Somerville, MA-based music site The Echo Nest has raised an undisclosed first round led by Commonwealth Capital Ventures with participation from angels. The Echo Nest offers what it calls “the musical brain” that synthesizes music information, analyzing what bloggers have said about a given song, its tempo, harmonic structure and other characteristics. The company, founded by two PhD students at the MIT Media Lab, also released development tools for other sites to incorporate the Echo Nest platform into their content. Release (pdf).