ModemSpy: record phone conversations to MP3

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COMPUTER TELEPHONY GLOSSARY

64 kbps

64 kilobits per second data rate. The rate of data transmission on a single channel of E1, T1, etc. Data storage at 64kbps is usually a verbatim copy of the signal on the stream, although it is possible to convert from A-law to Mu-law, remaining at 64kbps but modifying the binary data.

32 kbps

32 kilobits per second data rate OKI ADPCM and G.721/G.726 ADPCM effectively use 4 bit code words for each signal sample. This uses half the amount of data as A-law and mu -law to describe the speech signal.

24 kbps

24 kilobits per second data rate. This data rate is either OKI ADPCM (4 bits per sample) sampled at 6kHz, OR G.726 in a mode using 3 bits per sample.

16 kbps

16 kilobits per second data rate. Prosody uses a proprietary data compression algorithm which encodes speech at 16kbps, a quarter of the data rate of G.711.

12 kbps

12 kilobits per second data rate.Prosody uses a low quality data compression algorithm which encodes speech at 12kbps.

8 kbps

8 kilobits per second data rate. Prosody supports a proprietary high quality CELP algorithm, which records speech using 1/8th of the data rate of G.711

ADPCM

Adaptive Differential PCM: A variant of PCM, in which each code word corresponds to the difference between the signal level and an internally predicted value for the signal level. The scaling of the code word is adapted based on signal history, as is the logic for making signal level predictions.

A-law

G.711 A form of PCM, whereby the code word maps non-linearly to the signal value. A-law code words are 8 bits wide. Used for the B-channel in ISDN.

algorithm

In general, a set of rules, usually followed by a computer. A process implemented in software, e.g. 16kbps data compression.

API

Application Programmer Interface: The set of function calls used by a programming language such as C, to access and operate the hardware product. e.g. call_openin(), sm_play_wav_file()

ASR

Automatic Speech Recognition An algorithm running on a computer telephony platform such as Prosody which recognises spoken words.

Audiotex

An automated system which transmits recorded speech over the telephone, usually a Premium Rate service.

Barge-in

In ASR, barge in refers to the user speaking while the system is issuing an outgoing prompt.

Basic rate (BRI)

A digital telephony trunk carrying two 64kbps B-channels and one 16kbps D-channel. Also referred to as ISDN-2

B-channel

Bearer Channel In digital telephony, the channel which carries the subscriber&s information - usually speech, but possibly modulated data (e.g. fax) or raw data (e.g. V.110)

BONDING

Bandwidth on Demand A single telephone call that uses of a number of 64kbps B-channels to provide bandwidth for a call that uses higher bit-rates. Without BONDING, transfer of this data would require a number of separate calls to provide the bandwidth.

Cadence

The on / off sequence of a tone or set of tones. Different call-progress tones often share the same pitch of tones, but have different cadences.

Call-Progress tones

Specifically, tones generated on a telephony channel to indicate the status of a telephone call, e.g. Path Engaged, Ring Tone. Generally, the term is used for any tone which is specified by pitch and cadence.

CELP

Code-Excited Linear Prediction Whereas PCM and ADPCM encode each sample of speech using an integer (together with linear prediction), CELP algorithms encode short sequences of samples with a single symbol. The symbol indexes into a codebook of potential sequences, which is known to the encoder and decoder.

CCITT

Consultative Committee on International Telegraph and Telephone The standards body for the telephony industry, now replaced by the ITU.

channel

The carrier of a single (speech or data) signal. Can be simplex or duplex

Codec

coder - decoder A pair of algorithms for encoding and subsequently decoding a signal, e.g. a speech signal at 8kbps

Conference

Broadly, the addition of two or more speech signals onto one channel. In a teleconference, the signal transmitted to each listener is the sum of the speech from the other parties.

Connected-Word Recognition

Automatic speech recognition (ASR) which allows the speaker to say words without spaces in between. Connected word recognisers tolerate co-articulation (e.g. "Two Eight" becomes "Tooweit")

CRC

Cyclic Redundancy Check A method for verifying the integrity of a block of stored or transmitted data.

CTI

CTI stands for Computer Telephony Integration. It involves integrating computer systems with telephony resources to augment the capabilities of a call center.

Cut-through

A DTMF detector must be able to detect DTMF tones in the presence of other interfering signals.

D-channel

Data channel: In digital telephony, a channel which carries signalling information for use by the telephone network.

Data Compression

An algorithm which allows a signal to be stored in a more compact form than its original, "raw" format.

Device Driver

The software that provides communication with specialised hardware. A software application accesses the device driver via its API

DSP

Digital Signal Processing: The manipulation or analysis of any signal (such as sound, pictures, radio waves) by a digital computer.

DTMF

Dual Tone, Multi-Frequency. The set of dual tones generated by a typical "touch-tone" telephone keypad.

duplex

A duplex channel carries a signal in both directions between two points. A full duplex channel can transmit in both directions simultaneously, whereas a half-duplex channel alternates between directions. A full duplex channel is effectively two channels, whereas a half-duplex channel alternates direction.

full duplex

A duplex channel carries a signal in both directions between two points. A full duplex channel can transmit in both directions simultaneously, whereas a half-duplex channel alternates between directions. A full duplex channel is effectively two channels, whereas a half-duplex channel alternates direction.

half duplex

A duplex channel carries a signal in both directions between two points. A full duplex channel can transmit in both directions simultaneously, whereas a half-duplex channel alternates between directions. A full duplex channel is effectively two channels, whereas a half-duplex channel alternates direction.

Echo Cancellation

Elimination of side-tone from a return signal. The transmitted signal is used as a reference.

File

A lump of data stored in a computer. The data may be an executable program, text, information readable by the computer, speech, etc.

Fixed point

Arithmetic which uses only integers. The integers usually represent multiples of an independent scaling factor. The scaling must be handled separately by extra logic.

Floating point

Numbers are stored as an integer and an explicit scaling factor. Scaling is handled by the Floating Point Unit.

G.711

See A-law and m-law

G.721

An ITU standard for compression of speech signals to 32kbps, 48kbps or 24kbps. Now obsolete, but replaced by G.726

G.723.1

Otherwise known as TrueSpeech, a method for compressing speech signals to a data rate of 7.6kbps. Used extensively in internet telephony (VoIP)

G.726

An ITU standard for compression of speech signals to 32kbps, 48kbps, 24kbps or 16kbps. Replaces G.721

Gain

A multiplier applied to a signal. Usually refers to volume level. Measured in dB.

Grunt Detection

Detection of any significant signal on a telephone line. Prosody&s grunt detection estimates background noise, and provides the application with the duration and average energy of the "grunt"

GSM6.10

The method of speech data compression used in the GSM mobile telephone system.

H.320

ITU standard for transmitting video on narrowband telephony channels

Hidden Markov Model (HMM)

A mathematical tool used to describe statistics of a changing, unknown system based on observations of the effects of that system. In Automatic speech recognition, an abstract statistical model of the "speech" is generated, based on acoustic observations.

ISA

Industry Standard Architecture Similar to IBM-AT, a standard bus for connecting peripheral hardware to a Personal Computer main board.

ISDN

Integrated Services Digital Network A switched network providing end-to-end digital connectivity for simultaneous transmission of voice and/or data over multiple multiplexed communications channels and employing transmission and out-of-band signalling protocols that conform to internationally defined standards. An ISDN line consists of a collection of B-channels carrying speech and/or data, and one or more D-channelscarrying signalling information.

ISDN-2

see Basic Rate

IVR

Interactive Voice Response An IVR system communicates with a user using spoken prompts. The user can control the system using either DTMF or pulse dialled digits, or a restricted set of spoken words (ASR).

Isolated Word Recognition (IWR)

Automatic speech recognition (ASR) which requires the speaker to annunciate single words with spaces inbetween

ITU

International Telecommunications Union: Official body for ratifying standards in telecommunications.

Mark or Space

When describing a signal which periodically alternates between the on state and the off state, the "mark" is the amount of time on, and the "space" is the amount of time off.

MFLOPS

Mega Floating-point Operations Per Second: A measure of the power of a floating point processor. Since many processors allow parallel floating point operations, this is often larger than the number of MIPS (million instructions per second)

Modem

Modulator -Demodulator A device or algorithm which converts data into a signal which can be borne on a telephone line (either as an analogue signal or on the B-channel in digital telephony) and subsequently converts this signal back to data.

µ-law (mu-law)

G.711 An alternative to A-lawPCM, used for the B-channel of T1 streams.

MVIP

Multi Vendor Integrated Protocol An industry standard for connecting PC-based computer telephony hardware.

OKI ADPCM

An efficient, low quality version of ADPCM made popular by OKI, and now an industry standard. The scaling of the code integer is adapted but there is no adaptive predictor.

Operating System

In a computer, the "system" or "executive" software, which oversees all other "user" programs that perform specific tasks.

PCI

Peripheral Component Interconnect: An alternative to ISA bus for connecting peripheral hardware to a Personal Computer main board. PCI allows much faster data exchange than ISA and allows much of the device configuration to be completed in software.ISA and allows much of the device configuration to be done in software.

PCM

Pulse Code Modulation: A method of describing a time-varying signal using a sequence discrete integers as code words. Each integer code word describes the signal level at a point in time.

Premium Rate

A telephone line or number with an increased tariff which provides revenue for both the telecommunications provider (PTT) and the owner of the telephone line. Information or entertainment services are often provided using premium rate lines.

Primary Rate

A digital telephony trunk carrying 30 64kbps B-channels and two 64kbps D-channels

Prosody

The powerful and versatile speech processing card from Aculab.

Pulse detection

In the absence of DTMF capability, telephones dial by repeatedly switching a current on the line. This is done at a rate of approximately ten switches per second. The switching current does not propagate beyond the local exchange and so is very difficult to detect accurately by a remote system. This method of dialing is used by all rotary dial telephones.

Pulse dialling

In the absence of DTMF capability, telephones dial by repeatedly switching a current on the line. This is done at a rate of approximately ten switches per second. The switching current does not propagate beyond the local exchange and so is very difficult to detect accurately by a remote system. This method of dialing is used by all rotary dial telephones.

10pps detection

In the absence of DTMF capability, telephones dial by repeatedly switching a current on the line. This is done at a rate of approximately ten switches per second. The switching current does not propagate beyond the local exchange and so is very difficult to detect accurately by a remote system. This method of dialing is used by all rotary dial telephones.

PSTN

Public Services Telepone Network: The telephone network that the public connect to! e.g. BT, NTL, Cable London. Your analogue or ISDN line connects to such a network. It enables you to connect to anyone in the world! via a telephone connection.

Q.25

An ITU specification for DTMF tones. Recursive.

SCBUS

Dialogic equivalent of MVIP

SHARC

ADSP-2106x Analog Devices& floating point Digital Signal Processor chip

Side-tone

The fraction of an outgoing signal which is reflected by an analogue telephone.

Simplex

A channel which allows transmission in one direction only, for example terrestrial radio. All digital telephony channels are simplex; a duplexconnection is provided by a pair of channels.

Stream

A collection of 64 kbps digital signals, time-division multiplexed onto one physical transmission line. For example, a single MVIP stream carries 32 x 64 kbps signals, each of which is referred to by its timeslot.

Switch

In the context of computer telephony, switching is the connection of a speech channel to a resource, or to the MVIP or SC bus.

T-1

A digital telephony trunk providing 24 64 kbpschannels. In Robbed-bit T-1, the D-channel is buried within the B-channels, using least-significant bits. Otherwise, T1 provides 23 B-channels and 1 D-channel. In talk-off, Mitel, Bellcore a DTMF detector can sometimes detect valid tones in a speech signal, due to frequency components of the signal lying in the same range as valid DTMF tones. This false detection is "talk-off". There are two standard tapes of signals used to measure talk-off performance, respectively by Mitel and Bellcore.

TTS

Text to Speech A system which converts text to spoken language.

Time slot

The sub-division of a stream which carries one channel of information.

Trans-coding

Conversion of one recorded speech format to another, for example, conversion from G.711 A-law to Prosody 16kbps.

V.29

Fax communication standard, for operation at 9600 bits per second, with fall-back to 7200 bps

V.21

The early standard for communication between modems or Faxes at 300bps

V.23

Standard for modem communication at 1200bps (with 600bps backward channel)

VoIP

Voice over Internet Protocol: Any system which transmits real-time speech (usually duplex) as data over the internet.

VOX

Voice activated recording, or voice activity detection. A file format consisting of raw data, with no length or data format information, used by some speech cards.

WAV

A standard format for storing audio files on a computer. The header on a WAV file describes the format of the data that follows. The data itself can be in virtually any format, as long as the format has a unique name, registered with Microsoft.



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