Sounds like: A sustained bass that slowly says 'ah-oh' as the filter moves.
A sustained bass note where a slow filter movement creates a vowel-like 'ah-oh' quality — the note itself barely changes, the formant-style filter sweep is the whole performance.
Open this patch in the interactive PatchpadDigitone II's filter is a lowpass/bandpass/highpass morph, not a true fixed-peak bandpass — Resonance pushed high (RESO 70) on FLTR page 1 stands in for the vowel-like peak. MOD page 1's LFO drives FLTR Freq directly at a slow rate for one sweep roughly every 3-5 seconds; SPD 18 with MODE FREE runs unsynced against a held note for the 'ah-oh' movement.
Syntakt's filter has no true bandpass mode on the melodic Digital-machine tracks, so high Resonance on a lowpass stands in for the vowel-like peak. LFO PAGE 1 drives FLTR Freq at a slow rate for the vowel sweep. AMP PAGE 2's MODE must be ADSR (the default for SY machines, but drum machines default to AHD), or SUS on AMP PAGE 1 is ignored and the held note can't sustain.
Summit's true bandpass FILTER SHAPE gives a noticeably more convincing vowel than lowpass-with-resonance. LFO 1 is filter-dedicated on Summit (its Depth knob lives right on the FILTER page), so no Mod Matrix routing is needed — a genuinely simpler signal path than the other synths here. Live control: the Mod Wheel speeds up LFO 1 through Mod Matrix slot 1 for the talking speed.
Osc 1 is Formant: Wave sets the interval between the two formants, Timbre the base formant frequency (the vowel position) and Shape the formant width. LFO 1 runs a Tri wave at 1.5 Hz. Mod Matrix: the LFO 1 row to the Cutoff column at +35. ENV/VELO is 0 so the Envelope leaves Cutoff alone; LFO1 via the Modulation Matrix drives the slow vowel sweep instead. Macros: M1: LFO1 Rate, for live-performable talking speed. Values are on MiniFreak's native 0-100 scale.
Typhon's own filter is a low-pass only. M1 (one of Typhon's three real modulator slots) is set to MODE LFO with DEST CUT, giving a genuine tempo-independent sweep — a real routed modulator, not just a front-panel knob position. FX1 includes a resonant 2-pole high-pass filter (its CUTOFF, 20 Hz to 20 kHz, in series after the VCA), so Typhon's low-pass plus that high-pass in series forms a band-pass: close CUTOFF partway and raise FX1's high-pass to narrow the band around the vowel-like peak.
Filter 1's real Vowel type is a genuine vocal-formant filter mode, a more literal match than the resonance-pushed-lowpass workaround the purely-analog synths need. LFO 1 is pre-wired to Filter 1 (its own LFO 1 AMOUNT knob), so no Mod Matrix routing is needed for the sweep itself.
A true bandpass filter (rather than lowpass-with-resonance) gives a much more convincing vowel effect where available — worth checking each synth's filter mode options.