GLOSSARY
Since EVPs deal with audio I feel it is appropriate that any evp investigator should have a good grasp of audio terminology. That is why alot of the definitions below deal with audio terminology more then paranormal definitions. A good grasp of both will only help you.

A
AIFF - Short for Audio Interchange File Format, a common format for storing and transmitting sampled sound, developed by Apple Computer and the standard audio format for Macintosh computers. Files are 8-bit mono or stereo and generally end with a .AIF or .IEF extension. Normal AIFF does not support data compression so files tend to be large, but another format called AIIF-Compressed (AIFF-C or AIFC) does support compression.
Amplitude - The 'level' (perceived as 'volume') of an electrical or acoustic signal. Shown as the value of the vertical axis on a typical graph of a sound wave.
Analog - Of, relating to, or being a device in which data are represented by continuously variable, measurable, physical quantities, such as length, width, voltage, or pressure.
AVI - Short for Audio Video Interleave, the file format for Microsoft's Video for Windows standard.
B
Bandwidth - The total frequency range of any system. Usually specified as something like: 20-20,000Hz plus or minus 3 db.
Bandpass Filter - An electric circuit designed to pass only middle frequencies.
Bass - Lower register of pitch; also a stringed musical instrument designed to play low frequency sounds; also a voice lower in pitch than a baritone.
C
Cardioid - "Heart" shaped pattern exhibited by some microphones which reduces pick-up from the sides and back.
Clipping -Audible distortion occurring when the peaks of an amplifier's output are flattened ('clipped'). When the input is too high, an amplifier has insufficient power to accurately reproduce the output waveform.
Compression (Audio) - The process of reducing the dynamic range of a given analogue audio program by making the loud parts quieter and the quiet parts louder.
Compression (Data) -The process of packing digital data, such as computer files, more efficiently for the purpose of storage or transmission. Commonly referred to as 'stuffing' or 'zipping' a file.
Compression (Audio/Video Files) - A process of temporarily or permanently reducing audio data for more efficient storage or transmission. A temporary reduction in file size is called 'non-lossy' compression, and no information is lost. A permanent reduction in file size (such as with mp3 files) is called 'lossy' compression, and involves discarding (supposedly) unnecessary information which is irretrievably lost.
Compression Ratio -See Ratio
Compressor - A type of dynamic range processor which reduces the gain of audio signals which are over an adjustable 'threshold' level, therefore reducing the dynamic range. Generally allows the operator control over threshold, ratio, attack and release times. Both analogue and digital types are available.
Condenser Microphone - A mic that depends on an external power supply or battery to electrostatically charge its condenser plates. Also called a 'Capacitor' microphone.
D
Decibel or dB - A logarithm of a ratio used to indicate mathematically how a measured quantity compares to a standard reference quantity. One use, of many, is to represent Sound Pressure Levels (SPL) as numbers from 0dB (the softest sound that may be heard) to 120dB and beyond (the level at which sound is perceived as pain).
Digital -Represented by a numerical code. For sound, the conversion of an analogue waveform to a series of numbers representing the instantaneous amplitude for each sample taken, the storage of those numbers, and the eventual conversion back to analogue format for replay.
Distortion - Any difference, apart from level, between an original signal and one that has been processed. One cause may be the overloading of the input stage of an amplifier, but many other forms of distortion, such as harmonic distortion are common.
Dynamic Microphone - A microphone that converts sound into electrical energy by means of a moving coil located in a magnetic field.
E
EMF (Electro-Magnetic Field) -The amount of magnetic energy that can accumulate around us, both naturally and man-made.
EMF Detector - Handheld scientific instruments that can pick up electronic and magnetic fields over various frequencies.
EQ / Equalization - The increase or decrease in level of certain portions of the audio frequency spectrum imposed by a device or acoustic environment.
Expander - A type of dynamic range processor which reduces the gain of audio signals which are under an adjustable 'threshold' level, therefore increasing the dynamic range. Generally allows the operator control over threshold, ratio, attack, release and 'hold' times. Both analogue and digital types are available.
F
Filter - A device that removes unwanted frequencies or noise from a signal.
Formant - Any of several prominent bands of frequency that determine the phonetic quality of a vowel
Frequency - The number of complete cycles that a sound wave goes through in each second. Unit used is Hertz, abbreviated to Hz, although some countries still use the older term 'cycles per second' (cps). Humans perceive frequency subjectively as pitch (eg: 440Hz = A).
G
Gain - The amount by which an amplifier increases the power of a signal, indicated either in dB (e.g. Gain = +12dB), or as a multiplier (e.g. Gain = x4)
H
Hertz - (Abbreviation: Hz) The unit of frequency. Replaces 'cycles per second' and means the same.
High Pass Filter - A circuit that discriminates between high and low frequencies and allows only the high frequencies to pass.
Hypercardioid - A narrower heart-shaped pick-up pattern than that of cardioid microphones.
I
Impedance - The measure of the total resistance to the current flow expressed in ohms (‡), in an alternating current circuit. It is an important characteristic of electrical devices (particularly speakers and microphones). Most speakers are rated at 4 or 8 ohms. Microphones are usually classified as being either high impedance (10,000 ohms or greater) or low impedance (50 ohms to 600 ohms).
Input Overload Distortion - Distortion caused by too great an input signal being sent to an amplifier or preamplifier. It is not affected by volume control settings and often occurs when mics are positioned too close to the sound source. This distortion is controllable through the use of an attenuator or pad.
Inverse Square Law - The law that states that in the absence of reflective surfaces, sound pressure (or light) falls off at a rate inverse to the square of the distance from its source. In other words, every time you double your distance from the sound source, the sound pressure level is reduced by a factor of 4, or 12 dB.
ITC (Instrumental TransCommunication) - Describes the various modes of video and audio format communication.
L
Limiter - A compressor set up with a high ratio (in excess of 10:1) and used primarily to prevent a signal from exceeding a certain pre-set maximum level.
Lossy Compression - A type of data compression which permanently discards data that humans supposedly "cannot hear" to create much smaller audio, video and image file sizes. When the file is decompressed by the recipient, this compression method replaces the data for the sections it removed with calculated values to restore the file. The decompressed file is similar but not identical to the original file.
Low Pass Filter - A circuit that discriminates between high and low frequencies and allows only the low frequencies to pass.
M
Mac - Apple Macintosh computer.
Matrixing - Natural tendency for the human mind to interpret sensory input (that which is perceived visually, audibly or tactilely) as something familiar or more easily understood and accepted, and in effect mentally "filling in the blanks." In essence you create something out of nothing.
Microphone - A device that converts sound pressure variations into electrical signals.
Midbass - Mid frequency bass, usually frequencies just above the sub-bass range, from around 100 - 400 Hz or so.
Monitors (Studio) - Speakers used in the control room of a recording studio. Generally of two types: Main Monitors for overall sound, and Reference Monitors used to check sound quality through less capable speakers, such as might be found in domestic environments.
MPEG - Short for Moving Picture Experts Group, and pronounced m-peg. The term also refers to the whole collection of digital compression standards and file formats developed by the group.
MP3, mp3: Is the file extension for MPEG, audio layer 3. Layer 3 is one of three coding schemes (layer 1, layer 2 and layer 3) for the compression of audio signals. Layer 3 uses perceptual audio coding and psychoacoustic compression to remove all superfluous information (that, in the opinion of the developers, the human ear doesn't hear anyway). It also adds an algorithm that increases the frequency resolution 18 times higher than that of layer 2. The result is mp3 encoding shrinks the original sound data from a CD by a factor of 12 without sacrificing sound quality.
N
Noise Gate - A special type of expander with a very high ratio (usually about1:100), often used to eliminate low-level hiss, noise or leakage. Especially effective wherever there is a high level of ambient noise, such as around a drum kit.
Non-Lossy Compression - A form of data compression which seeks out chunks of data which are identical, replacing them with markers called keys. In this way, the file is reduced in size, and when it is decompressed by the recipient, the keys are replaced with the large chunks of data that were originally there (this is called Run Length Encoding). Using non-lossy compression, the uncompressed file is identical to the original file.
O
Omnidirectional - Capable of picking-up sound equally from all directions (for microphones) or radiating sound equally in all directions (for speakers).
P
Pad - An electrical circuit used to attenuate or reduce the amplitude of an audio signal by a fixed amount, e.g a -15dB pad reduces the signal by a fixed 15 decibels.
PCs - Personal computers. This term is generally used for IBM-compatible, Intel-based computers running DOS or Windows.
Phantom Power - Operating voltage (usually 48 Volts DC) supplied to a condenser mic by a mixer or external power source along normal mic leads.
Phase - The relationship of an audio signal or sound wave to a specific time reference.
Pitch - The subjective sensation produced by various frequencies. The higher the frequency, the higher the perceived pitch; however, frequency is not linearly related to pitch.
Polarity - A condition with two states (+ve or -ve) and is usually defined in one of three ways: 1. Acoustical to electrical (microphone): Positive pressure at diaphragm produces positive voltage at pin 2 of XLR or at the tip of a 1/4-inch phone plug. 2. Electrical to acoustic: Positive voltage into the "plus" terminal of a speaker causes the speaker's diaphragm to move forward to produce positive pressure. 3. Electrical to electrical: Positive voltage into pin 2 of an XLR jack produces positive voltage at the output (pin 2 of an XLR plug, the tip of a 1/4-inch phone jack, or the red (plus) connector of a binding post (banana terminal).
Proximity Effect - An increase in the bass response of some mics as the distance between the mic and its sound source is decreased.
Q
Q - Referring to the bandwidth of one band of a parametric equaliser, Q is calculated by dividing the centre frequency in Hz by the width of the boost or cut zone +3dB or -3dB above or below 0dB. For example, a gentle boost centred at 1000Hz which extends from 750Hz to 1250Hz measured 3dB above flat has a Q of 1000/500 = 2. By comparison, a deep notch centred at 1000Hz which extends from 995Hz to 1005Hz measured -3dB above flat has a Q of 1000/10 = 100.
QuickTime - A video and animation system developed by Apple Computer and built into the Macintosh operating system. It is used by most Mac applications that include video or animation. PCs can also run files in QuickTime format, but they require a special QuickTime driver. QuickTime supports most encoding formats, including Cinepak, JPEG, and MPEG. QuickTime is competing with a number of other standards, including AVI and ActiveMovie.
R
Radio-frequency interference (RFI) - Radio-frequency sound waves can be caused by many sources including; shortwave radio equipment, household electrical line, computers and many other electronic devices. RFI sometimes interferes with audio signals, causing noise and other distortions.
Ratio - One of the parameters which can be varied on dynamic range processors such as compressors and expanders. It represents the compression or expansion ratio between input and output levels. A compressor with a 2:1 ratio would reduce the output gain to half of the input value above the threshold. An expander with a 1:80 ratio would reduce the output gain to 1/80th of the input value below the threshold.
Ripper - A software program that "grabs" digital audio from a compact disc and transfers it to a computer's hard drive. The integrity of the data is preserved because the signal does not pass through the computer's sound card and does not need to be converted to an analog format. The digital-to-digital transfer creates a WAV file that can then be converted into an MP3 file.
S
Saturation (Tape) - The distortion caused by magnetic recording media being unable to store as much high frequency information as low frequency information.
Scrubbing - The process of moving within an audio file or tape to audibly locate a particular section. The term originally comes from the days of reel-to-reel players, when rocking a reel would give the impression of scrubbing tape across the head. Many audio scrub tools today allow the user to drag a cursor across the wave form to audition different sections of the audio file.
Sibilance - The distortion of sibilants by recording and reinforcement systems incapable of handling the high frequencies present in such sounds. See also "Saturation".
Sibilants - High frequency sounds in speech, such as "S", "F" & "T".
Signal Processors - Electronic devices which alter sound either to achieve a particular effect or to solve a problem with that sound (e.g. delays, compressors, reverbs, noise gates, equalisers).
Streaming - A technique for transferring data such that it can be processed as a steady and continuous stream. Streaming technologies are often used on the Internet because most users do not have fast enough access to download large multimedia files quickly, so the client browser or plug-in can start displaying the data before the entire file has been transmitted.
T
Timbre - The combination of harmonic frequencies in voices or instruments which give them their characteristic quality. Synonyms: 'Quality', 'Sonority', 'Tone Colour'.
U
USB - An external peripheral interface
standard for communication between a computer and external
peripherals over an inexpensive cable using biserial
transmission.
V
Volume - Loudness of sound; a subjective sensation dependent on the amplitude of a sound wave or electrical signal, but not linearly related to it.
WAV - The format for sound files developed jointly by Microsoft and IBM, and built into Windows 95 which made it the de facto standard for sound on PCs. WAV sound files end with a.wav extension and can be played by nearly all Windows applications that support sound.
Waveform - A graphical representation of a signal as a plot of amplitude versus time, i.e. the shape of a wave.