For digital radio, the FCC chose proprietary HD Radio, which crowds the existing FM broadcast band and even AM broadcast band with in-band adjacent-channel sidebands, which create noise in other stations. This is in contrast to worldwide DAB, which uses unused TV channels in the VHF band III range. This too has patent fees, while DAB does not. While there has been some effort by iBiquity to lower them, the fees for HD Radio are still an enormous expense when converting each station, and this fee structure presents a potentially high cost barrier to entry for community radio and other non-commercial educational stations when entering the HD Radio market. (Under the subsidiary communications authority principle, FM stations could in theory use any in-band on-channel digital system of their choosing; a competing service, FMeXtra, briefly gained some traction in the early 21st century but has since been discontinued.)