Baud

:For the town in France, see Baud, Morbihan.

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In telecommunications and electronics, baud (pronounced ) is a measure of the "signaling rate" which is the number of changes to the transmission media per second in a modulated signal. It is named after ?mile Baudot, the inventor of the Baudot code for telegraphy.

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For Example: 250 baud means that 250 signals are transmitted in one second. If each signal carries 4 bits of information then in each second 1000 bits are transmitted. This is abbreviated as 1000 bit/s.

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Note : Baud rate should not be confused with data rate (also called "bits per second").

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Each signalling event transmitted can carry one or more bits (as many as 256 in 256-QAM modulation) of information. When each signalling event transmitted carries one bit the baud rate and the data rate are equal. However, it is more common to make better use of bandwidth by encoding multiple bits in one event. This reduces the transmission time required for sending information.

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Thus, a 2400 bit/s modem actually transmits at 600 baud, where each quadrature amplitude modulation event carries four bits of information.

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A clear example of the difference between the baud rate (or signalling rate) and the data rate (or bit rate) is a man using a single semaphore flag. He can move his arm to a new position once each second, so his signalling rate (or baud rate) is 1 per second. However, the flag can be held in one of eight distinct positions: Straight up, 45 degrees left, 90 degrees left, 135 degrees left, straight down, 135 degrees right, 90 degrees right, and 45 degrees right. This means each signal carries three bits of information, as it takes 3 binary digits to encode 8 distinct states - so the data rate is 3 bits per second.

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Modems work in the same way - a 2400 bit/second modem will typically have a baud rate of 600 per second - but each signal carries 4 bits of information encoded within it, allowing a data rate of 2400 bits/second.

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