This refers to a weighted noise measurement for a Dolby B
type noise reduction system. A filter characteristic is used
that gives a closer correlation of the measurement with the
subjective annoyance of noise to the ear. Measurements
made with this filter cannot necessarily be related to un-
weighted noise measurements by some fixed conversion
factor since the answers obtained will depend on the spec-
trum of the noise source.
Definition of Terms (Continued)
is also an excellent equation to determine the 3 dB point of a
closed-loop gain, assuming that you know the GBWP of the
device. Refer to the diagram on the following page.
Biamplification: The technique of splitting the audio fre-
quency spectrum into two sections and using individual
power amplifiers to drive a separate woofer and tweeter.
Crossover frequencies for the amplifiers usually vary be-
tween 500 Hz and 1600 Hz. “Biamping” has the advantages
of allowing smaller power amps to produce a given sound
pressure level and reducing distortion effects produced by
overdrive in one part of the frequency spectrum affecting the
other part.
S.P.L.: Sound Pressure Level — usually measured with a
microphone/meter combination calibrated to a pressure level
of 0.0002 µBars (approximately the threshold hearing level).
=
S.P.L. 20 Log 10P/0.0002 dB
where
P
=
is the R.M.S. sound pressure in microbars.
2
=
=
(1 Bar 1 atmosphere 14.5 lb/in
194 dB S.P.L.).
C.C.I.R./A.R.M.:
Literally: International Radio Consultative Committee
Average Responding Meter
DS011833-16
www.national.com
18
NSC [ National Semiconductor ]
