Electrical Terms:

Algorithm: a set of mathematical "rules" applied to an input. Generally used to describe a section of computer code which performs a specific function

Allegro: A PCB Editor family name found in the Cadence OrCAD and Allegro families

Alternating Current (AC): A current whose polarity alternates from positive to negative over time. The rate of such "alternations" is measured in cycles per second - more commonly known as Hertz (Hz)

Amp / Ampere: The basic unit of current flow

Ampere Hour (Amp hour, Ah): a measurement of the capacity of a storage medium (a single cell or a battery). A cell which can supply 1 Amp for 1 hour before it is discharged to a specified minimum level is said to have a capacity of 1 Amp hour

Amplification: a method for increasing the amplitude (or loudness) of electrical signals

Amplifier: An electronic device which generates a high power signal based on the information supplied by a lower powered signal. A perfect amplifier would add or subtract nothing from the original except additional power - these have not been invented yet

Amplitude: the loudness of sound waves and electrical signals. Amplitude is measured in decibels (dB) or volts

Analogue to Digital Converter (ADC): A device that converts the infinite range of an analogue signal into discrete "steps". Normally, a good audio ADC will use sufficient "steps" to resolve the smallest musical detail. For CD, this is a 16 bit converter, having 65,536 discrete levels covering the most negative signal level to the most positive

Attenuation: the decrease of a signal's amplitude level over any distance during transmission or through purpose designed attenuators. Attenuation measures signal loss in decibels (dB)

Bandwidth: the measure of a range of frequencies containing an upper and lower limit

Battery: a bank of individual cells connected together to provide the required voltage

Binary: the basic counting system used in computer logic. Two values are available - 0 and 1. A zero is normally represented by a 0 Volt signal, and a one by a voltage of approximately 5 Volts - these levels are dependent upon the type of logic used

Binary Code: a coding scheme that communicates information by using a series of "1s" and "Os" that are represented, respectively, by the digital "ON" and "OFF" states

Bit Stream: the bit rate, or flow of information, between a sender and receiver in digital communication. Also called Digital Bit Stream.

Bit: a unit of the binary code that consists of either a single "1" or "O." (Commonly 5V or 0V respectively.)

Bus: a pathway that connects devices, enabling them to communicate. May be digital or analogue, including power and earth (ground).

Bypass (1): the practice of using (typically) low value capacitors to conduct high frequency signals either to earth or around an amplifying device. Ensures that power supplies remain low impedance up to very high frequencies to ensure that circuits remain stable.

Bypass (2): an arrangement commonly using switches or relays to route a signal around a piece of circuitry. Bypass switches are very common with effects units, whether designed for studio, live performance or individual musicians (guitar effects pedals for example).

Byte: a unit of the binary code that consists of eight bits. One byte is required to code an alphabetic or numeric character, using an eight-bit character set code.

Cable: a type of linear transmission medium. Some of the common types of cables include: hook up wire, coaxial (shielded) cables, lamp amd mains cable, figure-8 (zip) cable and fibre optics

Capacitor: A pair of parallel "plates" separated by an insulator (the dielectric). Stores an electric charge, and tends to pass higher frequencies more readily than low frequencies. Does not pass direct current, and acts as an insulator. Electrically it is the opposite to an inductor. Basic unit of measurement is the Farad, but is typically measured in micro-farads (µF = 1 x 10-6F) or nano-farads (nF - 1 x 10-9F).

Capture: is a schematic editor package found in the Cadence OrCAD and Allegro family products

Cell: one section of a battery. The common carbon or alkaline cells used in battery operated equipment, for example.

CMOS: (Complementary Metal Oxide Semiconductor) - one family of digital logic devices. Some CMOS devices can operate with power supplies from 3 Volts to 15 Volts - others are limited to the traditional logic 5 Volt power supply.

Coaxial Cable: a metallic cable constructed in such a way that the inner conductor is shielded from EMR (electromagnetic radiation) interference by the outer conductor. Coaxial cable is less susceptible to more transmission impairments than twisted pair cable, and it has a much greater bandwidth; thus coaxial cable is used by most analogue and digital systems for the transmission of low level signals.

CODEC: COder / DECoder - the component of any digital ssubsystem which performs analogue to digital and digital to analogue conversions.

Colour Code: used to identify resistors and some capacitors, as well as wires in telephony. For telephone cables, the basic colour code for the first group of pairs is Blue, Orange, Green, Brown, Slate (grey), with white "Mates". The Mate is the most positive lead, and is the Tip connection.

Compression (1): the component that joins together with a rarefaction to make a sound wave.

Compression (2): the act of compressing (making smaller) a digital data stream - e.g. converting from 16 bit signals to 8bit signals. Most compression schemes are "lossy", which is to say that some of the original data is discarded and cannot be reconstructed.

Compression (3): a circuit used to restrict the amplitude variations of a signal (often combined with a limiter to set an absolute limit). Unlike digital compression, analogue compression can be "undone" to restore the original signal with little degradation.

Crossover: A filter network which separates frequencies into "bands" which match the capabilities of the loudspeaker drivers within an enclosure.

Crosstalk: a noise impairment when a signal from one pair of wires affects adjacent wires or one channel affects the adjacent channel.

Cutoff Frequency: Normally defined as the frequency where the output from a filter has fallen by 3dB from the maximum level obtainable through the filter.

dB - Decibel - (0.1 Bel): defined (more or less) as the smallest variation of volume detectable by ear (under laboratory conditions). This is measured on a logarithmic scale, so a change of 3dB from 1 Watt is equivalent to 0.5 Watt or 2 Watts. A change of 10dB from 1 Watt is equivalent to 100mW or 10 Watts. In electronics, 0dBm is a reference value corresponding to 1mW at 600 Ohms - this equates to approximately 775mV. The threshold of sound is 0dB SPL, and typical sounds can reach 140dB SPL or more. Any prolonged sound above 90dB SPL may will cause hearing damage.

Digital/Analogue Conversion: a method used to recreate an analogue signal that has been coded into binary data and transmitted as a digital signal.

Digital/Analogue Converter (DAC): a device used to generate a replica of the original analogue signal that has been coded into binary data and transmitted as a digital signal.

Direct Current (DC): A current flow which is steady with time, and flows in one direction only.

Distortion (1): Any modification to a signal which results in the generation of frequencies which were not present in the original.

Distortion (2): Of phase, any modification of the phase relationship between two or more signals which causes the observed waveform to differ from the original.

DSP: Digital Signal Processor - a dedicated computer circuit which performs complex changes or analysis on a digital signal, generally encoded from an analogue source.

Electronic: The use of active electronic components (integrated circuits, transistors, valves etc) which require a power supply to function. Such "active" components will always be used in conjunction with passive components.

Earth (1): also known as ground - commonly used to describe the chassis and other materials that provide a return path for power supplies and signals within any electronic device.

Earth (2): also known as ground - a protective connection from wall outlet to equipment chassis to conduct fault currents away from human contact.

Electromagnetic Interference (EMI): an unwanted (possibly interfering) signal emitted by any electronic apparatus. The emission of EMI is heavily regulated in most countries.

Electromagnetic Radiation (EMR): a transmission medium that includes radio waves and light waves.

Farad: the base unit of capacitance - equal to the capacitance of a capacitor having an equal and opposite charge of 1 coulomb on each plate and a potential difference of 1 volt between the plates (Abbreviation - F). The Farad is a very large value, and is more commonly referred to as the pico-Farad (pF, 1 x 10-12 Farad), nano-Farad (nF, 1 x 10-9 Farad), micro-Farad (uF, 1 x 10-6 Farad), and (less common) milli-Farad (mF, 1 x 10-3 Farad).

Filter: a circuit which is frequency dependent. The "pass band" is the range of frequencies allowed through, and the "stop band" is that range of frequencies which are blocked.

Filtering: a process used to remove or accentuate specific frequencies or frequency ranges of a signal.

Frequency: The rate at which an alternating current changes in a cyclic manner from positive to negative and back again (one cycle). The basic unit of measurement is the Hertz (Hz), which equates to one cycle per second.

Frequency Modulation (FM): a modulation technique that records changes in an information signal by modifying the frequency of the carrier signal according to changes in the amplitude of the information signal.

Henry: The basic unit of inductance in which an induced electromotive force of one volt is produced when the current is varied at the rate of one ampere per second (Abbreviation - H).

High-pass: A filter which allows high frequencies to pass while blocking low frequencies.

Hertz (Hz): the measurement of frequency. Hertz represents the number of cycles of an electrical signal measured in one second.

Impedance: A load applied to an amplifier (or other source) which is not a pure resistance. This is to say that its loading characteristics are frequency dependent. Impedance consists of some value of resistance in conjunction with capacitance and/or inductance. The equivalent circuits can vary from two components to hundreds.

In-Phase: a condition of two waveforms when they cross the reference line at the same time and in the same direction.

Inductor: A coil of wire which exhibits a resistance to any change of amplitude or direction of current flow through itself. Inductance is inherent in any conductor, but is "concentrated" by winding into a coil. An inductor tends to pass low frequencies more readily than high frequencies. Electrically it is the opposite of a capacitor. Basic unit of measurement is the Henry (H), in crossover networks it will typically be measured in milli-henrys (mH = 1 x 10-3H) and for RF micro-henrys (µH) are common.

Insulator: A material that prevents the passage of electricity, heat or sound. The plastic coating on wires is an insulator, preventing the wires from coming into electrical contact with each other. Insulators are extensively used in electronics. Most good electrical insulators are also good thermal insulators.

Integrated Circuit (IC): A collection of active and passive devices (e.g. transistors and resistors) mounted on a single slice of silicon and packaged as a single component. Examples include operational amplifiers, Central Processing Units (CPUs), random access memory (RAM), etc.

Intermodulation Distortion (IMD): the intermixing of two frequencies. It is often caused by non-linear distortion within an amplifier or loudspeaker system.

Laser: Light Amplification by Stimulated Emission of Radiation. Originally, lasers were either gas or precious stone (e.g. ruby), but are now made using semiconductors. Laser light is coherent, meaning that the emitted light waves are in phase, which gives the light a strange appearance since our eyes were never designed to observe coherent light.

Low-pass: A filter which allows low frequencies to pass while blocking high frequencies.

Octave: Musical terminology, meaning the doubling (or halving) of frequency. For example, one octave above "Concert pitch" A440 Hz is 880Hz, and one below is 220Hz. Musically, each of these frequencies is "A". One octave consists of 8 notes (hence octave) from A440 to A880 for example. The remaining musical notes are semitones (see Tempered Scale.

Oscilloscope: An electronic measurement tool which allows one to view a waveform. The vertical axis shows amplitude and the horizontal axis shows time.

Passive: Containing no devices which require a power supply. Passive devices include resistors, capacitors and inductors.

Phase: Hmmm. Tricky..... Ah-ha! Think of a bunch of soldiers all marching happily (?) to the sergeant's cries of "Hep, rah, hep-rah-hep" - except for Pt. Johnny who is blissfully "Rah, hep, rah-hep-rah"-ing. He is 180 degrees out-of-phase with the rest (or vice-versa). So it is with musical signals, where some signals have a "phase angle" (phase is measured in degrees of rotation) which is different from other signals.

Power Amp: An amplifier that is designed to drive loudspeakers or other relatively low impedance loads. Usually combines voltage and current amplification. May be integrated with the preamp (see below).

Preamp: Multiple meanings, but in hi-fi generally refers to a separate section of circuitry that includes source switching, volume and balance controls (as well as tone controls in many cases). Used to raise the level from tape decks, turntables, CD players and other music sources to a level suited to the power amplifier.

PSpice: An extremely powerful Spice simulator found in the Cadence OrCAD and Allegro family products

Quasi: to some degree or in some manner, resembling. For example, a quasi complementary-symmetry output stage in an amplifier is not in fact complementary-symmetry, but appears to be, and acts in a similar manner.

Quiescent: being still or at rest, in an inactive state. The quiescent current in an amplifier is that current drawn when the amplifier is "at rest" - i.e. not amplifying a signal, but supplied with power.

Resistor: An electrical device which impedes (resists) current flow regardless of frequency. Basic unit of measurement is the Ohm.

Resonance: The natural frequency at which a physical body will oscillate. An example is when you blow gently across the top of a bottle, the enclosed air resonates at a frequency determined by the internal volume. Also refers to the natural resonance of loudspeaker drivers, cabinets and ports, or the frequency where an inductance and capacitance have the same impedance (this causes maximum impedance with a parallel circuit, and minimum impedance for series circuits).

RMS: Root Mean Squared. Applies to voltage and current, but is commonly (although incorrectly) applied to power. Defined as an alternating voltage (or current) which has exactly the same energy content (power) as the same value of direct current.

Semiconductor: Silicon (or various other materials) that are specially treated so as to form diodes, transistors, MOSFETs, light emitting diodes (LEDs) etc. The basis of all modern electronics.

Sigrity: Software from Cadence to simulate signal integrity

Specctra: A powerful Auto-Interactive PCB router found in the Cadence OrCAD and Allegro PCB tools

SPL: Sound Pressure Level, measured in decibels (dB). 74dB SPL is considered to be the level of normal speech at a distance of 1 metre. The threshold of hearing is 0dB SPL.

Tempered Scale: The division of an octave (double or half frequency) into musical notes (tones and semitones). Because there are 12 notes in an octave, the relationship is based on the 12th root of 2 (1.059463). Thus, one semitone above 1,000Hz is 1,059.463Hz.

Thermal Coefficient (1): Of expansion, describes the amount by which a material expands when heated. Commonly expressed as a percentage per degree Celcius so the exact size at various temperatures may be calculated. Knowledge of the expansion characteristics of different materials is important in high power semiconductor manufacture, since differing expansion rates may cause device failure due to temperature cycling fractures.

Thermal Coefficient (2): Of resistance, describes the change in resistance at various temperatures. Most metals have a positive temperature coefficient of resistance, which means that the resistance increases with increasing temperature. Carbon and some alloys have a negative temperature coefficient of resistance, so as temperature is increased, resistance decreases.

Thermal Resistance: The resistance of various materials to the passage of heat energy. Most electrical conductors are also thermal conductors, with the higher electrical conductivity materials usually having higher thermal conductivity. Important in the design of high power electronics, heatsinks, semiconductor casings, etc.

Total Harmonic Distortion (THD): the sum of all amplifier distortion components, plus system noise. THD measurements are sometimes quoted as THD+noise. Usually measured at specified frequencies and power levels.

Velocity: speed of motion or rapidity. In audio and electronics, we are concerned with the speed of a signal in air and a conductor. Speed (velocity) of sound in air is approximately 345 metres per second at sea level, but it varies with temperature and humidity. Speed of an electrical signal in a wire is approximately 3 x 108 metres per second, but may be influenced by ...

Velocity Factor: a situation that occurs in conductors that are close to another conducting material. For example, a coaxial cable has an inner and outer conductor, with insulation between the two. The velocity factor of such cables varies from 0.7 to 0.9 (i.e. the signal travels slower than in free space).

Via: a joining drill hole in a PCB, plated or non-plated stitching two or more planes or layers together. A via allows a track to be routed onto another signal layer

Volt: The basic unit of "electromotive force". One Volt applied to a resistance of one Ohm will force a current of one Ampere to flow (Abbreviation - V).

Watt: The basic unit of power. 1 Volt across 1 Ohm (giving 1 Amp) dissipates 1 Watt (all as heat with a resistive load).

Wavelength: the length of one cycle of an AC signal. Determined by Wavelength = c / f where "c" is velocity and "f" is frequency. The wavelength of a 345Hz audio signal in air is one metre.

Xenon: A gas commonly used in flash tubes, HID (High Intensity Discharge) automotive headlamps and cinema projection lamps, and having an intense white light output with a colour temperature close to that of daylight.