Interactive demonstration: bit rate equals signal rate times log2 of the number of levels; payloads from Forouzan's worked examples show what each bit rate can actually carry.

Bit rate = how often you change × how much each change says

Pick the levels L and the signal rate (changes per second). The bit rate follows.
YOUR SIGNAL
Each change carries log₂(L) bits: 1, 2, 3 or 4.
Changes per second. Physics (bandwidth) limits this — next lectures.
WHAT WOULD YOU LIKE TO SEND?
Where the number comes from
Required bit rate
Your bit rate
1 MB at your rate8,388,608 bits