c=2*bandwidth????

please help me!
i want to know that how the formula for maximum channal capacity ( bits per seconds) is derived.

c= max. channel capacity
b= bandwidth
v= no.of dicrete levels

for noise less channel we know
c= 2b(loghaving base 2)v

for binary system v=2
thus c= 2b
means if channelbandwidth is 3000 hz ,then channal capacity is 6000bits/sec.
how???