competing U.S. standard, but has been stagnant since the 2010s. Compatible AM Digital (CAM‑D) for AM stations. Digital Audio Broadcasting (DAB), a.k.a. Eureka 147, is the most common standard in Europe. Digital Radio Mondiale (DRM‑30 and DRM+ configurations) was intended mostly for shortwave radio. By May 2018, iBiquity Digital Co. claimed its HD Radio technology was used by more than 3,500 individual services, mostly in the United States. This compares with more than 2,200 services operating with the DAB system. A 400 kHz wide channel is required for HD FM analog-digital hybrid transmission, making its adoption problematic outside of North America. In the United States, FM channels are spaced 200 kHz apart as opposed to 100 kHz elsewhere. Furthermore, long-standing FCC licensing practice, dating from when receivers had poor adjacent-channel selectivity, assigns stations in geographically overlapping or adjacent coverage areas to channels separated by (at least) 400 kHz. Thus most stations can transmit carefully designed digital signals on their adjacent channels without interfering with other local stations, and usually without co-channel interference with distant stations on those channels. Outside the U.S., the heavier spectral loading of the FM broadcast band makes IBoC systems like HD Radio less practical. The FCC has not indicated any intent to end analog radio broadcasting as it did with analog television, since it would not result in the recovery of any radio spectrum rights which could be sold. Thus, there is no deadline by which consumers must buy an HD receiver. Technique Digital information is transmitted using OFDM with an audio compression format called HDC (High-Definition Coding). HDC is a proprietary codec based upon, but incompatible with, the MPEG-4 standard HE-AAC. It uses a modified discrete cosine transform (MDCT) audio data compression algorithm. HD equipped stations pay a one-time licensing fee for converting their primary audio channel to iBiquity's HD Radio technology, and 3% of incremental net revenues for any additional digital subchannels. The cost of converting a radio station can run between $100,000 and $200,000. Receiver manufacturers who include HD Radio pay a royalty, which is the main reason it failed to be fully-adopted as a standard feature. If the primary digital signal (HD‑1) is lost the HD receiver will revert to the analog signal, thereby providing seamless operation between the newer and older transmission methods. The extra HD‑2 and HD‑3 streams do not have an analog simulcast; consequently, their sound will drop-out or