Pandora Media will increase fees for its ad-free music-streaming service by $1 a month to almost $5 a month in May to cover the rising cost of licensing tunes. The company, which streams music from virtual radio stations to mobile devices such as Apple's iPhone or Google Android smartphones, said in a Tuesday blog post that royalties paid to artists had risen 53 percent over the past five years and will rise another 9 percent in 2015. The increase of $1 to $4.99 a month takes effect for new subscribers in May. Existing monthly subscribers will not be forced to accept the higher charges for now, the company said without elaborating. Annual subscriptions will be discontinued while early subscribers currently paying $36 a year will move to a monthly, "loyalty" $3.99 plan once their memberships expire.