It isn't a 56kHz channel. It is a 56k bps channel encoded as complex tones onto a 4kHz voice connection. The telephone system wiring does not have the bandwidt

It isn't a 56kHz channel. It is a 56k bps channel encoded as complex tones onto a 4kHz voice connection. The telephone system wiring does not have the bandwidth to carry a signal that is 2-3x the range of human hearing.