IBOC is the abbreviation for "In-band, on-channel" digital broadcasting, which is also known as hybrid digital radio. It was developed by iBiquity Digital Corporation and can be used on AM and FM channels. Using IBOC, the existing analog signal is transmitted in addition to the AM or FM station digital signal. In essence the digital information is sent along with the AM or FM signal which avoids extra frequency assignments. It is the only FCC approved digital system. 

The expectations are that IBOC will provide FM quality sound for AM listeners, and CD quality for those using FM. Employment of IBOC allows an easy transition from analog to digital without channel changes and avoiding service disruption. It also opens a potential competition of FM stations for listeners as AM reception improves.

There are several ways to configure IBOC. Pre-correcting the transmitter's output signal is seen as the best way to compensate for distortions. Solid state amplifiers have the least amount of distortion, also referred to as out of channel garbage. 

The FCC also approved AM stations use of IBOC at night, with the thought that any interference created would be outweighed by the benefits. At this time though, it seems the interference is enough to cause the AM stations to not use IBOC at night.

There is a group who opposes the use of IBOC as it is their view that it does not replicate mobile and indoor analog coverage. This means that the formerly clear adjacent channels are often overridden by the IBOC signals. This supports the group's claim that IBOC can easily put an end to listening to AM radio. Using the IBOC method for AM causes an eight second delay, which can be quite annoying for sports events!