Vinyl is enjoying a comeback; could it now be the turn of mono? On the evidence of this pack of six CDs (also available in vinyl), there may be a limited case for it where very early stereo is concerned. Engineers whose careers had been devoted to producing a clear sound-picture in mono were still learning how to handle stereo. The stereo of Coltrane’s 1960 classic, Giant Steps, with saxophone and piano on the left, bass and drums on the right and a hole in the middle, is a mess compared with the mono. Conversely, there’s not much to choose between the two versions of Bags & Trane, from 1961. Either way, the music’s good.