consider a sine wave of frequency x and in each cycle it has two portions that is the postive and negative side and consider that each one can carry a one bit information then each cycle can carry two bits. ie a x cycles can carry 2x bits so if the analog bandwidth is x then the digital bandwidth is 2x.
bandwidth is applicable only for analog
whereas baud rate and bit rate is applicable for digital.for instance,think about a gated room.at a number of persons can pass through the gate without jostling as well as wastage of space can be termed as bandwidth of gate.Towing same line, the capacity of signal to accomdate various frequencies is called as bandwidth
for a given circuit:
Analog Bandwidth is the usable range of frequencies for the circuit, that is the difference between the upper cutoff frequency and the lower cutoff frequency of the circuit.
Digital Bandwidth is the maximun number of digital uint the curcuit can handle in a unit time. It's call throughput.