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Voice API for Windows Operating Systems Library Reference — November 2003 543
Glossary
A-law: Pulse Code Modulation (PCM) algorithm used in digitizing telephone audio signals in E-1 areas. See also
mu-law.
ADPCM (Adaptive Differential Pulse Code Modulation): A sophisticated compression algorithm for
digitizing audio that stores the differences between successive samples rather than the absolute value of each
sample. This method of digitization reduces storage requirements from 64 kilobits/second to as low as 24
kilobits/second.
ADSI (Analog Display Services Interface): A Bellcore standard defining a protocol for the flow of
information between a switch, a server, a voice mail system, a service bureau, or a similar device and a subscriber’s
telephone, PC, data terminal, or other communicating device with a screen. ADSI adds words to a system that
usually only uses touch tones. It displays information on a screen attached to a phone. ADSI’s signaling is DTMF
and standard Bell 202 modem signals from the service to a 202-modem-equipped phone.
AGC (Automatic Gain Control): An electronic circuit used to maintain the audio signal volume at a constant
level. AGC maintains nearly constant gain during voice signals, thereby avoiding distortion, and optimizes the
perceptual quality of voice signals by using a new method to process silence intervals (background noise).
analog: 1. A method of telephony transmission in which the signals from the source (for example, speech in a
human conversation) are converted into an electrical signal that varies continuously over a range of amplitude
values analogous to the original signals. 2. Not digital signaling. 3. Used to refer to applications that use loop start
signaling.
ANI (Automatic Number Identification): Identifies the phone number that is calling. Digits may arrive in
analog or digital form.
API (Application Programming Interface): A set of standard software interrupts, calls, and data formats that
application programs use to initiate contact with network services, mainframe communications programs, or other
program-to-program communications.
ASCIIZ string: A null-terminated string of ASCII characters.
asynchronous function: A function that allows program execution to continue without waiting for a task to
complete. To implement an asynchronous function, an application-defined event handler must be enabled to trap
and process the completed event. Contrast with synchronous function.
bit mask: A pattern which selects or ignores specific bits in a bit-mapped control or status field.
bitmap: An entity of data (byte or word) in which individual bits contain independent control or status
information.
board device: A board-level object that can be manipulated by a physical library. Board devices can be real
physical boards, such as a D/41JCT-LS, or virtual boards. See virtual board.