BSS Audio DPR-901II Owner's Manual - Manual (Page 25)

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ACTIVE Active electronic circuits are those capable of voltage and power gain by
using transistors and integrated circuits. Passive circuits are those which
use only resistors, capacitors, transformers, etc.
BALANCED Refers to a 3-wire connection in which two of the wires carry the signal,
and the third acts as a shield, tied to chassis ground. The two signal lines
are of opposite polarity at any instant, but are at the same (numeric)
voltage with respect to ground. Balanced connections are used to reject
noise and hum pickup in system inter-connections.
BELL Descriptive term for equalisation cut or boost which occurs symmetri-
cally either side of the centre frequency. The frequency response graph
takes on the shape of a (church) bell.
CLIP Another name for overload; when a signal reaches an amplifier’s output
voltage or current limits. Clipping is not harmful in itself, but produces
severe distortion and exacerbates heat-dissipation in the amplifier, its
power supply and the speaker(s).
COMPRESSION Making a signal smaller in proportion to its magnitude. Normally this
occurs above a threshold that is near or above the average signal magni-
tude.
The more the signal exceeds the threshold, the more it’s reduced, caus-
ing all signals above the threshold to be reduced to a similar level. This
increases the density of the sound level distribution in time, giving a
characteristic ‘thickening’ effect to the sonics. The ratio of reduction
determines how much the variation in signal magnitude is condensed:
high (10:1) ratios reduce large (20dB+) variations to scarcely audible
fluctuations of less than 2dB. See EXPANSION for a table of ratios.
Compression can also take place below a given threshold, but this
facility is rarely if ever found on existing compressors.
dB A unit for expressing the ratio between two signal levels, for comparison
purposes. On its own, it has no absolute value. Rather, it’s a logarithmic
ratio used to express the differences between two amounts or levels.
Positive numbers indicate an increase, and negative ones a decrease.
Some useful ratios are:
+3dB = double power or 1.5x voltage
+6dB = 4x power; or 2x voltage
+10dB = 10x power; or 3x voltage
+20dB = 100x power; or 10x voltage
dBm The addition of ‘m’ after dB indicates an absolute scaling for the dB ratio.
Instead of a ratio, the dB then becomes a measure of power. 0dBm = a
power level of 1 milliwatt into a load of 600 ohms. The corresponding
voltage is 778mV (0.778v). In modern audio, the dBm is loosely used to
Appendix C Glossary
Glossary