What’s the difference? While both HD AM and HD FM are digital, AM radio has smaller sections of bandwidth than FM radio. This means there is not enough "space" to give AM stations the same near-CD quality as FM stations. But there is enough bandwidth that AM stations will be able to broadcast with the same clarity of signal as one of today’s analog FM stations. This performance boost is expected to make AM radio a better alternative to FM than it has been – to give you more listening choices.
Because HD radio is digital, its signals can be subdivided. This allows a station to multi-cast. meaning it could broadcast two or more programs at the same time. So, its listeners might be able to choose between music from the ’60s, ‘70s or ‘80s – on the same station at the same time.
This could change everything you know about radio because it allows stations to do more niche broadcasting, just as cable as brought niche channels to television. For example, the radio station you’ve always tuned to for classic rock, might subdivide into classic rock, and reggae, or classic rock and old school hip-hop.
Naturally, you would be able to hear these stations only if you have an HD receiver. If you don't, you'll still hear the same AM or FM station you're used to.
