A-weighted, A-weighting@In measuring the intensity of a sound or noise source (for example, with a sound level meter), instead of merely adding the power of all audio frequency components to derive a sum, the powers of different frequency components are usually "weighted" before adding (in other words, some frequency ranges count less than others). This can be done according to several curves. The most common is the "A" weighting, which reflects the human ear's relative lack of sensitivity to the low and high extremes of the audible frequency range, particularly at SPL levels less than about 55 dB. The A Weighting is therefor more useful than "B" or "C", for measuring the low-level sounds like background noise. See also Equal-Loudness Contours, Phon.@A/B Roll Edit@Video term. Video editing process where two video playback transports (A and B) are synchronized through SMPTE TimeCode and Video Sync (genlock), under the control of a video editing console (edit controller). Dissolves, wipes and other video effects can be created using the video signals coming from the two machines, while recording to a third machine during the edit assembly process.@A/D Converter@Same as ADC (Analog to Digital Converter, a device which converts a continuous input waveform into a series of binary numbers). See definition.@A/D/A, ADAC@Analog-Digital-Analog (Conversion). Refers to the entire conversion process of audio from the analog domain into digital data, and then back into an analog signal. See DAC, ADC, Sampling, Digital.@A/ROSE@Apple Realtime Operating System Extension. Enhancement to the Macintosh operating system formerly used by programmers to intercept instructions sent to Macintosh hardware components by certain programs, redirecting them to different hardware. Consisted of a single "Extension" file. For users of Pro Tools I (the original, now known as 442), A/ROSE was obligatory for systems with a System Accelerator card (also SysAxe, an A/ROSE-compatible Extension file). On these 442 systems, playback and recording of audio files in the Pro Tools program, normally directed to disks connected to the Mac's own SCSI port, was re-directed through the System Accelerator card, which featured a high-speed SCSI controller and SCSI port (where hard disks used for audio were connected). See also Extension, System Acclerator.@Access Time@The time it takes a disk (or any other storage medium) to make information available for retrieval by a computer. For disk drives, Access Time is determined by two factors. First, the average interval of time it takes for the read/write heads to be physically moved to the track where a desired file is located (Seek Time). Second, a shorter interval (Latency, as much as 8 milliseconds) which is the average amount of time it takes for the appropriate sectors on the rotating disk surface to pass under the head. (For digital audio and video applications, note that Access Time does not indicate how rapidly the unit will actually retrieve data, once it has begun to read the desired file. This is described by the device's Sustained Transfer Rate (usually in MB/sec.). We must know BOTH Access Time and Sustained Transfer Rate to get a general idea of the total average Throughput of a disk drive.) See also Seek Time, Transfer Rate, Throughput.@ACM, Audio Compression Manager@Format developed by Microsoft as the standard interface for data compression and digital signal processing (DSP) of files containing audio data in the Windows environment, particularly files in the .WAV format. Certain PC audio editing programs such as Sound Forge allow users to create their own ACM digital signal processing routines.@Active Sensing@A MIDI message (of the type "System Real Time"). Active Sensing messages can be sent periodically (about three times a second), they are used as a verification to the receiving device that the MIDI line is still functioning. Transmittal Active Sensing data is not mandatory; however it is an option in many software MIDI sequencers. Active Sensing can also cause problems, triggering false MIDI events in certain older MIDI modules; in fact it is falling into disuse. In general, if you don't have a specific need, it is better not to activate Active Sensing, especially if you are transmitting large volumes of MIDI data which might already cause "log jams" or delays.@Active Termination (SCSI)@Computing term. A function of some SCSI devices (such as disk or tape drives), by which the device senses its physical position in the SCSI chain. If the device is at the external end of the SCSI chain, it automatically switches in the appropriate resistor to eliminate reflections in the SCSI Bus. (Note: drive controllers used by some resellers put the active termination function under the control of a digital processor, for instance "DA Term" by APS Technologies.) See also SCSI , SCSI Terminator.@ADAC@Analog-Digital-Analog Converter. See A/D, D/A.@ADAT@The ADAT is an 8-channel digital audio recorder developed by Alesis Corporation. It records audio at a default sampling rate of 48 kHz, 20-bit resolution (16-bit on original models), using a 1/2" inch SVHS video tape as the storage medium. The ADAT also features a proprietary optical interface for the transfer of 8 channels of digital audio (also known as ADAT Optical or "Lightpipe"), which is supported by various manufacturers of synthesizers, digital audio workstations, and signal processors. It is an example of an MDM, a Modular Digital Multitrack, as are the Tascam DA-88 (Hi-8 competitor of the ADAT) and ADAT-compatibles from Fostex (RD-8) and Panasonic; multiple machines can be interconnected, for 16, 24, 32 tracks, etc. Includes the LRC, Little Remote Control; optionally the BRC, Big Remote Control, offers more sophisticated editing functions and LTC synchronization. Several DAW manufacturers offer interfaces that enable digital audio transfer between the hard-disk recording system and ADAT.@ADB@Apple Desktop Bus. A connection system developed by Apple Computer for the Macintosh and Apple IIGS, used for connecting keyboards, mouse, graphics tablets, hardware copy protection keys (a.k.a. "dongles"), etc. to the computer. Macs and PowerMac traditionally had one or two ADB connectors, known as "ports", on the back of the computer. The ADB cable to the alphanumeric keyboard could be connected here; the keyboard also featured a second ADB port where a mouse or other device could be "daisy chained" (strung together in a linear fashion) along the ADB bus which extended from this same port. Newer Macintosh models use USB (see definition) to connect keyboards, pointing devices and other peripherals.@ADC, Analog-to-Digital Converter@A circuit or hardware peripheral that converts the continuously varying voltages of an input signal (analog) into a series of binary numbers (digital). These binary numbers represent "samples" (measurements) of the input voltage taken at regular time intervals. See also Quantization, Digital, Sampling, Aliasing.@Additive Synthesis@A method of electronic sound creation where complex timbres are created by combining simpler waveforms (especially Sine Waves); "partials" whose pitch and amplitude envelopes can be individually controlled, to create changing contours of spectral content and loudness over the duration of each note.@Address Track@A type of timecode used only on 3/4" professional video recorders (U-Matic, 3/4U). The SMPTE timecode information is incorporated longitudinally into the same area of the tape as the video signal. Like VITC TimeCode (see definition), address track timecode offers the advantage of not using either of the two audio tracks provided by the 3/4U format. See VITC, SMPTE, U-Matic.@Adobe Premiere@Video editing software for Macintosh and PC, supporting up to 99 QuickTime movie tracks and 99 AIFF audio tracks, video transitions, titles, transparencies, also supports EDL formats and SMPTE. Windows version supports AVI digital video file format. Accepts audio processing plug-in software such as Waves' Q2, and InVision's CyberSound FX, along with many other image processing "plug-ins" similar to Adobe Photoshop plug-in filters. See also QuickTime, AIFF.@ADPCM@Adaptive Delta Pulse Code Modulation. A data compression method for digital audio data. ADPCM is utilized to compress audio data on CD-I discs, where the sampling rate can also be reduced to 37.8 kHz or 18.9 kHz, according to quality level selected. ADPCM also uses companding, as well as frequency-selective bit-depth reduction, in order to achieve dramatic reductions in the size of audio data. See also CD-I.@ADR, Automated Dialog Replacement@The process of replacing actors' lines, that were recorded live during the film or video shoot, with higher-quality studio takes. In traditional ADR, three loops of film are mechanically synchronized on separate transports. The first film loop contains the recorded images, projected for the actors so that they can maintain lip sync. The other two film loops are magnetically striped for audio recording. One contains the original audio track, while replacement audio is recorded on the other. An "ADR Cue Sheet" is prepared by the ADR Editor, where characters, their lines of dialog, and start/stop times (SMPTE or Feet & Frames) for each are listed. These time references indicate the correct beginning and end of audio recording, for every line of dialog spoken by each actor. This data is then introduced into a computer, which controls the three film transports, and automatically activates audio recording at the appropriate times. The ADR system gives the actor three audible beeps (at 3, 2, and 1 feet) before the start of each line to be recorded. ADR can also be done using ordinary audio recorders synchronized through SMPTE, and increasingly with non-linear digital audio editing systems. However the ADR process implies this very specific working style, known throughout the industry as Looping. (Not to be confused with the Loops of audio used on digital samplers!)@ADSR@Abbreviation for Attack, Decay, Sustain, Release; the four stages of the traditional Envelope Generator, found on many synthesizers (also the standard method of describing the loudness contour ofacoustical sound sources). See also Envelope, Envelope Generator.@AES@Audio Engineering Society. A professional association of sound engineers headquartered in New York, with local chapters worldwide. The AES sponsors technology symposiums, and large annual conventions where manufacturers often introduce new audio products.@AES/EBU@Digital audio transfer standard developed jointly by the Audio Engineering Society (AES) and the European Broadcast Union (EBU). Format for digital interchange of 2-channel audio, at up to 24-bit resolution, along with timing information and other data relating to sample rate, etc. Audio data and subcode information are transmitted in 192-bit blocks of data, each composed of 24 eight-bit words. AES/EBU interfaces use balanced XLR connectors (2 conductors plus shield), permitting longer cable lengths than S/PDIF. (Up to 328 feet/100 meters, although most manufactures recommend less than 30 meters. Use of 110-Ohm cable is HIGHLY recommended.) AES/EBU is somewhat more stable than the consumer-oriented S/PDIF digital connection, and does not incorporate SCMS copy protection. It should be used for any digital cable connections that exceed about 15 feet. See also S/PDIF, SCMS.@AFL@After-Fade Listen. On mixing consoles (or similar software constructs), describes a solo function which is post-fader (instead of the more common "pre-fader" solo). See also PFL, Solo.@Aftertouch, Channel Pressure@MIDI continuous control message derived from the amount of pressure applied to the entire keyboard, after keys have been depressed; its values range from 0 to 127. Aftertouch (Channel Pressure) is more commonly found on keyboard controllers than Poly Pressure, which is more expensive to implement. With Aftertouch, the entire keyboard triggers a common stream of aftertouch values that affect the entire MIDI channel, whereas Poly Pressure sends a separate stream of aftertouch values for each key, consequently generating a greater volume of MIDI data. See also Poly Pressure.@AGC, Automatic Gain Control@A circuit which assists in maintaining consistent levels in audio recordings, especially common on the audio inputs of video recorders and low-end cassette recorders. AGC circuits lower the record level when higher input signal levels are detected, and gradually raise the record level when the input signal strength is weaker. Although many professional video recorders incorporate AGC circuits, most professionals avoid using them, as they produce undesirable side effects in the audio. (For example, loud sounds cause sudden drops in record level which still aren't fast enough to avoid the initial distortion; then long, quiet sections cause the record level to gradually rise, making Room Tone and background noise all that more apparent.) See also Dynamics Processing, Compressor, Limiter, Noise Gate, Expander, Gain.@AIFC@Audio Interchange File, Compressed. An AIFF digital audio file, to which data compression has been applied. See AIFF.@AIFF@An audio file format (Audio Interchange File Format) useful for exchanging either high- or low-resolution digital audio between different programs or computers. The AIFF format does not include Sound Designer-style region names within an audio file, but it does permit up to 20 loops in a file. This file format is particularly common in the Apple QuickTime environment, and also in some CD-ROM sound libraries, such as Sound Ideas.@Alert Box@Apple Macintosh term. A small window which appears on the screen, communicating messages from the system or current program; the only possible response to an Alert Box message is to press the "OK" button. See also Dialog Box.@Algorithm@A set of instructions or rules used to solve a particular type of problem, or complete a given kind of calculation, in a prescribed number of steps. For example, an algorithm may provide the instructions for a specific type of signal processing in an effects unit, or for generating a sound in a synthesizer. In algorithmic composition, algorithms are used to generate specific permutations of the musical data (usually MIDI) introduced by the performer or composer. Specialized MIDI programs exist for this application.@Alias@1. Apple Macintosh term. A convenient feature introduced in the Macintosh Operating System, version 7. An Alias is a "dummy" icon which can be created for an existing program, file, folder or disk; it can be dragged to a different location than the original. Clicking on this "alias" is the same as clicking on the original item. Aliases can be conveniently grouped together for frequently accessed items, which might otherwise require navigation of numerous nested levels of folders and disks in order to reach the desired item. Aliases can also be dragged to the "Apple Menu Items" folder, so that frequently used programs and documents can appear as selections within this menu. "Shortcuts" in the Windows environment are roughly equivalent to an Alias.
2. Emagic Logic Audio term. Double of an object which does not contain any data itself but just refers to the data of the original. An alias is equivalent to a "short-cut" in Windows 95/98.@Aliasing@Noise in the form of undesirable false signal components that can be generated during incorrectly-implemented analog-to-digital conversion processes. Occurs when the Sampling Frequency of a digital system is less than twice the highest frequency contained in the signal that the system attempts to digitize (record). Aliasing artifacts are avoided through the use of brickwall anti-aliasing lowpass filters at the input, which eliminate all frequency components over half the sample rate, often in conjunction with oversampling methods which reduce unwanted coloration from the anti-aliasing filters themselves. For a familiar example of aliasing, consider the wagon wheels in a western movie, which when rolling sometimes appear to rotate backwards. This illusion is a result of the interaction between the wheel's speed of rotation and the film's frame rate. See also Nyquist Theorem, Sample Rate.@All Notes Off@A System Common MIDI message that turns off all notes currently sounding, useful for silencing stuck notes on synthesizers (it happens!). Can also be inserted as a command in a MIDI sequence to ensure that all notes are in the off position before sending additional MIDI data. All Notes Off messages may also be sent when the user hits Stop on a sequencer's transport. See Panic Button.@Allocated Blocksize@Computing term. A variable in the formatting of a hard disk. Concentric data "tracks" which are created for magnetic storage of digital data by the process of formatting (also known as initialization), are subdivided into sectors, which in turn are subdivided into Blocks. The number of blocks per sector can be varied; a smaller number of blocks per sector may increase access speed to the disk. However, since an entire block is allocated for data, even if only a small portion of it is actually used, use of less blocks per sector may make inefficient use of disk space. See also Format, Access Time.@Allocator@A utility program provided by Digidesign to users of TDM-equipped Pro Tools systems, which graphically displays the current utilization of the DSP chips on the Mix Farm (or DSP Farm) card(s). Assists in managing the DSP hardware resources assigned to various plug-in modules in the TDM environment. See also Mix Farm, DSP Farm, TDM.@Alpha Channel@In computer graphics, and electronic video post-production, the alpha channel is an additional channel (besides the Red, Green, and Blue channels, RGB), which carries processing information. This may be luminance or chroma transparency, a video keym edge enhancement information, etc., the alpha channel is thus particularly useful for compositing together multiple source images.@AMII, AMIII@Abbreviation for Audiomedia II/III, digital audio recording and processing cards for Macintosh computers (and also Windows, in the case of AMIII). The AMII is now discontinued - it was replaced by the AMIII. See Audiomedia II.@Amplifier@A device that tracks the amplitude of an incoming signal, increasing the strength of the signal by a specific input/output ratio, by adding power from another source. (In other words, an amplifier applies a "gain change" to the input signal.) The amplifier's Transfer Function describes the magnitude of the output signal, as compared to the input signal.@Amplitude@The height of a waveform; for audio greater amplitudes correspond to greater signal strengths or loudness. In technical terms, amplitude is the magnitude, or level of variation away from the zero value, in an electrical signal or acoustical sound wave (i.e., the range of variations in voltage levels or air displacement caused by that periodic waveform). Greater amplitudes represent more intense electrical signal, pressure variation, or air displacement. In other words, for music and audio, louder sounds have relatively greater amplitudes. (For instance, the vibrations produced by a louder version of a sound wave actually cause air molecules to oscillate back and forth through greater distances.) Acoustic amplitudes (sound pressure levels) are measured in decibels, or dB, see definition. To be meaningful, any figures cited for amplitude must also specify the measurement method, peak, rms, instantaneous, maximum, etc.@Amplitude Modulation, AM@Alteration of a signal by varying (modulating) the level (amplitude) of that signal according to some other reference. Some analog synthesizers electronically modulate a carrier waveformÕs amplitude with a higher frequency modulator signal, creating sum and difference frequencies which produce a new, more complex waveform. AM radio transmissions are based on similar principles. Another simple application of AM is the creation of a tremolo effect, through the use of a low-frequency oscillator as a source for modulating the volume of another sound.@Analog@Term derived from "analogous", which means "similar to". Analog processes record or monitor events in a continuous way, converting them into similarly continuous mechanical or electronic representations of the original phenomenon. In analog audio and video recording, a signal is stored as a continuously varying electrical or mechanical representation (analog) of the input signal, for instance on magnetic tape or a phonograph record. Analog synthesis uses electronic oscillators, filters, amplifiers and envelope generators to directly create and manipulate electrical voltages; their values can be continuously varied throughout their range. In contrast, the values recorded by digital systems, or the control values used in digital synthesis, are discrete numerical values, which approximate the corresponding analog amplitudes. See also Digital, Oscillator, Filter, Envelope.@Anti-Aliasing Filter@A component found at the input stage of an Analog-to-Digital Converter (ADC). It performs low-pass filtering on the input signal before it reaches the Sample & Hold circuit and digitizing process. The Anti-Aliasing filter prevents frequencies higher than half (1/2) the sampling rate from reaching the audio digitizing circuitry, in order to avoid the creation of false, "alias" frequency components which can be caused by the inaccurate capture of high-frequency input waveforms. See Aliasing, Nyquist Theorem, Sample Rate, Quantization, Lowpass Filter, ADC.@Anti-Imaging Filter@A component found following the DAC (Digital-to-Analog Converter) in digital audio systems. Basically a low-pass filter, with a very steep slope of attenuation ("brickwall") beyond its Cutoff Frequency (which is somewhat lower than the Nyquist Frequency, of the system, equal to 1/2 the Sample Rate. This filter eliminates undesirable high-frequency artifacts produced by the digitization process, including "images" of the original audio frequency spectrum at multiples of the sample rate, and also the stair-step shape introduced into the waveform by the process of Quantization itself.) See Quantization, DAC.@
