Although his two ’60s albums are excellent, Peter Walker put his raga-like rhythmic strategies and stringent modalism to good use framing the fraught, terse lyrics he wrote for his 1970 Has Anybody Seen Our Freedoms? After Nashville’s Delmore Recording Society issued the long-lost Freedoms earlier this year, I caught Walker at a Music City show that demonstrated the guitarist’s pedagogical side — each song was a performance in a different key. It was a master class in improvisation, while Freedoms stands as a document of doomed American idealism. Meanwhile, a new generation of solo-guitar aficionados has begun to appreciate Walker’s abstract approach to composition. Also playing a set Friday night is Nashville’s William Tyler, an unclassifiable guitarist whose compositions use melodic themes that evoke everyone from The Byrds to Judee Sill. They’ll be recording their performances live to tape, for future vinyl release.