Singer Myles Kennedy and guitarist Mark Tremonti recently began the songwriting process for ALTER BRIDGE's fourth studio album.According to ALTER BRIDGE bassist Brian Marshall, the band "is about eight songs deep in writing! There's some pretty heavy, cerebral stuff going on and it sounds awesome." The group plans to write and record over the next few months, with the record due to be completed before a planned September tour. ALTER BRIDGE's last studio offering, "AB III", came out in 2010 and included the hits "Isolation" and "Ghost Of Days Gone By". As previously reported, ALTER BRIDGE plans to release a new box set on May 14, according to a message posted by the group at its website. The band has also launched a separate site for the package itself, although all that features at the moment is a countdown clock and a video teaser trailer. There's no word on what the box set will contain, although it will likely include the band's three previous studio discs or at least selections from them, along with a live disc released in 2011. During ALTER BRIDGE's break, Tremonti recorded his first solo album, "All I Was", and toured behind it, while Kennedy recorded all the vocals for Slash's second solo effort, "Apocalyptic Love", and toured the world as part of his live band. Tremonti, Marshall and ALTER BRIDGE drummer Scott Phillips have also toured as part of their original act, CREED, who have also been working on new material.