Glossary of Audio Terminology

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Index | References



W3 An abbreviation for World Wide Web.

Waveform the shape of a graph of a varying quantity of a signal against time. An instrument called an oscilloscope can be used to pictorially represent the wave as a repeating image on a CRT screen.

wavelength Symbol (Greek lower-case lambda) The distance between one peak or crest of a sine wave and the next corresponding peak or crest. The wavelength of any frequency may be found by dividing the speed of sound by the frequency.

WDM ( wave division multiplexing) see DWDM

weighting filters Special filters used in measuring loudness levels, and consequently carried over into audio noise measurements of equipment. The filter design "weights" or gives more attention to certain frequency bands than others. The goal is to obtain measurements that correlate well with the subjective perception of noise. Weighting filters are a special type of band-limiting filters designed to compliment the way we hear. Since the ear's loudness vs. frequency response is not flat, it is argued, we should not try to correlate flat frequency vs. loudness measurements with what we hear.

  • ANSI A-weighting 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, so it tends to heavily roll-off the low end, with a more modest effect on high frequencies. It is basically the inverse of the 30-phon (or 30 dB-SPL) equal-loudness curve of Fletcher-Munson. [Note: Low-cost audio equipment often list an A-weighted noise spec; not because it correlates well with our hearing, but because it helps "hide" nasty low-frequency hum components that make for bad noise specs. Sometimes A-weighting can "improve" a noise spec by 10 dB! Words to the wise: always wonder what a manufacturer is hiding when they use A-weighting!]
  • ANSI C-weighting The C-curve is basically "flat," with -3 dB corners of 31.5 Hz and 8 kHz, respectively.
  • CCIR 468-weighting 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 CCIR 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).
  • CCIR ARM-weighting or CCIR 2 kHz-weighting This curves derives from the CCIR 468-curve above. Dolby Laboratories proposed using an average-response meter with the CCIR 468-curve instead of the costly true quasi-peak meters used by the Europeans in specifing 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 CCIR ARM (average response meter), as well as the CCIR 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)

white noise Analogous to white light containing equal amounts of all visible frequencies, white noise contains equal amounts of all audible frequencies (technically the bandwidth of noise is infinite, but for audio purposes it is limited to just the audio frequencies). From an energy standpoint white noise has constant power per hertz (also referred to as unit bandwidth), i.e., at every frequency there is the same amount of power (while pink noise, for instance, has constant power per octave band of frequency). A plot of white noise power vs. frequency is flat if the measuring device uses the same width filter for all measurements. This is known as a fixed bandwidth filter. For instance, a fixed bandwidth of 5 Hz is common, i.e., the test equipment measures the amplitude at each frequency using a filter that is 5 Hz wide. It is 5 Hz wide when measuring 50 Hz or 2 kHz or 9.4 kHz, etc. A plot of white noise power vs. frequency change is not flat if the measuring device uses a variable width filter. This is known as a fixed percentage bandwidth 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 power 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.]

Wi-Fi  (Wireless Fidelity) Catch all term for RF wireless networking protocols but most commonly refers to the 802 series.

802.11b wireless Ethernet broadcast in the 2.4GHz band.  May experience interference form 2.4GHz wireless phones and some microwave ovens. Supports a obstacle free transmission distance of approximately 300 meters (1000 Ft.) but the speed of transmission drops rapidly form the upper limit of 11Mbps as distance increases ( to as low as 2Mbps at the 300 meter distance). 

802.11a is a variant that transmits in the 5GHz band (sometimes called Wi-Fi 5 ).  It offers a max transmission speed of 54Mbps.  There is less interference in the 5GHz band but the higher frequencies have trouble getting through objects such as office walls and ceilings. 802.11a is rated for a obstacle free transmission distance of approximately 600 meeters(2000 Ft.) but in practice is actually much shorter that 802.11b.  Many people have broken the the encryption scheme of 802.11b, however the encryption used in 802.11a seams to be more robust.

802.11g is the newest Wi-Fi protocol.  It offers the same max transmission speed of 54Mbps as 802.11a.  It transmits however on the same 3.4GHz band as 802.11b.  The protocol has a stronger encryption that 802.11b.  Because that both transmit in the same frequencies it is common to find combo devices capable of supporting simultaneous connections both 802.11a and 802.11g clients (sometimes referred to as 802.11a/g)

Wireless A range of technologies that replace wired connections with RF, IR or EM signals.

word An ordered set of bits that is the normal unit in which information may be stored, transmitted, or operated upon within a given computer - commonly 16 or 32 bits.

word clock The synchronizing signal that indicates the sampling frequency or rate of sample words over a digital audio interface.

word length The number of bits in a word.

World Wide Web (WWW and/or W3) A way to present resources and information over the Internet, or according to its inventor CERN (European Laboratory for Particle Physics), "The World Wide Web (W3) is the universe of network-accessible information, an embodiment of human knowledge."

WPAN (Wide Personal Area Network) is a trademark of the IEEE for the same protocol as Bluetooth.  See Bluetooth.

write To record data on a medium.

WSDL (Web Services Definition Language) A protocol that describes a Web service's capabilities.

WWW (World Wide Web) See: World Wide Web.



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