still more about telephone bandwidth

[blazenka@public.srce.hr]

The analog telephone systems, bandwidth in Europe was 300 - 3400 Hz, but
nowadays all the voice communication is digitized. In Europe, the basic
sampling rate is once every 125 microseconds, which is 8000 times per
second. According to Information theory, the highest frequency in the
spectrum of regenerated signal could be half of the sampling frequency, that
is 4kHz.

If you are still interested I will look up the references for US and Europe.

Branko Sinkovic