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Dictionary of Audio Terminology - Z

Z - The symbol for impedance.

z-axis - One of three axes in a three-dimensional Cartesian coordinate system.

Z-domain - The discrete time domain. Contrast with s-domain.

zener or zener diode - A two terminal semiconductor device commonly use in power supply reference circuits. It exhibits a stable voltage over a wide range of currents passing through it, creating a constant-voltage characteristic.

zenith - Pertaining to the angular alignment of a tape head along its vertical axis and at right angles to its azimuth; a forward/backward tilt of the head, when viewed from the front.

Zeptosecond Abbr - zs or zsec - One sextillionth (10-21) of a second.

zero - Half of all the stored knowledge in computers. Compare with one; See Kaplan's The Nothing That Is for its fascinating story.

zero-based mixing. Rick Chinn of Uneeda Audio explains it this way:
"Zero-based mixing refers to starting the mix with all faders down, then listening to the stage sound, and only adding those sources to the mix that can't be heard in the house. The goal is to minimize the build in volume level caused by amplification and to make the overall performance as acoustical as possible." "Things that work against zero-based mixing are Really Large Venues, loud monitors, and highly directional, but loud instruments such as trumpets which need the sound system for coverage rather than amplification."

zero crossing point - The point at which a signal waveform crosses from being positive to negative or vice versa. This is the instant the signal has zero value, which makes it the spot where you want to make changes with the least amount of zipper (or other) noise, e.g., change gain in VCAs, or activate switches, transfer data, etc.

zero level or zero reference - The reference point used for setting audio signal levels throughout a sound system; usually +4 dBu for pro audio use; named for the original practice of using 0 dBm (then 0 dBu) as the reference level and even earlier using zero VU readings.

zeros - The roots of the numerator of a circuit transfer function, i.e., the values that make the numerator equal zero. Compare with poles.

zettahertz - Abbr. ZHz - One sextillion (1021) hertz.

Z-Fold® - Wire & Cable. Registered trademark of Belden for their unique cable that improves high frequency performance by reducing crosstalk between multipairs.

ZIF (zero insertion force socket) - A standard IC-socket design requiring the user to move a lever to insert or remove the chip -- as opposed to pressing and prying the chip manually -- hence, zero insertion force. The lever actuator (hopefully) eliminates damaging the IC pins.

ZigBee™ (formerly known as PURLnet, RF-Lite, Firefly, and HomeRF Lite.) - A low-cost, low-power, two-way, wireless communications standard between compliant devices anywhere in and around the home (automation, toys, PC peripherals, etc.), developed by Philips and others. Claiming lower cost, lower power consumption, higher density of nodes per network and simplicity of protocols, it is an alternative to Bluetooth. zipper noise - Audible steps that occur when a parameter is being varied in a digital audio processor, analog VCA, digitally-controlled attenuator, etc.

zirconium - Symbol Zr - A lustrous, grayish-white, strong, ductile metallic element obtained primarily from zircon and used chiefly in ceramic and refractory compounds, as an alloying agent, and in nuclear reactors as a highly corrosion-resistant alloy ( since it does not easily absorb neutrons). It is also used as a getter in vacuum tubes.

ZIT (Zappa Institute of Technology) (aka Zappa Tech) - School specializing in all aspects of live concert production, founded by Gail Zappa, wife of the legend.

Zizz - A whizzing or buzzing noise; esp. the noise made by the rapid motion of a wheel.

Zobel network or Zobel filter - [Also called Boucherot cell after Paul Boucherot who worked extensively with electrical networks and power.] 1. A filter designed according to image parameter techniques. 2. Audio amplifiers. Zobel networks are used in audio amplifiers to dampen out high frequency oscillations that might occur in the absence of loads at high frequencies. It is the commonly seen series resistor-capacitor combination located directly at the output of the driver stage, just before the output inductor (in analog power amplifiers). Typical values are 5-10 ohms in series with 0.1 microfarads. The network limits the rising impedance of a loudspeaker due to the speaker coil inductance. The output inductor found in most analog power amplifiers used to disconnect the load at high frequencies further aggravates this phenomenon. See Douglas Self's book for a good discussion of audio amplifier Zobel networks. 3. Loudspeakers. Some loudspeaker crossover designs include Zobel networks wired across the tweeter (high frequency) driver to compensate for the rise in impedance at high frequencies due to the inductance of the voice coil. The goal here is to try to keep the load seen by the crossover circuitry as resistive as possible. [After Dr. Zobel's paper appearing in the Bell Labs Journal: Zobel, O. J., "Theory and Design of Uniform and Composite Electric Wave Filters," Bell Sys. Tech. J., Vol. 2, pp. 1-46, Jan 1923.]

Zoetrope - (pronounced ZOH-uh-trohp) A kind of mechanical cinema invented in 1834 by William George Horner. It was an early form of motion picture projector consisting of a drum containing a set of still images turned in a circular fashion to create the illusion of motion. Horner originally called it the Daedatelum, but Pierre Desvignes, a French inventor, renamed his version of it the Zoetrope (from Greek word root zoo for animal life and trope for "things that turn.") Like other motion simulation devices, the Zoetrope depends on the fact that the human retina retains an image for about 100 milliseconds so that if a new image appears in that time, the sequence was seem to be uninterrupted and continuous. It also depends on what is referred to as the Phi phenomenon, which observes that humans try to make sense out of any sequence of impressions, continuously relating them to each other.

Zone - Separate and distinct listening locations within a complex sound system acoustically isolated from each other. A complex sound system is often broken up into zones with individual sound treatment for each.

zone of silence - "For a given source a region into which acoustic rays cannot penetrate; also known as a sound shadow. In outdoor sound propagation, upward refraction due to a decrease in temperature with height can combine with the ground to produce a zone of silence near the ground, beyond a certain radius from the source."

Zonophone - The name applied to the phonograph records and machines sold by founder Frank Seaman from 1899-1903. zoom microphone - Microphone analogy to the zoom lens. A design that allows synchronization with a zoom lens so that not only does the action get closer but the audio gets louder and focused. The trick is to make the microphone pickup pattern, or directivity, and sensitivity change from omnidirectional (wide-angle and wide soundstage) to supercardioid. At full zoom this makes the microphone very directional and is combined with higher preamp gain. This allows the audio and video to track in a realistic fashion.

z-plane - The complex plane in which the z-transform is represented.

Zt - Symbol for surface transfer impedance, the standard measurement used for quality rating of the RF shielding performance of cables, connectors and shield terminations. It measures how much voltage appears on the inner wires when the shield is driven by a strong RF signal and defines ZT as the induced voltage divided by the shield test current.

z-transform - A mathematical method used to relate coefficients of a digital filter to its frequency response, and to evaluate stability of the filter. It is equivalent to the Laplace transform of sampled data and is the building block of digital filters.

Zwicker, Eberhard - (1924-1990) German scientist who made significant contributions to the field of psychoacoustic masking and loudness perception.

Zwicker phons or Zwicker method or Zwicker loudness - A single-number scale for rating the loudness of complex sounds. It is based on a model that simulates the nonlinear operation of the human ear, in contrast to simple frequency-weighting such as A-weighting.

Zwicker tone - A psychoacoustic phenomena where subjects hear a "ghost" as an after tone when presented with a broadband noise source having a "gap," that is, a small band (say, a 1/3-octave band) missing. After the source stops, the subjects report hearing an afterimage centered in the missing gap.

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