baud

Baud is the unit of symbol rate in telecommunications, defined as one signaling event (symbol) per second. The term is named after Émile Baudot, a French telegraphy pioneer. In essence, baud measures how often the signal can change state each second, not the amount of data carried in each change.

The data rate, measured in bits per second (bps), depends on how many bits are conveyed per symbol. If each symbol carries k bits, then the bit rate equals baud × k. For binary signaling (one bit per symbol), 2400 baud yields 2400 bps. If the modulation uses four bits per symbol (for example 16-QAM), the same 2400 baud would yield 9600 bps. Thus, higher-order modulation can increase data throughput without increasing the symbol rate.

In practice, baud is commonly used to describe the speed of serial links and modems. The relationship to net data throughput is affected by framing, error correction, and protocol overhead, which can reduce the usable data rate below the raw bit rate implied by the symbol rate. The unit baud is a non-SI unit; in strict SI terms, symbol rate can be expressed in s⁻¹, but the term baud remains common in many contexts.

See also: bit rate, symbol rate, modulation, serial communication.