Ashly Parametric Equalizers SC-63 - Manual (Page 17)

DEFINITION OF TERMS AS USED IN THIS MANUAL
ACTIVE
Electronic circuits which use devices such as transistors and integrated
circuits, and which are capable of voltage and power gain as well as
loss. Circuits using only resistors, capacitors, transformers, etc., are
referred to as passive.
AMPLITUDE
The voltage level of a signal. May be measured in volts or decibels.
Generally corresponds to the volume or intensity of an audio signal.
BALANCED
A 3-wire circuit arrangement in which two conductors are designated as
signal lines (+ and -), and the third is a shield and chassis ground. The
signal lines are of opposite polarity at any given moment, and are of
equal potential with respect to ground. Balanced input amplifiers are
used on all Ashly SC series products to improve hum and noise rejection.
Jumpering signal minus (-) to ground provides an unbalanced input.
CENTER FREQUENCY
The frequency (or pitch) at which a filter is most effective. In a
parametric equalizer, it refers to the frequency where a particular
boost/cut control has maximum effect.
dB
A unit by which audio levels can be COMPARED. Often thoroughly
misunderstood are the concepts that decibels represent the level of a
signal compared to some reference level (15 dB cut means a certain level
less than a previous level --- the absolute level of the signal need not
be known), and that decibels are a logarithmic unit.
Some handy numbers to remember when dealing with decibels:
dBm
+3 dB = Double Power
+6 dB = Double Amplitude, Quadruple Power
+ 10 dB = 10X Power
+20 dB = 10X Amplitude, 100X Power
A unit of measurement in decibels where 0 dBm = a power level of 1
m illiwatt into a 600 ohm load. Originally defined by the telephone
company to measure line levels.
dBV
Decibel Volts, an update of the dBm definition where 0 dBV = the same
voltage level as 0 dBm, but with no regard to power or impedance. 0 dBV =
0.778 Volts. This unit is much more appropriate for modern audio
equipment with high impedance inputs and low impedance outputs.
DISTORTION
Generally refers to ANY modification of an audio signal which produces
new frequencies which were not in the original. Examples are harmonic
distortion, where a circuit adds overtones to a fundamental signal, and
intermodulation or IM distortion, where two frequencies beat together to
produce sum and difference frequencies.
FEEDBACK
Generally refers to any process where an output is in some form routed
back to an input to establish a loop. Negative feedback tends to be be
self stabilizing, while positive feedback causes instability.
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