Total posts : 45366
The receiver audio response curves displayed by Rich are very telling. In fact, those curves are the target for AM stations to serve.
None of them is exactly flat within its range, they are all mid-range emphasized, with the blue (average receiver) being the closest to flat.
The green has a little perk in the higher mid-range, a kind of self-post-emphasis.
But guess what, by using EQ (equalization) it would be possible to make a complementary curve so as to provide a flat response within the available range.
And guess what again. The AMT3000 and AMT5000 transmitters already anticipate the situation by providing a user selectable NRSC Pre-Emphasis which adds a 9.5dB treble boost to the top end.