The HD radio is a hybrid digital radio.. It receives AM, FM, and HD signals. It received both analog and digital signals. The AM digital sounds more like the present FM and the FM is more like a CD sound. The HD sound is pure digital and the sound is great. If there is any type of defect in a CD playing, it will be recognized immediately.

Few people are familiar with the HD radio today but the radio broadcast stations are rapidly changing to the HD format. The hardware cost is still very high compared to a normal AM/FM radio. The cost varies from $100.00 to $600.00 and up. I would expect the cost to be greatly reduced when these are in mass production.

The broadcast stations love this format because they can get many more stations broadcasting on the same bandwidth. The signals are bundled together and compressed. The AM and FM analog signal bundled with the digital signals of AM, FM, HD1 and HD2 etc. The digital signals are compressed. The new HD radio will simply receive the signal for the radio settings. If the digital AM is playing and it looses its digital signal, it will simply revert to the AM analog signal.

The government has forced Television stations to broadcast in all digital in the near future. Customers with the old analog TV's will be required to either buy a new digital TV or obtain a set top box to convert the digital signal back to analog. The government is not forcing this on radio but they are proceeding on their own because this is the greatest improvement in radio sound since the introduction of FM years ago.

The patent for HD technology is held by iBiquity Digital Corp. and all stations will pay a royalty fee for the technology. I do not know what this license fee is but it is not holding back the development of this new sound. Few people are familiar with this technology but they will be hearing a lot about this in the next few months.

Will the public cancel their satellite subscriptions and turn off their MP3's and iphones etc for this new sound? This should go with lightening speed when the prices fall and we have hand held and pocket radios. Now they are only available in table top designs and automobile installations. This is all I have seen.

The NPR stations and stations in larger and medium size cities are changing fast so that by 2008 I would expect many stations broadcasting in HD format. The critics say that it has not been proven and the technology may not work. Supporters say that by improving the sound to digital, everyone wins. The technology has been proven by now and we will see the improvements in our homes soon. The United states and the world is in the middle of the digital revolution and digital radio is simply a small part of it.