in band on channel (HD radio) (IBOC)
In Band On Channel (IBOC), competing with DigitalAudio Broadcast( DAB), is the US base technology for HD radio. The difference to Digital Audio Broadcast lies in the channel processing.
The IBOC system broadcasts in the existing FM broadcast frequencies and transmits a digital carrier signal in addition to the analog, frequency-modulated FM broadcast signal. Both signals, the analog and the digital, are transmitted on the same carrier frequency. The advantage is that the transmitting equipment only needs to be slightly modified. IBOC uses Perceptual Audio Coding( PAC) for audio compression.
Because IBOC did not comply with the specified bandwidths in the U.S. and interfered with other broadcasting stations, it was shut down several times regionally.