n. A class of compression encoding and decoding algorithms used in audio compression and other data compression applications. These algorithms store digitally sampled signals as a series of changes in value, adapting the range of the change with each sample as needed, thus increasing the effective bit resolution of the data. See also pulse code modulation. Compare adaptive differential pulse code modulation. Acronym: ADPCM.

AVI

n. Acronym for Audio Video Interleaved. A Windows multimedia file format for sound and moving pictures that uses the Microsoft RIFF (Resource Interchange File Format) specification.

codec

n. 1. Short for coder/decoder. Hardware that can convert audio or video signals between analog and digital forms. 2. Short for compressor/decompressor. Hardware or software that can compress and uncompress audio or video data. See also compress2, uncompress. 3. Hardware that combines the functions of definitions 1 and 2.

MIDI

n. Acronym for Musical Instrument Digital Interface. A serial interface standard that allows for the connection of music synthesizers, musical instruments, and computers. The MIDI standard is based partly on hardware and partly on a description of the way in which music and sound are encoded and communicated between MIDI devices. The information transmitted between MIDI devices is in a form called a MIDI message, which encodes aspects of sound such as pitch and volume as 8-bit bytes of digital information. MIDI devices can be used for creating, recording, and playing back music. Using MIDI, computers, synthesizers, and sequencers can communicate with each other, either keeping time or actually controlling the music created by other connected equipment. See also synthesizer.

MULTIMEDIA

n. The combination of sound, graphics, animation, and video. In the world of computers, multimedia is a subset of hypermedia, which combines the aforementioned elements with hypertext. See also hypermedia, hypertext.

hypermedia
n. The integration of any combination of text, graphics, sound, and video into a primarily associative system of information storage and retrieval in which users jump from subject to related subject in searching for information. Hypermedia attempts to offer a working and learning environment that parallels human thinking--that is, one in which the user can make associations between topics, rather than move sequentially from one to the next, as in an alphabetic list. For example, a hypermedia presentation on navigation might include links to astronomy, bird migration, geography, satellites, and radar. If the information is primarily in text form, it is regarded as hypertext; if video, music, animation, or other elements are included, the information is regarded as hypermedia. See also hypertext.

MPEG

n. 1. Acronym for Moving Pictures Experts Group. A set of standards for audio and video compression established by the Joint ISO/IEC Technical Committee on Information Technology. The MPEG standard has different types that have been designed to work in different situations. Compare Motion JPEG. 2. A video/audio file in the MPEG format. Such files generally have the extension .mpg. See also JPEG. Compare Motion JPEG.

MPEG-1

n. The original MPEG standard for storing and retrieving video and audio information, designed for CD-ROM technology. MPEG-1 defines a medium bandwidth of up to 1.5 Mb/s, two audio channels, and noninterlaced video. See also MPEG (definition 1). Compare MPEG-2, MPEG-3, MPEG-4.

MPEG-2

n. An extension of the MPEG-1 standard designed for broadcast television, including HDTV. MPEG-2 defines a higher bandwidth of up to 40 Mb/s, five audio channels, a wider range of frame sizes and interlaced video. See also HDTV, MPEG (definition 1). Compare MPEG-1, MPEG-3, MPEG-4.

MPEG-3

n. Initially an MPEG standard designed for HDTV (high-definition television), but it was found that MPEG-2 could be used instead. Therefore, this standard no longer exists. See also HDTV, MPEG (definition 1). Compare MPEG-1, MPEG-2, MPEG-4.

MPEG-4

n. A standard currently under development designed for videophones and multimedia applications. MPEG-4 provides a lower bandwidth of up to 64 Kb/s. See also MPEG (definition 1). Compare MPEG-1, MPEG-2, MPEG-3.

pulse code modulation

n. A method of encoding information in a signal by varying the amplitude of pulses. Unlike pulse amplitude modulation (PAM), in which pulse amplitude can vary continuously, pulse code modulation limits pulse amplitudes to several predefined values. Because the signal is discrete, or digital, rather than analog, pulse code modulation is more immune to noise than PAM. Compare pulse amplitude modulation, pulse duration modulation, pulse position modulation. Acronym: PCM.

QuickTime

n. The multimedia extensions to the Apple Macintosh System 7 software, also available for Windows. QuickTime can synchronize up to 32 tracks of sounds, video images, or MIDI or other control output.

RealAudio

n. Web software that streams prerecorded or live audio to a client, such as a Web browser, by decompressing it on the fly so that it can be played back to the Web browser user in real time.

sampling

vb. 1. In statistics, gathering data from a representative subset of a larger group (called a population)--for example, determining a country's presumed voting pattern by polling a demographic cross section of voters. Other uses of this type of sampling might include checking the accuracy and efficiency of computerized transactions by reviewing every hundredth transaction or predicting traffic volumes by measuring traffic flow in a few strategic streets. There are many statistical procedures for estimating how accurately a given sample reflects the behavior of a group as a whole. 2. The conversion of analog signals to a digital format; samples are taken at periodic intervals to measure and record some parameter, such as a signal from a temperature sensor or a microphone. Analog-to-digital converters are used in computers to sample analog signals as voltages and convert them to the binary form a computer can process. The two primary characteristics of this type of sampling are the sampling rate (usually expressed in samples per second) and the sampling precision (expressed in bits; 8-bit samples, for instance, can measure an input voltage accurate to 1/256 of the measured range).

sampling rate

n. The frequency with which samples of a physical variable, such as sound, are taken. The higher the sampling rate (that is, the more samples taken per unit of time), the more closely the digitized result resembles the original. See also sampling (definition 2).

WAV

n. A file format in which Windows stores sounds as waveforms. Such files have the extension .wav. Depending on the sampling frequency, on whether the sound is monaural or stereo, and on whether 8 or 16 bits are used for each sample, one minute of sound can occupy as little as 644 kilobytes or as much as 27 megabytes of storage. See also sampling (definition 2), waveform.
 

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