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auxiliary messages : A classification of MIDI messages which includes Active Sensing, All Notes Off, Local On/Off, and Reset, and which describes whether the particular MIDI device responds to any of thsese messages.

auto-assembly : In on-line editing, the process by which the edit-programmer produces the edited video master tape according to the instructions on the EDL, without human intervention. This is only possible where footage is consistently lit and exposed.

Automatic Volume Control /: See AVC.

automation : A system where manual control of a process is replaced or enhanced by computer control, such as mixing desk automation where faders, mutes, and equalization can be controlled in part or in whole by a computer. In write mode, the automation system produces a continuous record of all the actual fader settings and adjustments made by the engineer during a mix. Most systems allow changes on replay, while remembering and recreating previous manipulations of other tracks. The level changes are recorded and recreated by VCAs in each input module of the console. The VCA-produced data can be recorded directly onto a track of the multitrack tape, giving a continuous record of all mixdown fader settings. Or, the VCA outputs can be recorded onto a separate disk. In the latter system, alignment of the fader data with the multitrack master tape is achieve by referring to a common SMPTE timecodetime code recorded on the tape and disk systems. See mute mode, mute-write, null-point, read mode, snapshot automation, update mode, write mode.

attack time : (1) The rate of attack of a note. (2) The time it takes for a compressor or limiter to reduce its gain after a strong signal is applied to it. See release time.

audio coding mode : A parameter in Dolby Digital surround-sound format which refers to the number of channels and their location in for form F/R, where F is the number of front channels and R is the number of rear channels. For example, 5-channel surround is called 3/2 mode, stereo is 2/0, and mono is designated 1/0.

audio-to-MIDI : Software or hardware that takes a monophonic instrumental or vocal line, analyzes the pitches, amplitude, and timbre, and converts the line to MIDI notes, complete with pitch-bend, MIDI velocity and volume, and possibly additional controller data.

auditory masking : See frequency masking, masking.

Augmentation : (1) The increase of a major or perfect interval by one half-step to make an augmented interval. (2) The appearance of a musical idea in note durations which are longer than those used for its first appearance. This technique was often used in the ployphonic music of the middle ages and renaissance, as well as in contrapuntal music (e.g., fugues) of the baroque and later periods.

assemble editing : Editing of an audio or video program by making a master copy of the various takes, rather than physically splicing pieces of tape together. Virtually all digital editing is done this way. The opposite of insert editing.

atmospherics : See backgrounds.

assembly : See copyediting.

arrangement : (1) A version of a piece of music for resources other than those originally intended. This may be an instrumental version of a vocal number, a piano reduction of an orchestral piece, or may involve altering other parameters of the original, such as its harmony, rhythm, or structure. (2) In sequencers, a term sometimes used for the general layout of tracks, channels and patches, rather than a complete song. This template can often be saved as a separate file.

APRS Tape-Label System : The APRS has decided on a standard color-code for tape labelling:

Apple (�) menu : The main menu on a Mac, used to access system utilities (such as Keycaps), applications, files, and control panels. This is the equivalent of the Start menu on a PC-type system.

aperture time errors : In an A/D converter, the sample-and-hold circuit would ideally take zero time to determine the level of the signal waveform and to hold this level until the next sample is called for. However, it takes a finite time to charge the holding capacitor in the sample-and-hold circuit, and this is called the aperture time. Because the time required to establish a new value of charge depends on the amount of change in the signal level from one sample to the next, the aperture time will vary with the rate of change in signal level, increasing for high-level, high-frequency signals. The starting time of the sampling aperture is also slightly uncertain, and this is called jitter. In other words, lack of precision in the sampling time leads to amplitude errors in rapidly changing signals. The errors involve aperture time, uncertainty in aperture time, and jitter. The result is distortion of the sampled signal which rises with frequency.

compression : (1) The process of reducing the dynamic range of an audio signal by reducing the peaks so as to be able to boost the low levels. For every dB of compression applied, the S/N ratio is worsened by 1dB, assuming that the make-up gain is set so that the maximum levels of the compressed and uncompressed signals are the same, as the quieter parts of the original signal, plus any noise contained in these regions, will be raised in level. (2) A dynamic-range problem in loudspeakers caused by nonlinearity under conditions of high input power levels. At very high levels, the acoustic output increases more slowly or ceases to increase altogether as the input power increases, producing nonlinear distortion, i.e., a frequency response curve very different for very high levels. (3) Data compression used on digital audio files is a process ADPCM, MACE, for example. (4) The opposite of rarefaction whereby a quantity of data is reduced in order to occupy less storage space. See ATRAC.
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anti-imaging filter : See reconstruction filter.

anharmonic : See ="index.php?search=1&searchtxt=inharmonic">inharmonic.

anamorphic /: The camera/projector lens system which squeezes an image, usually originally in a 2:1 aspect ratio) onto film during shooting and "unsqueezes" it during projection. The resulting viewed image has an aspect ratio twice as wide as what was originally recorded on the film, e.g., if the image on the print is 2.2:1, the screen image will be 2.4:1. See also CinemaScope, flat(4), ‘scope.

AM suppression : The ability of an FM tuner or receiver to reject amplitude modulation of the received signal and be sensitive only to frequency modulation. Much of the interference and noise in broadcasting appears as amplitude modulation, so a tuner with good AM suppression will have less distortion and noise than a tuner with poorer suppression. Also called AM rejection.

amp/speaker simulator : A filter circuit that mimics the amplifier and loudspeaker voicing of an electric guitar and amplifier system.

Amplitude Modulation (AM) : The instantaneous amplitude modulation of one signal by another. This results in the formation of sidebands which contain the same information as the original signals, but translated upwards and downwards in frequency. In AM radio transmission, the audio signal is combined with a very high-frequency sine wave, called a carrier, in such a way that the amplitude of the carrier is varied in exact response to the amplitude and frequency of the signal. This is called the amplitude modulation of the carrier. The modulated carrier is transmitted at high power where it is received by radio sets that are tuned to the carrier frequency. The modulated carrier is then demodulated by a process called detection, recovering the original signal. In radio, a circuit that does amplitude modulation is also called a heterodyne.

amplitude errors : See frequency response errors, jitter.

amplitude : The relative strength (amount) of a signal, without regard to its frequency content. Amplitude is measured by determining the amount of fluctuation in air pressure (of a sound), voltage (of an electrical signal), or numerical data (in a digital application). When the signal is in the audio range, amplitude is perceived as loudness. Amplitude is the measurement of how much energy the sound has, i.e., the total change in air pressure during a single cycle of the sound wave. Amplitude, or sound pressure, is measured in a scale called decibels (dB). An increase of 3dB is equal to a doubling of a sound’s pressure. Amplitude can be expressed as either a negative or positive number, depending on the signals being compared. See also magnitude, SPL.

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