Former Grateful Dead drummer Mickey Hart has been touring since last fall with a red-hot new band and a batch of excellent songs he co-wrote with the Dead’s lyricist, Robert Hunter. The Mickey Hart Band is finishing up their first album, Mysterium Tremendum, at Hart’s home studio in rural Sonoma County, Calif., co-producing the CD with Ben Yonas, who also engineered (and plays keys in the band). This group is more song-oriented than some of Hart’s previous outfits (it boasts two fine singers, Tim Hockenberry and Crystal Monee Hall), but there are still giant grooves and plenty of sonic weirdness from Hart, including sounds from actual astrophysical phenomena, from quasars to the Big Bang. “We recorded almost all the basics in four days,” Hart says. “I’ve never done a record that fast; that’s light speed for me!” The album is due April 10.