Here are some thoughts on the specific elements you mentioned:
Target audience: You're right that the album could appeal to fans of soft rock, heavy metal, jazz fusion, and even hard rock. It's got something for everyone, with catchy melodies, intricate instrumental passages, and Zappa's signature brand of humor and satire.
Ralph Humphrey's drumming: Humphrey's drumming is indeed the epitome of "relaxed under pressure." He manages to keep things grooving even when the music gets really weird, and his fills and solos are always tasteful and creative.
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Ralph Humphrey drummer
Ruth Underwood's percussion: Underwood is a true percussion wizard, and she's definitely given some of the most challenging parts on the album. Her marimba and vibraphone work is amazing, and she even throws in some timpani and xylophone for good measure.
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Ruth Underwood musician
Horn section: The horn section on Over-Nite Sensation is fantastic. They add a layer of richness and complexity to the music, and their solos are always a highlight. The comparison to Woody Herman and Stravinsky is apt, as they manage to sound both playful and sophisticated.
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Horn section
Comparisons to Xenakis and Varèse: I think it's fair to say that Over-Nite Sensation shares some similarities with the works of Iannis Xenakis and Edgard Varèse. Both composers were known for their use of dissonance and complex rhythms, and Zappa was definitely influenced by their work. However, Zappa's music is always more playful and humorous than that of Xenakis and Varèse.( FIFA coins)
Overall, Over-Nite Sensation is a classic album that stands the test of time. It's a testament to Zappa's genius and creativity, and it's no wonder that you were so impressed by it as a young musician.