No doubt that the sudden interest in Thomas Knak's back catalog was prompted by his work on Björk's Vespertine, so it's to his credit that he had enough quality material in the vault to justify this ensuant follow-up. Although technically an eight-track collection consisting of Opiate's hard-to-find and vinyl-only releases dating from 1998 to 2001, While You Were Sleeping neither feels extraneous nor self-indulgent. In fact, this collection of miscellany frequently eclipses Knak's still-wonderful debut (Objects for an Ideal Home) for quiet beauty. Although populated by elegiac organ sounds, chiming keyboards, and the occasional foray into glitch, While You Were Sleeping's main thematic thread revolves around Knak's pre-occupation with plosive and sibilant percussion sounds. As with "1% in 2/3 Speed" (Björk's "Undo" in its original form and seemingly built around ticker tape samples) or "Srain" (a concert of clocks being wound), this collection is positively loaded with gentle clicks, clacks, and chatters, which stammer in perfect contrast to Knak's pointed, well-honed melodies.
AllMusic Review by Mark Pytlik