Re: Rockwell's 56K is vapor

Jeff Weisberg (jaw@Op.Net)
Wed, 2 Oct 1996 12:51:45 -0400

| By Shannon's law(?), a local caller (one A->D conversion) actually can
| push at most 28K through the pipe (1/2 the sampling rate). Slightly higher
| rates can be achieved if the analog device matches the sampling rate at
| the Central Office.

close....

it's Nyquist's law that says that a signal bandlimited to B
requires a sampling rate of 2B.
our sampling rate is 8kHz. ergo, our signal is limited to (a
theoretical maximum of) 4kHz.

Shannon's law tells us that the Capacity of our channel
(in bits/sec) is
C = B*log2(1 + SNR)

where our noise is (mostly) due to quantization (to 8 bits)

--jeff