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Glossary – D

Prevention of vibrations, responses, or resonances that would cause distortion if unchecked. Mechanical control is by friction; electrical control is by resistance. Damping is a measure of a power amplifier's ability to control the back-emf motion of the loudspeaker cone after the signal disappears. The damping factor of a system is the ratio of the loudspeaker's nominal impedance to the total impedance driving it. A technique for stabilizing an electronic or mechanical device by eliminating unwanted or excessive oscillations. The reduction of movement of a speaker cone, due either to the electromechanical characteristics of the speaker driver and suspension, the effects of frictional losses inside a speaker enclosure, and/or by electrical means. Any effect, either deliberately engendered or inherent to a system, that tends to reduce the amplitude of oscillations of an oscillatory system.
For any underdamped motion during any complete oscillation, the quotient obtained by dividing the logarithmic decrement by the intensity over the whole sphere surrounding the projector to the intensity on the acoustic axis.
Description of a sound in which reverberant information is severely attenuated, or missing completely.
In acoustics, a place at which a train of sound waves is cancelled by reflections arriving out of phase with the wanted signal thus creating an area of silence or poor audibility.
The fall-off in amplitude when a force applied to a vibrating device is removed.
The time it takes for echoes and reverberation to die away.
A unit of level equal to ten times the logarithm of the ratio of two powers. Depending on the reference level used, the decibel symbol will be immediately followed by a letter, as: dBA - An "A" weighted decibel level. dBB - A "B" weighted decibel level. DBC - A "C" weighted decibel level. dBm - A decibel level in which Pb represents one milliwatt of power dissipated in a 600 ohm line. Pa must a also be measured in a 600 ohm line. DBV A decibel voltage level, in which the reference, Vb, is 1.0 volt. A reference of 0.775 volts is also frequently used.
The process of applying complementary signal processing to restore a signal to its normal state, as in the playback mode of a noise reduction system.
A compressor designed to minimize sibilants.
Any of several devices used to erase recordings on magnetic tapes and films or to demagnetize magnetic recording heads.
The time interval between a direct signal and its echo(es).
Any device that introduces a time delay between its input and output.
A delay line, in which the delay is accomplished acoustically, as in a long tube with a speaker at one end and a microphone at the other.
A delay line, in which the delay is accomplished electronically, via an analog/digital and digital/analog conversion.
The erasure of a magnetic tape, or the degaussing of the tape recorder heads.
More distant instruments produce a greater amount of reverberation in proportion to direct sound than closer ones, thereby giving the illusion of depth. Near sound sources propagate spherical wavefronts whereas distant ones have a nearly plane front. So for the same angle of incidence there is a greater phase difference across a stereo microphone pair for a near than a far sound. This adds to the effect of depth.
The ability of the listener to perceive the apparent relative distances of various instruments in a recording (or live concert).
The moving membrane in a microphone or loudspeaker.
The interior of a microphone is comprised of a permanent magnet, a coil of wire and a diaphragm which, like the eardrum, vibrates to changes in air pressure. The vibration of the diaphragm in conjunction with the permanent magnet and the coil converts changes in air pressure into changes in electrical voltage. As air pressure increases, the diaphragm within the microphone is pushed towards the back of the microphone, inducing a voltage; as pressure decreases, the diaphragm travels outwards inducing a voltage in the opposite direction. Like the eardrum, the diaphragm will move in a parallel motion to the movement of the example sound, the vibrating bass drum skin. The resulting voltage will be a continuous parallel voltage image of the movement of that bass drum skin.
Once sound has been converted to an electrical voltage, the "voltage image" can be amplified and then used to drive speakers. Like the skin of the bass drum, the movement of the speaker diaphragm compresses and decompresses air to produce sound. If the voltage is going upwards, the speaker will travel outwards; if the voltage is going downwards, the speaker will travel inwards. The resulting movement of the speaker will be parallel to the movement of the skin on the bass drum, to the movement of an eardrum, to the movement of the diaphragm within the microphone, and to the induced voltage.
The bending of a sound wave, as it passes over an obstacle. The angle of diffraction is a function of wavelength.
The extent to which sound waves are broken up by uneven surfaces.
German industrial standard.
Flow of electrons from a negatively charged body to a positively charged body.
The dynamic range available on a disc is limited mainly by the master-tape recording. To extend it, some recordings have been made directly on to the master disc as were the old 78 r.p.m. records. Mothers, stampers and pressings are then made from it in the usual way. The whole of one side of an LP must be recorded without fault in one take, a difficult undertaking for the performers. Many lacquers are scrapped before a satisfactory master is produced.
A console output, taken directly from an input module and bypassing the pan pots and bus selector switches.
A transformer pickup of a musical instrument, in which the instrument's amplifier output is fed directly to the console, via a matching transformer.
A speaker in which the radiating element acts directly on the air instead of relying on any other element, such as a horn.
The sound that reaches the listener via a straight line path from the sound source. A sound with no echoes or reverberation. The sound heard from a transformer pickup.
The variation in response for different angles of sound incidence. The polar response of a transducer.
A rejection figure, stated in dB units, indicating the attenuation of sound inciding from an angle relative to the zero position. For supercardioid mikes the angle of best rejection is at 235, for cardioid at 180.
To make a comparison between various microphones, this term was introduced to indicate the power output of a nondirectional mike in relation to a directional mike of equal sensitivity in a diffuse sound field. An ideal cardioid mike has a DC of 3. Since the intensity of sound decreases as the square of the distance, the cardioid mike may be used at a distance of 1.7 times farther than a nondirectional mike with the same amount of disturbing ambient noise.
The signal from a tape player (or from a recording console, in case of direct-to-disc recordings) is fed to the disc cutter and modified to the RIAA recording characteristic. It is pre-sampled 1.1 seconds ahead of the main playback head to provide a control signal for the cutter-head radial drive, or the main cutter signal may be delayed. By this means groove spacing can be varied according to the amplitude of the signal, thereby achieving maximum playing time. Spacing can vary from 130 to 390 grooves per inch. A heated triangular chisel, actuated by two helium-cooled coils. cuts the groove in a lacquer-coated aluminum disc 14 inches in diameter for a 12 inch record and 10 inches for a 7 inch.
The main materials used to produce LP records are a vinyl copolymer, a stabilizer, a lubricant, and a pigment, usually carbon black. The latter produces the traditional black color, but other colors including white have been used. These are compounded and extruded or fed into the press in the form of small cakes. Disc material is subject to two types of deformation during playing: elastic, from which it returns, hence is temporary; and plastic, which is permanent, in case of records it is termed "wear".
The splitting of a complex sound wave into its various frequency components, as the sound wave passes from one medium to another.
The distance between the position of a moving object such as a speaker diaphragm, and its original position.
The placement of a microphone, or microphones, relatively far from the sound source, thus picking up a larger proportion of reflected sound.
Deviations from an original sound that occur in the reproduction process. Harmonic distortion disturbs the original relationships between a tone and other tones naturally related to it. Intermodulation distortion introduces new tones that result from the beating of two or more original tones.
The appearance of harmonics of the applied input signal, as measured at the output of an electronic component.
Distortion in the form of unwanted frequencies corresponding to the sums and differences between various components of a complex waveform.
The amount of distortion, measured as a percentage of the total waveform amplitude.
The presence of the third harmonic (3 x f) of an applied input signal, as measured at the output of an electronic component.
Distortion produced when an audio system is unable to accurately reproduce a transient.
Same as crossover network.
A reference tone, recorded at the head of a Dolby encoded tape, for alignment purposes.
A harmonic frequency that has a greater amplitude than the fundamental frequency.
A tone-cabinet design in which one or more speakers are rotated or in which a baffle is rotated to produce a mechanical vibrato/tremolo effect.
1. Mixing a slightly delayed signal with a direct signal, to simulate the effect of twice as many recorded instruments. 2. The generation of a large amount of second-harmonic distortion owing to a nonlinear motion of a speaker cone.
Flutter occurring at random rates. Long term deviation from the specified tape speed.
An undriven speaker cone mounted in a bass-reflex enclosure. A passive radiator.
On a magnetic recording tape, a momentary drop in output level, usually caused by an imperfection in the oxide coating.
A description of a sound which lacks reverberant information. The direct sound of a musical instrument.
Type of monophonic recorder which utilizes half of a standard 1/4-in tape in one direction and the other half in the opposite direction.
Copying of previously recorded material. In tape recording, playing a recorded tape on one machine while recording it on another. In film, synchronization with lip movements of an actor of a voice not originally recorded in sync with the picture. Loops, or short extracted sections of dialogue in composite form, are used to guide the actor or narrator. Used also to prepare foreign films for new markets.
Process of automatic compression, e.g. when the announcer's voice signal causes the level of music to be attenuated.
A form of bass-reflex speaker enclosure in which a tube is mounted behind the reflex port.Ducking -- Process of automatic compression, e.g. when the announcer's voice signal causes the level of music to be attenuated.
In German: Kunstkopf Stereo. System of recording using microphones placed in the ears of a model head (or of a wearer).
A magnetic phono pickup in which a moving coil in a magnetic field generates voltages to form an audio signal.
Alteration of volume range of a program when it is transmitted.
A microphone that operates on the same basic principle as a dynamic cartridge. A moving coil or ribbon microphone.
1. Of a recording, the range within which its volume fluctuates. (The term is applied to the original sounds and to the electric currents produced by them.) 2. In a musical instrument, a measure of the span between the quietest and loudest sounds it is capable of producing. 3. In a tape recorder, the dB interval between the noise level and the level at which distortion occurs.
A signal processing device whose operating parameters change as a reaction to the program content. For example, a compressor or expander. See Static Signal Processing Device.
Also termed a moving-coil speaker. The moving diaphragm is attached to a coil, which is conductively connected to the source of electric energy and placed in a constant magnetic field. The current through the coil interacts with the magnetic field, causing the coil and diaphragm to move back and forth in accordance with the current variations through the coil.
The unit of sound pressure. Originally called a bar, but now termed by the full expression. At the threshold of hearing, the acoustic force per unit area is 0.0002 dynes/cm2

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