What is the Difference between Bit Rate and Baud Rate?

The difference between the two is complicated and intertwining. They are dependent and inter-related. But the simplest explanation is that a Bit Rate is how many data bits are transmitted per second. A baud Rate is the measurement of the number of times per second a signal in a communications channel changes.

Bit rates measure of the number of data bits (that's 0's and 1's) transmitted in one second in a communication channel. A figure of 2400 bits per second means 2400 zeros or ones can be transmitted in one second, hence the abbreviation "bps". Individual characters (for example letters or numbers) which are also referred to as bytes are composed of several bits.

A baud rate, by definition, means the number of times a signal in a communications channel changes state or varies. For example, a 2400 baud rate means that the channel can change states up to 2400 times per second. The term "change state", means that it can change from 0 to 1 or from 1 to 0 up to X (in this case, 2400) times per second. It also refers to the actual state of the connection, such as voltage, frequency or phase level).

The main difference of the two is that one change of state can transmit one bit - or slightly more or less than one bit, that depends on the modulation technique used. So the bit bate (bps) and baud rate (baud per second) have this connection:

bps = baud per second x the number of bit per baud

The number of bit per baud is determined by the modulation technique. Here are two examples:

When FSK ("Frequency Shift Keying", a transmission technique) is used, each baud transmits one bit; only one change in state is required to send a bit. Thus, the modem's bps rate is equal to the baud rate: When we use a baud rate of 2400, you use a modulation technique called phase modulation that transmits four bits per baud. So:

2400 baud x 4 bits per baud = 9600 bps

Such modems are capable of 9600 bps operation.