This is an application of the Lexicon MPX-1 5th-Octaverb preset, running in the suboctave mode.  The melody is generated by the Blacet Binary Zone driving two MOTM-300 VCOs with the Modcan Dual Quantizer in the middle.  Some randomness hits the quantizer transpose CV input.   The notes are gated by envelopes triggered by the pulse outputs of the quantizers, which yield a pulse whenever a note changes.  MOTM-440 and MOTM-480 filters are included.