The second-to-last song on Dorothy Ashby's (probably) best album, The Rubaiyat of Dorothy Ashby.
Wonderful as it is, for the most part the album has very few surprises; say to someone that you've got an afro-groove-jazz-pop-psych harp-centric album inspired by The Rubaiyat of Omar Khayyam, and they'll probably imagine essentially the album as it actually is, all the more so if the person is already familiar with Ashby's late-period albums.
One surprising thing (not that music has to be surprising) is that the album is, as far as I can tell, unique in Ashby's catalog for having vocals. I actually am not sure if they're by Ashby herself--I think so--but regardless, they're wonderful. They occupy a kind of middle ground between the style you usually hear singing songs so sentimental they have the word sentimental in their title, and the style of singers such as June Tyson in her work with Sun Ra (by the way, I didn't know the song at that link until I searched youtube for June Tyson to find a quick example, and wow). On this song they lean more towards the former (you can tell right off, with the peak on the word "soul" and the way she holds and releases the "l" in "invisible"), and if not for the surroundings, the lyrics, the subtle, stereo-panned echo, and the particular, peculiar but warm reverb, you might almost think the singing more showtunesy than anything else.
The big surprise on this song comes at the very end, when the production on the voice changes completely and suddenly--where before the sonic atmosphere was entirely 1970, all of a sudden the vocals hop to the other channel and seem beamed in from the 1920s or 1930s, with the tinny, canned feel peculiar to the singing human voice recorded in those decades--I think the singer even puts a little more warble into her performance, to match the popular style of that time--and it's just for one line. And not even all of it, because on top of this, as she holds the last note, a crescendo in her performance is exaggerated by the sudden laying-on of a quick burst of reverb-laden delay, staying in the vocals' new channel and then bleeding quickly back into the other, lending an almost futuristic feel to the very final moments of the song.
The upshot of all this is that I like it a lot.