Boston released “Dear Summer: Volume 1” last year – its first official summer mixtape and the country's only city-sponsored one. From hip-hop to rock to jazz, the new platform showcased the talents of local musicians and Boston’s rich musical heritage and legacy. Now “Dear Summer: Volume 2” is live featuring a new set of artists: six DJs and 17 artists (6-1-7, get it?) from the Greater Boston area for a 2-hour-long soundscape. This second annual collaboration has two aims: to “connect residents across neighborhoods through music, and to celebrate summer.” We speak with the mixtape’s co-producers to learn about this year’s edition.