In-band On-channel

In-band on-channel (IBOC) is a hybrid method of transmitting digital radio and analog radio broadcast signals simultaneously on the same frequency.

By utilizing additional digital subcarriers or sidebands, digital information is "multiplexed" on an AM or FM analog signal, thus avoiding re-allocation of the broadcast bands. However, by putting RF energy outside of the normally-defined channel, interference to adjacent channel stations is increased when using digital sidebands.

IBOC does allow for multiple program channels, though this can entail taking some existing subcarriers off the air to make additional bandwidth available in the modulation baseband. On FM, this could eventually mean removing stereo. On AM, IBOC is incompatible with analog stereo, and any additional channels are limited to highly-compressed voice, such as traffic and weather. Eventually, stations can go from hybrid mode (both analog and digital) to all-digital, by eliminating the baseband monophonic audio.