Ballard, 24, spent the last two seasons with the New York Giants after originally entering the NFL as a rookie free agent out of Ohio State in 2010. He was released by the Giants on June 11, 2012.
After spending his first season rotating between the practice squad and the active roster for the Giants, the 6-foot-6, 275-pounder played in 14 games with 13 starts in the regular season last year and caught 38 passes for 604 yards and four touchdowns. He played in all four postseason games, including Super Bowl XLVI against the Patriots, and finished with five receptions for 43 yards. Ballard caught two passes for 10 yards in the Super Bowl.
Herman, 22, joined the Patriots as a rookie free agent on May 10, 2012. The 6-foot-5, 255-pounder, played in 12 games with three starts as a senior at Iowa last year, finishing with eight catches for 95 yards and two touchdowns.