Now looking at definitions starting with letter "x"
X-copy : An exact, 1:1 copy of audio and/or video material.
X-curveX-Curve : Transfer curve. See transfer characteristic.eXtended-Curve. As opposed to the Academy curve, the X-Curve is also known as the wide-range curve and is codified in ISO Bulletin 2969. Specifications call for pink noise, at listening position in a re-recording studio, or two-thirds of the way back in a theater, to be flat to 2kHz, rolling off at 3dB per octave after that. The small-room X-Curve is designed to be used in rooms with less than 150 cubic meters, or 5,300 square feet. This standard specifies flat response to 2kHz, rolling off 1.5dB per octave after that. Sometimes a modified small-room curve is used, starting the roll-off at 4kHz, rolling down 3dB thereafter.
X-track : Portions of production track that are split off into a separate unit or separate track on a workstation because they will be replaced by ADR.
X-Y or XY pair : See coincident pair.
X/Y function : Also called a Lissajous. Used to determine the phase of microphone set-ups, an X/Y function shows phase patterns on an oscilloscope. A mixer’s left output channel is connected to the X (vertical) input on the scope; the right output channel is connected to the Y (horizontal) input. If these two channels are panned center and are in- phase, they will show up on the scope as a diagonal line that moves up and to the right. If they are out-of-phase, the diagonal line will move down and to the right.
XG : A GM specification for MIDI instruments by Yamaha. XG instruments support reverb, chorus, and variation effects sends. Over 20 variation effects are available, including delay, flanging, phasing, rotary speaker simulation, distortion, and tremolo.
XLR : Xtended Locking Round. Developed by ITT/Cannon, XLRs are rugged, locking, multi-pin connectors frequently used in pro audio equipment. While 3-pin XLRs are most commonly seen on microphones and console inputs, other configurations also exist, such as 4-pin XLRs (a standard for stage intercom systems) and 5-pin XLRs (often used on stereo microphones). A designation of "M" after the pin number, such as "XLR-3M" indicates a male connector. Sometimes also called a Cannon connector.
XYZ controller : A 3-axis touch pad that transmits voltages based on finger position along the horizontal and vertical axes (X and Y) and aftertouch-type pressure (Z).