What a difference a day makes. On Monday Ilan Volkov and the BBC Scottish Symphony Orchestra, usually such fireballs, ended their Prom concert with a performance of Beethoven’s Pastoral Symphony so dull that I’m surprised the players stayed awake. On Tuesday the orchestra returned reborn, primed for an ear-stretching programme of electro-acoustic adventures.

The winds’ ferocious glare in Edgard Varèse’s 54-year-old Déserts took some beating, even with the industrial bedlam of the stretches for magnetic tape jammed in between. But the night’s strangest sounds emerged from the Speakings, the final fruit of Jonathan Harvey’s imaginative stint as the orchestra’s composer in association. His goal was to conjure the Buddhist notion of original speech – speech purified into mantras fusing song, vowels and consonants.

Surely, never before have an orchestra and electronics spent 27 minutes melting separate notes into so many muted wails and smeared glissandi: eerie music with the inflections of speech, but not words. The disappointment was that the spiritual level proved elusive: only in the final section did the mantra chatter become calm enough to touch the listener’s soul. A singular work nonetheless, skilfully delivered by the BBCSSO and the sound projection team from the Paris sound laboratory IRCAM.

Messiaen’s late Concert à quatre could only appear old-fashioned by comparison. The chuntering group of soloists suggests a concerto grosso; wilting melodies, one lifted from the composer’s youth, arrive kissed by sugared harmonies; the usual birds cascade on piano and winds. No masterpiece, definitely. But characteristic; and the four soloists showed their mettle, especially cellist the Danjulo Ishizaka, emotionally resonant no matter how small the composer’s gestures.

Some of Ishizaka’s projection might have helped Alban Gerhardt the night before in Prokofiev’s clotted Symphony-Concerto for cello and orchestra. The perfect antidote for that baggy monster was Elliott Carter’s Soundings, a crystalline ten-minute exploration of acoustic space for small orchestra with spidery piano interruptions (Nicolas Hodges) and a mellifluous tuba solo.

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