16 or 20 kbps, either way it ain't enough for anything remotely "high fidelity". But it's probably still an upgrade for listeners versus the usual sub-5 kHz audio they get in car listening on AM now.
People have shown that they think SiriusXM's sound quality is "great" so obviously most listeners haven't the slightest clue of what music should actually sound like, which may work to AM HD's advantage.
Having both SiriusXM and HD radio in my car, I don’t know what people are smoking, but SiriusXM sounds like crap compared to HD radio. The processing used by SiriusXM makes everything sound artificial and there doesn’t seem to be a utilization of stereo sound. HD on the other hand, sounds crystal clear with surround stereo sound in my JBL speakers. That is, for the few stations that do HD radio right (the best Near me seems to be a Hubbard owned station, KDKB HD-2, playing an oldies format that is also heard on 92.7 FM).