As a conclusion to my MP3 identification contest, I am posting the solution to round 4. It took a while, but it was finally identified as the track A Cheval from the Michel Waisvisz album Crackle, released 1978 on FMP. Just like Tolerance's album Anonym, it is one of the great and insanely rare albums on the famous Nurse With Wound list. Fortunately, Michel Waisvisz is still around and, after a long hiatus, is back to composing, performing, and bending circuits again. Anyway, here is his classic album Crackle in its entirety as MP3:
Instruments used are a Crackle synthesizer, a modified "Putney" VCS 3 (on "One For The Road"), a mouth organ (on "Berliner Neustadtlament"), and a (modified) springboard built by the late great Hugh Davies (on "Stradivarius"). You can read more about the Crackle box here, and even order it at STEIM (currently on backorder due to shortage of parts).