Aaron is bound to jump in here to correct what I am about to say, but if you disregard some seldom (if ever) used features of the system, my understanding is that you've basically got 96 kbps to play with. You can allocate this in a variety of ways, but the most common is: if only HD(1), all 96 goes to HD(1), if you also have HD-2, you are most likey to allocate 48 kbps each to HD(1) and HD-2 (although some stations may use 64 kbps for HD(1) and 32 kbps for HD-2). If you have HD(1), HD-2, and HD-3, you are most likely to allocate 32 kbps to each. I believe that 32 kbps is all that's available in the AM-band system. Maybe someone can explain why 32 kbps sounds better on an FM-band HD subchannel than it does on the AM-band system, but I know of no reason why it should sound any different. Even if they can't tell the difference between 96 kbps and 64 kbps, I would think a lot of people ought to be able to tell the difference between 96 kbps and 32 kbps.