Considering the criteria established -instrumental originality
, sound exploration
, lyrical content
& lasting influence
-, I'd say "Tomorrow Never Knows" (from 1966, by The Beatles) (currently #2 on the list), could rise to the top position. I suggest a "dummy" comparison between it and the actual #1 song, "The American Metaphysical Circus" (from 1968, by The U.S.A.) for discussional purposes.Instrumental originality
While both songs are absolutely brilliant and revolutionary, and both are severely multi-layered and vastly texturized and innovative, I personally believe an original use of instrumentation not only would be a stronger asset in Tomorrow Never Knows, but this song's very foundation. In this regard, The American Metaphysical Circus was highly experimental (employing some electronic devices, most notably a ring modulator, a calliope, strings and organ) but nowhere as original as Tomorrow Never Knows was if you consider each song's time of release as a context. In Tomorrow Never Knows, the Beatles used Indian instrumentation, which would soon become a staple of psychedelic rock, whereas the traditional rock instruments were used in absolutely groundbreaking forms (reversed guitar solos, sampled bass and drum patterns) thanks to the extensive use of tape loops (some of which even included mellotron recordings), exploiting and expanding upon how instruments could interact in a recording.Sound exploration
In my opinion, this one would go to Tomorrow Never Knows, again. I'm arguing for this song as the most important track in psychedelic rock's history, so better substantiate it. The song itself is a milestone, it marks a before and after division when it comes to sound exploration. The importance of tape loops is huge, its very use was an engineering landmark. Lennon's voice was outputted to a Leslie speaker, this was a first from Geoff Emerick, and many, many, bands would do this themselves later for vocal effects, The USA included. From Wikipedia: "Ken Townsend, the studio technical manager, created the first ADT system, taking the signal from the playback and recording heads and delaying them slightly." Yes, delay was introduced to rock music. This song marks the first use of voice double-tracking.http://en.wikipedia.org/wiki/Tomorrow_N ... #Recording
<- For reference.
The very impact of Tomorrow Never Knows' explorations are legendary, and, even as innovative as "Circus" was, its use of ring modulators and electronic devices was nowhere as influential as the former.Lyrical content
Tomorrow Never Knows was the blueprint for psychedelic mind-opening songs in 1966.
"Turn off your mind, relax and float down stream", "Lay down all thought, Surrender to the void", "That love is all and love is everyone", "But listen to the color of your dreams", etc.
The American Metaphysical Circus was a great poetical outing, in the same style as "For The Benefit Of Mr. Kite". Truly good, but not as influential.
"At precisely eight-o-five, Doctor Frederick von Meier, Will attempt his famous dive, Through a solid sheet of luminescent fire."Impact
& lasting influence
Tomorrow Never Knows was a smashing hit, whereas The American Metaphysical Circus introduced electronic instrumentation to rock's expanding sound. For short-term impact, both were good, but I think "Circus" was one of the latter masterpieces in psychedelic music, whereas "Tomorrow" was a milestone, starting point and peak. There goes influence. "Revolver" is today considered one of the greatest albums of all time, whereas The USA's debut album is considered a masterpiece as a whole, yet, for Revolver, most critics note how important "Tomorrow Never Knows" is. The song practically started psychedelic rock as a massive, viable movement, and only Sgt. Pepper's as an album would have as much influence and make an impact as strong as this one song.
And there's my 2 cents.