Precious few popular music vaults have been more prolific and consistently rewarding than Bob Dylan's deep trove. Since the groundbreaking 1985 "Biograph" boxed set, Dylan and his archivists have delivered one revelatory release after another, and this year is no exception. "The Witmark Demos," part of the ongoing "Bootleg Series," offers the most intimate of Dylan encounters. It contains 47 songs (15 previously unreleased) recorded for his first two publishing companies and performed just by Dylan with his guitar and harmonica. Listening is like having a ringside seat for his evolution from wannabe Woody Guthrie troubadour to folk provocateur to sophisticated chronicler of human emotions. The casual nature of the sessions-Dylan coughs during "Blowin' in the Wind" and stops "Talking Bear Mountain Picnic Massacre Blues" to correct a lyric, for instance-only enriches the experience. Meanwhile, "The Original Mono Recordings" offers up his first eight albums in immediate, arresting form. The release recaptures a sonic immediacy as well as instrumental details less prevalent in the more spacious and spread-out stereo mixes. These were Dylan's legend-builders, and their new versions, alongside "The Witmark Demos," make those six years seem that much more improbable-and impressive.