What exactly is London/Decca

I'm hoping someone may enlighten me on what exactly a London/Decca "Phase 4" record is. At first, I thought it must be a quadraphonic record, but I've picked up a few and they aren't. Most seem to be from the late 60's. One came with a promotional insert that describes it as a "marvel of sound" (not particularly enlightening). Might anyone know what the difference is between a "Phase 4" London/Decca and any other non-Phase 4 London/Decca record? Tks.

The "Phase 4" recordings were a departure from the
normal recording techniques applied by Decca. They are
highly multi-miked, and closely miked to maximize impact of
the instrumental sounds. No attempt is made to create a
natural soundstage, as in the classic miking techniques from
the standard music catalog.

The *London* Phase 4 recordings are different in tonal
balance from the *Decca* Phase 4 recordings. Unlike the
standard catalog, the Phase 4 catalog was separately
mastered for the U.S. market, boosting bass and treble. The
Decca Phase 4 pressings mastered for the British domestic
market, while still multi-miked and closely miked, were
mastered with a more neutral tonal balance.

Some Phase 4 recordings can be very impactful, dynamic and
exciting. But, don't go to this sub-label for natural
sounding recordings that attempt to faithfully capture the
music event from an audience member's perspective. Consider
the Phase 4 catalog a fun and frivolous adventure in sound
for sound's sake.

Some Phase 4 recordings for classical music fans to seek

- Stokowski / Scheherazade
- Munch / Pines of Rome
- Herrman / any of his own works that he conducts
Rushton is quite right in his explanation of Phase 4 recordings. I have been purchasing a few of these lately, and to me they are more thrilling to listen to than SACD Classical recordings. Some of the ones I particularly am enjoying is Stanley Black/Beyond The Sea, Ronnie Aldrich's twin piano recordings, and several from Werner Mueller. Some of the stuff is kinda wild and different. Try some and enjoy!
Rushton - thanks so much for your fulsome response. I'm a classical enthusiast who is new to vinyl, so I'm fascinated about learning more about the classical labels, their histories, technical merits, etc. Have you found anything on the web or elsewhere that you have found insightful or interesting on this subject? Thanks again.