The portfolio includes seven music jukebox channels, mostly born from Emap brands, including The Box, Smash Hits, Q, Kiss, Kerrang, Magic and The Hits.
The broadcasters will use the joint-venture to "exploit new and emerging digital growth opportunities", with "increased cross-promotional opportunities spanning both media companies' portfolios'".
Channel 4 is preparing to launch three new digital radio stations next year and has also been mulling the launch of a dedicated TV channel under the 4Music brand following the success of its 'E4 Music' strand.
C4 chief exec Andy Duncan described the move as a "strategic investment... designed to generate significant revenues that can be reinvested in supporting our public service activity longer term".
Paul Keenan, chief executive of Emap consumer, added: "Emap and Channel 4 are likeminded partners and together we make a formidable force in an otherwise fragmenting and challenging market."
