## W
**A-weighting**(not official but commonly written as**dBA**) The A-curve is a wide bandpass filter centered at 2.5 kHz, with ~20 dB attenuation at 100 Hz, and ~10 dB attenuation at 20 kHz, therefore it tends to heavily roll-off the low end, with a more modest effect on high frequencies. It is the inverse of the 30-phon (or 30 dB-SPL) equal-loudness curve of Fletcher-Munson.**C-weighting**(not official but commonly written as**dBC**) The C-curve is "flat," but with limited bandwidth, with -3 dB corners of 31.5 Hz and 8 kHz, respectively.
**ITU-R 468-weighting**(*was CCIR, but since the CCIR became the ITU-R, the correct terminology today is ITU-R*) This filter was designed to maximize its response to the types of impulsive noise often coupled into audio cables as they pass through telephone switching facilities. Additionally it turned out to correlate particularly well with noise perception, since modern research has shown that frequencies between 1 kHz and 9 kHz are more "annoying" than indicated by A-weighting curve testing. The ITU-R 468-curve peaks at 6.3 kHz, where it has 12 dB of gain (relative to 1 kHz). From here, it gently rolls off low frequencies at a 6 dB/octave rate, but it quickly attenuates high frequencies at ~30 dB/octave (it is down -22.5 dB at 20 kHz, relative to +12 dB at 6.3 kHz).
**K-weighting**Used for loudness normalization in broadcast, it "... is composed of two stages of filtering; a first stage shelving filter and a second stage high-pass filter." [from ITU-R BS.1770-2, page 3.
**RLB-weighting (**Used for loudness normalization in broadcast, it is a second-order high pass with a -3 dB corner fixed at 60 Hz. See ITU-R BS.1770-1 , page 4.*revised low-frequency B curve*)
**TU-R (CCIR) ARM-weighting**or**ITU-R (CCIR) 2 kHz-weighting**This curves derives from the ITU-R 468-curve above. Dolby Laboratories proposed using an average-response meter with the ITU-R 468-curve instead of the costly true quasi-peak meters used by the Europeans in specifying their equipment. They further proposed shifting the 0-dB reference point from 1 kHz to 2 kHz (in essence, sliding the curve down 6 dB). This became known as the ITU-R ARM (*average response meter*), as well as the ITU-R 2 kHz-weighting curve. (See: R. Dolby, D. Robinson, and K. Gundry, "A Practical Noise Measurement Method,"*J. Audio Eng. Soc.*, Vol. 27, No. 3, 1979)**[***Before using these terms be aware that the ITU-R, even after 20 years, takes strong exception to having its name used by a private company to promote its own methodologies.*]
**Z-weighting**A new term defined in IEC 61672-1, the latest international standard for sound pressure level measurements. It stand for*zero-weighting*, or no weighting; i.e., a flat measurement with equal emphasis of all frequencies.
Sir
Charles Wheatstone (1802-1875) received credit for its invention
because of his adaptation of the circuit in 1843 for the measurement of
resistance. Wheatstone also invented the concertina, the stereoscope and
contributed significantly to the development of the telegraph.]
not flat
if the measuring device uses a variable width filter. This is known as
a filter. A common example of
which is 1/3-octave wide, which
equals a bandwidth of 23%. This means that for every frequency measured
the bandwidth of the measuring filter changes to 23% of that new center
frequency. For example the measuring bandwidth at 100 Hz is 23 Hz wide,
then changes to 230 Hz wide when measuring 1 kHz, and so on. Therefore
the plot of noise power vs. frequency is not flat, but shows a 3 dB rise
in amplitude per octave of frequency change. Due to this rising frequency
characteristic, white noise sounds very bright and lacking in low frequencies.
[Here's the technical details: noise fixed percentage bandwidthpower is actually its power
density spectrum - a measure of how the noise power contributed by
individual frequency components is distributed over the frequency spectrum.
It should be measured in watts/Hz; however it isn't. The accepted
practice in noise theory is to use amplitude-squared as the unit
of power (purists justify this by assuming a one-ohm resistor load). For
electrical signals this gives units of volts-squared/Hz, or more
commonly expressed as volts/root-Hertz. Note that the denominator
gets bigger by the square root of the increase in frequency. Therefore,
for an octave increase (doubling) of frequency, the denominator increases
by the square root of two, which equals 1.414, or 3 dB. In order for the
energy to remain constant (as it must if it is to remain white noise) there
has to be an offsetting increase in amplitude (the numerator term) of 3
dB to exactly cancel the 3 dB increase in the denominator term. Thus the
upward 3 dB/octave sloping characteristic of white noise amplitude when
measured in constant percentage increments like 1/3-octave.] See noise
color. 2. Music. Slang term for music that is discordant with
no melody; disagreeable, harsh or dissonant.
Captain of the Universe.
Wireless
Control of RPM Series Drag Net Programmable Processors.
**C****lass 1**Where*both*fire and shock hazards exist, i.e., the wiring can deliver enough current for a fire hazard and enough voltage for a shock hazard. The most common example is AC power running to equipment. This class requires prevention of all touching and barriers against fire.-
**Class 2**Where*neither*fire or shock hazard exists, i.e. the wiring cannot deliver enough current (internal limiting) for a fire hazard and not enough voltage for a shock hazard. Examples here are all normal audio interconnect plus most power amplifier output wiring. -
**Class 3**Where there is not a fire hazard*but there is a shock hazard*, i.e., the wiring cannot deliver enough current (internal limiting) for a fire hazard, but can deliver enough voltage for a shock hazard. Requires touch-proof terminals; seen in audio for very high-output power amplifiers.
1. A way to present resources and information over the Internet,
or according to its inventor, British scientist Tim
Berners-Lee, while at CERN in 1989, "The
World Wide Web (W3) is the universe of network-accessible information,
an embodiment of human knowledge." 2. Satirically called the W3)World Wide
Wait.
.
Rowan and Martin's Laugh-In. |