KNOW THE LINGO — WHAT IS BAUD?
By: Joseph D. Cornwall, CTS-D
Technology Evangelist — C2G
Technical lingo is a kind of shorthand that's used to express concepts common to that specific topic or area of study. Technical lingo is important because it provides a very precise or unique "shorthand" description of a device, effect or concept. Unfortunately, if you aren't comfortable and familiar with the lingo of a topic it can be a tall hurdle to communicate efficiently with folks who consider the jargon of their field to be "self-explanatory." In this series of articles we'll lift the veils of misunderstanding from the lingo of the A/V industry.
WHAT IS BAUD?
Years ago (for those of us who've been in the industry since compact disc was an emerging idea) we used to speak of modem speed in "baud rate." It's rare to hear that unit used outside of serious engineering circles today, but it is still an important concept. While we may have lost the word "baud" from the casual lexicon (when was the last time you discussed a 14.4 baud modem?) once we moved beyond 20th Century icons like Prodigy, AOL and Compuserve, we certainly haven't lost the need to understand data transfer rates over an analog connection. The concept of baud will make an important comeback when we discuss HDBaseT and other new digital video transfer systems.
Baud is similar to the gross bit rate of data transfer we typically express in bits-per-second (bps). For example, you might say one that the IT network in your building is delivering one gigabits per second (Gbps). You wouldn't say that the network is operating at one gigabaud, however. To understand the difference we need to take a look at history.
The baud was named for Jean-Maurice-Emile Baudot, a 19th Century engineer and inventor. Baudot worked during a time when Morse Code was state of the art. He managed to invent a system that allowed multiple transmissions to take place simultaneously over a single line. This early teletype system made it possible for multiple text messages to be sent over a single telephone line. This revolution in transmission made possible the connection of distant cities over a single cable, and thus began a journey that ultimately produced the Internet.
The baud is the unit of symbol rate or modulation rate, which is the number of distinct changes made to the transmission medium per second in a digitally modulated signal or a line code. In "pure" digital systems (i.e., using discrete/discontinuous values) with binary code, 1 Bd = 1 bit/s. But since it really isn't possible to send "1's and 0's", in practice we typically represent this digital value by using analog levels. The signal inside the wire is analog and it represents digital data. Analog connections use a continuous range of values to represent information, and in these systems the exact informational size of one Bd varies. Typically the data rate (bits per second) is significantly larger than the symbol rate (baud rate) because a single symbol can represent more than one bit.
Because baud is the rate of changes made to a carrier wave each second, it has a direct relationship to frequency bandwidth as measured in hertz. This is why category cables have their bandwidth specified in megahertz (MHz, or millions of cycles per second) and not Mbit/s and it begins to point us to the explanation of why a Cat5e cable, specified at 100MHz bandwidth, can make a Gigabit connection.