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Technology providers usually offer speaker verification sytems that could be integrated
in products. In this section, we examine a few examples.
- VOCALIS Ltd. (at that time part of LOGICA) developed a real-time
telephone-based
text-dependent system in 1988. The system's decision making logic has four layers of authentication
prior to making the final decision on the claimed identity of the speaker. Individual password
and PIN are used as the first two layers of authentication. A number of words from pre-defined
vocabularies are also chosen randomly at the later stages of verification. The enrolment process follows
a robust strategy, in order to guarantee that the reference template is relevant. VOCALIS' speaker
verification system is developed for a UNIX platform and makes use of embedded hardware.
It is fully integrated into the company's communications infrastructure.
An extensive field trial of the system was organised in conjunction with a telephone service company
in the US, where over 400 people from four different geographical groups registered with the system.
The system allowed users to access US Government databases out of office hours. All registered
participants were encouraged to make at least ten calls over a three month period, using as many handsets
as possible. The registered speakers were also asked to make two impostor
calls and were purposely provided with information to break the first two layers of authentication.
At the end of the trial, more than 4000 calls were logged. A detailed analysis of the results showed
a 5% equal error rate purely for the verification algorithm. None of
the participants managed to break into the system as impostors when all layers of authentication were
active. A similar speaker verification system is available also on the Callserver platform
from VOCALIS.
- ENSIGMA Ltd. proposes a speaker verification system named VERIFIER
[Moody (1991)], which runs on the Loughborough AT&T DSP32C telephone
board. It works both over telephone line and audio line. ENSIGMA
claims full portability of the speaker verification software on other
boards. The system uses a new approach to the speaker verification
problem. In fact, instead of simply matching a speaker's voice against
the user's template, ENSIGMA's system compares the spoken word also
against a ``general world model''. The decision is made taking into
account the results of these two comparisons. This method has been
evaluated over the telephone line and gives 1% false rejections
and 1% false acceptances . The method also seems
quite robust to
background noise . Enrolment consists of the new user repeating a
series of digits; the duration of this phase is about one minute. The
access consists of the pronunciation by the user of a list of (random)
digits requested by the system. System response takes about 5 seconds. The
VERIFIER has many properties that make this system a good candidate as
a possible reference hardware system for (text-dependent) speaker
verification . The multilingual aspect, or generally speaking the
vocabulary problem, may be solved only if procedures to build the
``reference world model'' used to score utterance similarity is
released by the producer.
- The CNAPS of Adaptive Solution Inc. works over the telephone line and
gives both speaker verification and speaker identification
capabilities [Skinner et al. (1992)]; averaging the true acceptance and true
rejection rates the system reaches 95% of correct
responses for speaker identification and 97% for speaker verification . These
results refer to a field test where the user pronounces the seven
digits of their PIN to access a system; for speaker verification, the user
communicates a reference number using DTMF to the receiver
before starting to pronounce the seven digits.
Voice Control System offers speaker verification
in their speech
recognition system over the telephone line. It works on several platforms
including PC and
VME . By August 1990 [Hunt (1991)] the performance was
1% false acceptances and 2% false rejections.
A speaker verification facility is also part of the AT&T HuMaNet
teleconferencing system [Berkley & Flanagan (1990)] that works via ISDN and uses
an AT&T digital signal processor DSP32C board on a
Personal Computer .
The main problem which service providers and integrators have to face is to be able to predict what level of performance and user satisfaction they are going to get from a given technological solution.
Next: Examples of speaker verification
Up: Applicationssystems and products
Previous: Typology of applications
EAGLES SWLG SoftEdition, May 1997. Get the book...