According to DIN 44302, the step rate is the reciprocal of the shortest nominal time span, the step duration, between successive significant time points of a modulated signal. If the time span is expressed in seconds, the unit of measurement is the baud. The step rate determines the frequency band occupied during transmission and is generally lower than the transmission rate.
The step rate or symbol rate thus indicates the maximum number of information units that can be transmitted over a channel in one second. The range of values of the signals can be different, depending on the valence of the signal: bivalent or binary, trivalent or ternary, tetravalent or quaternary, and so on. This value range varies according to the characters to be transmitted with each signal and can be realized by one or more fixed physical parameters such as current, voltage, frequency or phase angle.