DoubleTwist's music player has proven to be a popular alternative to Android's built-in music app. Google Play reveals the app has so far accumulated between 10 million and 50 million installations. But seeing as it's a free download, DoubleTwist hasn't yet found a great way to monetize that success. Today that it's taking on a new approach with the introduction of a new feature called Magic Radio. Priced at $4 monthly, the premium radio service mixes tracks in your own library with, by DoubleTwist's count, a catalog of over 13 million songs. Selections you hear will be "uniquely tailored to your musical taste" according to the description, suggesting Magic Radio aims to take on bigger players in music discovery like Pandora, Slacker, and Spotify radio. In an attempt to sway you away from those big-time competitors, DoubleTwist is offering a seven day trial of the premium service. Just be sure to cancel the trial in a timely fashion if you're not a fan, lest you be automatically billed for a full month of magic.