Sixty Seven Kilohertz has developed a system for dynamic ad-supported music ? dynamic because the ads change and are served randomly rather than be tied to the front of a particular song. ?A user can download tracks for free and save them on a portable device such as a cell phone with MP3 player,? said SixtySeven Kilohertz President Marc Cohen in a statement Wednesday. ?New ads are regularly transmitted to the device, saved, and played at non-predictable times between tracks of the to free downloaded music. A user can listen to the same track many times and different ads each listening session.? Cohen cites a study which shows that ?people are buying less music and listening to it for longer??which means (if the trend is valid and continues) there is more long-term revenue in advertising-supported music as opposed to pay-per-download.