Radium wrote:
....

You miss the simple point, the dc is the carrier ... instead of dc, you
could put a 1 hz signal on the line and modulate it with your voice,
indeed, you can put a 30 hz signal on the line and modulate it with your
voice--if you can tollerate a bad 30 hz hum! But, who knows, perhaps
you are tone deaf to the 30 hz hum and would like it ...

JS