 9: First Impression, Part 2".
To record the album, staff and equipment were brought in from Wally Heider Studios in Los Angeles, including a 24-track mobile recording unit and a 40-input console. Peter Granet, one of the engineers, called it "the finest recording experience I've ever had".[2] The band used a 4 channel quadraphonic PA system on the tour. A quad mix of the album was released as a three 8-track tape set. A quad LP record edition was planned for release in the Quadradisc format but was scrapped due to engineering issues in master recording which prevented JVC, the manufacturer, from cutting a stable master to meet the format's specifications.
Most of the recordings on the album were first used for broadcast on the American rock music radio show, The King Biscuit Flower Hour. In 1999, the radio recordings were released on CD.
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Are you sure you're not thinking of the album Works Live aka Emerson Lake & Palmer In Concert which was recorded in Montreal in 1977?
Sorry for the late response . I just now read your post.
Yes Steely , I must have been thinking of "Works Live" as you pointed out as the Montreal show.
Interesting that Peter Granet considered the recording as one of his best (up til 73). Kinda flies in the face of what we have as a poor quad mix on at least one third of the recording from Atlantic's Q8 3 pack.
Thanks for the enlightening and informative information.