"Unheard" is the last in the Warp20 series of releases, but its contents will already be familiar to those who shelled out for the Warp20 boxset and possibly thought they were getting 11 exclusives. Not so I'm afraid, but "Unheard" is certainly good enough to work as a stand-alone album - so I suppose it's only fair that these tracks see the full light of day, although I must admit that as an owner of the aforementioned boxset I do feel a bit cheated.
ANYWAY Warp20 "Unheard", of all of the label's 20th anniversary releases, probably best typifies the Warp sound. No unheard Aphex Twin sadly, but you do get a quite good new Boards of Canada track. It's a good bit noisier (relatively speaking!) than other Boards' stuff and I suspect the reason it's previously unreleased is because it didn't quite fit on any of their previous releases, rather than any concerns over quality. Other highlights are the IBC mix of Autechre's "Oval Moon" (easy listening by their standards), Elektroids' (aka Drexciya) "Bonus Circuit" and Seefeel's "As Link" (in fact this and the other Seefeel track on Warp20 (Chosen) have both made me want to revisit this group who, I think I probably wrongly overlooked at the time as: token shoegaze band signed to a dance label).
If you're an occasional - rather than an obsessive Warp fan - or if you're just looking for an introduction to the label, this is the one to buy.