One of the first things you'll notice about any tight-knit group of professionals or hobbyists is a tendency for jargon: words get cut-off after the first syllable, short phrases get turned into acronyms, and some common components even get nicknames. This is good for the initiated who want to save their keyboard strokes, but it can quickly confuse the newbie who is just getting into DIY. So, for the newbies, I have assembled all of the acronyms and other jargon that gave me a hard time when I started surfing the message boards. AD/DA: Analog-to-Digital or Digital-to-Analog converter Converts an analog waveform into a digital signal, and vice-versa. Converters that only go one way are called ADCs (Analog-to-Digital) or DACs (Digital-to-Analog). BOM: Bill Of Materials A directory of all the electronic components required for a certain project, usually in a Microsoft Excel document. Cap: Capacitor DOA/op amp: Discrete Operational Amp A self-contained amplifier built from discreet components such as transistors, resistors, and diodes. DOA's makeup the basis for popular projects like the API and Twin Servo preamps. DI: Direct Input or Injection or Interface Takes an instrument signal and turns it into one suitable for a microphone preamp. DIY: Do It Yourself EQ: Equalizer FET: Field Effect Transistor A special transistor often used in high-performance audio designs and the gain control mechanism for the 1176 FET compressor. IC: Integrated Circuit A self-contained electronic circuit squished into one piece of semiconductor. HPF/LPF: High Pass Filter / Low Pass Filter LDC: Large Diaphragm Condenser microphone LED: Light Emitting Diode Omni: Microphone with an omni-directional pickup patter Opto: Optical compressor A type of compressor that employs photo-conductive and a LED to set the amount of compression. Perhaps the most well known of this kind is the Urei/Universal Audio LA-2A. PCB: Printed Circuit Board Pot: Potentiometer A variable resistor used to control volume, eq, compression, etc. Sometimes called a 'knob.' Pre/Mic pre: Microphone preamplifier Makes a microphone signal loud enough to interface with a line-level device. Sometimes does some cool, non-linear stuff, too. PSU: Power Supply Unit RU: Rack Unit The accepted unit for measuring the height of rack cases. 1RU=1.75? or 44.45mm. SDC: Small Diaphragm Condenser microphone Schemo: Schematic A diagram of a circuit using lines and symbols. Awfully handy if you know how to read them. SMC: Surface Mount Component An electronic component that is mounted on the surface of a printed circuit board. Trafo/Tranny/Iron: Transformer TRS: Tip/Ring/Sleeve connectors Standard audio connectors. Vari-: Variable-gain () compressor A catch-all term for compressors that do not fit in another category, such as VCA, FET, optical, etc. VCA: Voltage Controlled Amplifier An amp that varies its output according to a control voltage. The heart of most hardware compressors on the market today. XLR: Cannon X Latch Rubber connectors