My interpretation of the sentence is that digital radio is truly digital, and that "in conjunction with their analog signals" means "in conjunction with their legacy AM/FM signals." The sentence isn't clear, clearly. They are likely using a single transmitter for all of the signals, with all signals being in a narrow band around their legacy signal. But I haven't seen a real engineer's description of the signal content anywhere. I can (or once could) give you the full math for AM and FM signals -- learned about it in college engineering in the '50s. I have no idea how actual digital signals work, other that a general understanding of digital sampling. One could take the digital audio from an MP3 (or other digital audio format) and transmit it digitally, with the digital to analog conversion occurring in the receiver. I think that's likely what they are doing.
The following from the later portion of the earlier-cited Wikipedia article: "If digital signal reception is lost, the HD Radio receiver will revert to the analog signal, thereby providing seamless operation between the newer and older transmission methods-ONLY for the primary HD(-1) signal (The extra HD-2 and HD-3 streams are not simulcast on analog, thus are totally lost when digital reception is gone). Alternatively the HD Radio signal can revert to a more-robust ~20 kilobit per second stream, provided the broadcaster has that setup as well. Datacasting is also possible, with metadata providing song titles or artist information." would seem to indicate that the primary (HD-1) channel's audio is broadcast digitally as a copy of the legacy (POFM) channel, and the HD-2 and HD-3 channels are broadcast with different audio content only in digital mode. "iBiquity Digital claims that the system approaches CD quality sound and offers reduction of both interference and static;[9] however, some listeners have complained of increased interference on the AM band (see AM, below)." Fred Holmes At 06:55 AM 2/7/2010, Mike Sloane wrote: >Read the sentence again: the audio is still analog, but there is a digital >data stream along with it that is used for station ID/playlist/etc. >information. This is different from digital TV, where the entire signal is >digital. > >Mike > >Art Clemons wrote: >>>I think you are under a misunderstanding. HD radio is NOT "digital". It is a >>>proprietary format analog signal with a digital adjunct. See: >>><http://en.wikipedia.org/wiki/HD_Radio> >>Both IBOC signals are truly digital although on AM, it's a Hybrid Digital >>system. Please note that your quoted source to rebut the claim that HD is >>digital states: >>"HD Radio is the trademark for iBiquity's in-band on-channel (IBOC) digital >>radio technology used by AM and FM radio stations to transmit audio and data >>via a digital signal in conjunction with their analog signals.' ************************************************************************* ** List info, subscription management, list rules, archives, privacy ** ** policy, calmness, a member map, and more at http://www.cguys.org/ ** *************************************************************************
