Sounds like: A wash that builds up into a moment instead of fading after it.
A swelling wash that builds into a moment rather than decaying from it — approximated on hardware (without true reverse-reverb processing) via a long amplitude swell into a heavily reverberant, sustained tail.
Open this patch in the interactive PatchpadDigitone II's ALGO 3 gives three plain carriers (C, B2, B1) when the FM depth of A and B is off, so LEV (A) and LEV (B) are both 0. MIX -64 selects the X tap (C + B2), and DTUN, which offsets only the ratio of operators A and B2, detunes B2 against C so the two beat against each other. DTUN below 64 is a very slight detune; above 64 is heavier. heavier' threshold at 64, for a clearly audible width without becoming a chorus effect. The FX page's REV send is pushed very high (~60%); the reverb's own decay/size time is set on the pattern-wide Reverb screen, not per-track, so push that separately to a long tail for the full building-swell effect.
AMP PAGE 2's MODE must be ADSR (the default for SY machines) so the long ATK/full SUS swell on AMP PAGE 1 actually holds. Push the pattern-wide Reverb screen's own decay time long for the full building tail -- the per-track REV value here is only the send level.
Oscillator 1 + 2 detuned via Oscillator 2's FINE (±100 cents) give the audibly wide pair. Reverb is pushed very high on both TIME and LEVEL -- the reverb itself contributes most of the sense of a building swell here, since Summit has no reverse-reverb algorithm of its own.
Osc 1 and Osc 2 are BasicWaves with Morph at 50 (pure sawtooth): the Morph knob runs from a square (0) through a sawtooth (50) to a double sawtooth an octave up (100), Sym only changes the pulse width below 50, and Sub adds a sine an octave down (0 here). Osc 1 + 2 detuned ~22 cents apart via Osc 2's real click-hold fine-tune -- MiniFreak's genuine second oscillator, not an invented unison mode. Reverb Time and Amount are both pushed very high; the reverb itself contributes to the sense of a building swell here. Values are on MiniFreak's native 0-100 scale.
Typhon's own FX3 Large Reverb is a real onboard module and is genuinely capable here, pushed to a large SIZE and long FEED (decay) for the building tail; no external send is needed. TUNE 2 turned noticeably off-center from VCO1 gives the audible detune width. Typhon can only run FX3 as Delay OR Reverb, never both.
Both Envelope 1 (pre-wired to Filter 1) and Envelope 2 (pre-wired to Amp) share the same long Attack so the filter opens in step with the amp swell. Reverb TIME is pushed close to its ~90s maximum-feeling range and DRY/WET pushed very high -- the reverb itself contributes to the sense of a building swell here, since Hydrasynth has no reverse-reverb algorithm of its own.
None of these synths have a literal 'reverse reverb' algorithm — this approximates the effect with a long amp-envelope swell into a heavy reverb tail, timed so the peak lands on the downbeat. A DAW-based true reverse-reverb process remains more authentic if available downstream.