The conceit behind the 2015 box The Singles is simple: collect all the songs Johnny Mathis originally released as singles while he was at Columbia. That is a long stretch of time -- it begins with 1956's "Wonderful! Wonderful!" and ends in 1981 with "Nothing Between Us But Love" -- and The Singles also covers ground not often heard on a Johnny Mathis collection, with a full 31 of its 87 tracks seeing their CD debut here. It should be noted that this doesn't mean The Singles contains every one of Mathis' hits. Anything originally appearing on an album is not here, which means a handful of charting hits are missing in action (the biggest among these is "Misty," the 1959 number 12 hit that's part of the Grammy Hall of Fame), and while they're missed, there's also something to be said for breaking Mathis' career down to 45s. For one, it's easy to trace trends within this confined setting. Mathis may not have chased fads -- a large part of his charm lay in how he embraced old-fashioned crooning at the height of rock & roll, yet seemed youthful -- but times invariably change, no matter how intently Mitch Miller tried to preserve the middle of the road in amber. Miller handed over the everyday production reins of Mathis to Al Ham as the '50s gave way to the '60s and there was a slow shift in Johnny's records, as he retained the syrupy gaze of Miller but also broadened his palette to encompass elements of widescreen drama but, just as often, he'd return to the velvet pop he pioneered with Miller. Mathis took a four-year hiatus in the middle of the '60s, riding out the peak of the British Invasion and Motown over at Mercury, then returned to a Miller-less Columbia in 1967, finding it a place amenable to appropriations of current pop trends. Mathis remained a crooner -- he didn't dress in paisley and pick up an acoustic guitar -- but he dabbled in modern production trends and sang songs by Gordon Lightfoot, Jimmy Webb, and Burt Bacharach & Hal David. This stretch of singles -- beginning about halfway through the third disc and ending partway through the fourth -- is the most varied portion of The Singles, so it's the most interesting to hear, while the remaining late-'70s material is nice adult contemporary. Nevertheless, the first two discs contain the music that crystallized Johnny Mathis' appeal: he made the middle of the road seem fresh and if Mitch Miller's productions grow wearisome, Mathis' voice never does.