The application of speech recognition technology in the Army command and control area is presented. The problems associated with this program are described as well as as its relevance in terms of the man/machine interactions, voice inflexions, and the amount of training needed to interact with and utilize the automated system

Hadden, David R.

Haratz, David

English

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T"N 9 3 - 7 2 6 2 8
THE ARMY WORD RECOGNITION SYSTEM
DAVID R. HADDEN
DAVID HARATZ / *7 £>3
U.S. ARMY COMMUNICATIONS RESEARCH &
DEVELOPMENT COMMAND (PROVISIONAL)
FORT MONMOUTH, NEW JERSEY
REPRODUCIBILITY OF 'ii,_
1. INTRODUCTION ORIGINAL PAGE IS POOR
In many cases, the spoken word still represents man's most
effective and efficient means of communication. Either in the input or
output mode, the spoken word can represent an important methodology for
man/machine interactive communications in future army tactical communica-
tions, command and control (C ) systems as we move into future weapons
and control systems heavily dominated by digital computer technologies.
The major areas of applicability for word recognition systems within the
field army encompass aspects relevant to overall system man/machine reli-
ability as compared to other interactive senses, i.e., touch, sight, etc.
Although previous efforts have been primarily aimed at providing two-
way verbal communications between front-line personnel (i.e., artillery
forward observer) and an army tactical data system, near-term future
directions will attempt to primarily tackle a subset of this very complex
problem in terms of shelter oriented terminals encompassing console oper-
ations applicable to a wide range of source data automation (SDA) prob-
lems.
The Army's initial effort in the application of speech technol-
ogy to Army tactical data systems was called Word Recognition System (WRS)
The WRS was addressing the problem of the frontline troops (artillery
forward observer) who must get information to a computer based system
(i.e., TACFIRE). The primary thrust in this area was the keyboard entry/
display device called the Digital Message Device (DMD). The alternative
of the WRS was very appealing as it meant that the forward observer need
only carry the radio as 'in a non-automated system and the required pro-
cessing could be colocated with the action computer. The requirement
for the WRS was therefore a limited vocabulary in a structured message
format but with a variety of individual voices and Army tactical communi-
cations .
II. PRESENT STATUS FEEDING, PAGE BLANK NOT FILMED
An advanced development model of a Word Recognition System (WRS)
was developed fdr the Army aimed at providing two-way verbal communications
PRECEDING PAGE BLAMK f40T FILMED
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between front-line personnel and Army Tactical Data Systems (ARTADS)
using discrete word recognition, speaker identification/verification and
voice response techniques. The minicomputer based WBS is capable of
fully automated real-time prompting, message translation and synthesized-
speech response over a communication net for any of 64 users with a
vocabulary of approximately 150 words. The vocabulary and syntax are a
subset of messages that are capable of simulating forward observer inputs
to TACFIRE via a Digital Message Device (DMD).
The WRS recognizer is an acoustic pattern classifier that
produces a digital code as an output in response to the received utter-
ance.. It consists of a spectrum analyzer, an analog multiplexer and A/D
converter (ADC), a programmed digital processor, a reference-pattern
memory, and an output register as shown in Figure 1. The spectrum analyzer
divides the input audio spectrum into 16 frequency bands that cover the
useful frequency range. By means of parallel detection and lowpass filter-
ing the resulting 16 analog signals represent a power spectrum that consti-
tutes the feature for speech classification. These 16 continuous signals
are multiplexed, sampled at 100 Hz, and converted to digital form with
8-bit precision. Thus, the original utterance arrives at the digital
processor as a string of 8-bit binary numbers. The coding compressor
compensates for changes in the rate of articulation and reduces the spec-
tral data generated by each utterance to a fixed-length code for the
classifier. It reduces every word, .regardless of length, to a 240-bit
pattern; for a word lasting two seconds the data compression exceeds
100 to 1. As a result, the fixed-length codes can be processed in real
time by pattern-recognition techniques. The compression algorithm is
essentially an arithmetic process which preserves selected property
changes during an utterance and eliminates periods during which these
properties remain constant.
The word boundary detector serves to establish the start and
end of each utterance for the compressor by means of experimentally
determined criteria. During the training or adaptation phase of system
operation, approximately five utterances of each vocabulary word are
elicited from the user. The estimator compensates for variations among
these utterances to form a single, 120-bit reference pattern, and a 120-
bit mask that is stored in memory to represent a particular vocabulary
word. These 240 bits represent both the tendencies that are common to
the five utterances and the small variations that are inevitable from
utterance to utterance.
After the system has been trained to a particular user, each
new 120-bit pattern from the coding compressor is compared with a syn-
tactically determined subset of all the previously learned reference
patterns in memory. Basically the classification process matches the
patterns bit by bit via an exclusive-OR function that produces an output
for each matching pair of bits. The total number of outputs is counted
for each of the reference patterns; the one pattern that produces the
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greatest number of outputs above a preset reject threshold classifies the
compressor output and thereby the received utterance. The voice-response
technology in WRS is an off-the-shelf Votrax module from the Vocal Inter-
face Division of Federal Screw Works, Troy, Michigan. It is an audio
synthesizer programmed to produce strings of phonemes and phoneme-like
 :
sounds with inflection to produce words.
Training or adaptation of the system to each of the 64 users
may take place at the WRS site or via the communications link. The entire
recognition vocabulary of about 150 words must be trained by each user
by means of approximately five repetitions of each word. This vocabulary
is divided into groups of about 30 words each to ease the training regimen.
A single word retrain capability also exists. The user is prompted
throughout the training regimen by voice response from the system.
A.. Hardware Design.
In the area of hardware design, the driving factor was the
requirement for a field-deployable, ruggedized system to demonstrate the
overall feasibility of word recognition in a semi-tactical environment.
This necessitated the selection of an existing ruggedized processor and
memory, the Rolm 1602. The hardware consists of the 1602 processor and
memory, a number of standard peripherals, and the WRS preprocessor that
was designed and fabricated by the contractor, SCOPE Electronics Inc.,
Reston, Virginia.
The CPU and its piggyback memory chassis occupy one drawer.
An external memory chassis occupies another. Main memory is 32K 16-bit
words of core, which is expandable to 64K as required through the addition
of another piggyback memory chassis behind the Rolm 2143. The moving-
head disk controller and disk drive are driven from the processor chassis;
the disk is utilized to store user reference patterns and the operational
software. A third Rolm Chassis provides access to the I/O bus for most
of the peripherals. The CRT terminal serves as the operator display and
control device. The line printer is the principal output device used to
simulate messages transmitted to ARTADS. The magnetic tape unit is a
backup storage and loading device for user reference patterns and
operational software. The card reader, the paper tape reader, and the
backup ASR33 terminal are used solely for software development.
All non-digital interfaces are made to the WRS preprocessor,
which occupies one drawer and includes all of the front-end hardware for
speech recognition and the computer interface speech synthesis. The
hardware configuration of the WRS preprocessor and associated Votrax
modules is shown in Figure 2. Each of the three net inputs (only one is
implemented) may interface with: 1) a field telephone, 2) either of two
types of non-secure FM radio transceivers, or 3} either of two types of
secured FM radio transceivers. The net control module provides the neces-
sary R/T switching functions and permits the operator to monitor any one,
none, or all three nets at this option. A connection is brought to the
210
Figvire 2. WRS Preprocessor Module and Votrax
211
front panel for the operator headset and a demonstration speaker that
reproduces sound in the operator headset. A foot switch is provided for
the operator's push-to-talk function. A voice response unit interface
module was developed for communication between the I/O bus and the three
voice response units (one per net).
Input speech signals arrive at the audio modules from either the
communications nets or test microphones. Each audio module amplifies
and modifies the incoming frequency spectrum to compensate for communications
degradation and user microphone characteristics. Each of the three filter/
ADC modules then performs the spectral analysis, MUX, and ADC functions
as previously described. A single ADC interface module controls the
sampling, channel selection, and A/D conversion processes by software
command.
Two modular power supplies provide the requlated DC power
required by the preprocessor. A frequency-selectable source for the real-
time clock permits experimental variation of the speech sampling interval.
Preprocessor front panel indicators include (for each net) a meter, a
word.-boundary indicator that illuminates during each word, and an
overload indicator to reveal saturation of the A/D converter.
B. Software Design
In the area of software design and implementation, the two
primary requirments imposed encompassed the necessity for user indepen-
dence and for system flexibility. The term "user independence" means that
the performance of the system, as seen by one user, is unaffected by the
status of the other system users. In this definition, the operator is
considered as the fourth user of the system, since he is in competition
with the three potential "verbal" users for the system facilities and must
also be serviced in a manner which does not degrade with increased usage
of the speech channels.
Because the purpose of WRS was to provide a system which
was to be used to determine the suitability of this approach to field use,
a high premium was placed on overall system flexibility. This requirement
was addressed by a design philosophy which required that all application-
dependent parameters be input from the outside—via a system configuration
tape—rather than from the inside (that is, imbedded in the program it-
self) . Thus, although the system was configured to operate within the
constraints of the TACFIRE (and TOS^) syntax structures, it may easily be
adapted to changes in these specifications or to entirely new vocabulary
and syntax structures.
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The executive system provides for both user independence
and system flexibility through a structure based on the use of a separate
user-state array for each user. This array contains all the variables
needed by the system to completely describe the operating state of the user
and also includes locations which may be used by each user to store
application-dependent data during speech processing. Because all perti-
nent variables are located in a continguous array, the addition of some
simple commands allows the system to manipulate the user-state array and,
therefore, the user's actual status in a very flexible manner.
This flexibility may be enhanced even more if the commands
which are used to manipulate the user-state array can be input as data
and triggered through a variety of inputs. Because different applications
of the executive system will involve potentially different vocabulary
sizes, syntax structures, and even numbers of users, it is important that
the allocation of memory be as flexible as possible. The executive
accomplishes this goal through use of a set of memory management routines
that allocate memory on an as-needed basis. Thus, any required memory
tradeoffs may be made during system configuration.
In addition to providing the facilities described above,
the executive system also supports two file structures that are used to
describe the syntax and vocabulary for a particular application. One
file type—string files—is used to allow the specification of variable-
length byte strings for output to various devices. Since each byte may
be either an ASCII character or a binary phoneme code, this file is used
to store both ASCII data for eventual output to standard devices (such as
the console CRT and printer) and data for output to the voice response ,
units.
The second file type—link files—is used to build three-
structure files that represent the desired syntax structure and, in a
separate file, the command strings associated with various action trig-
gers. Both these link files are constructed during the input of the sys-
tem configuration tape. This is in keeping with the overall design goal
of allowing application-dependent data to be input from the outside
instead of tied directly to the program.
In order to fulfill the requirements of the Word Recogni-
tion System several additions were, needed to the facilities provided by
the aforementioned executive. Perhaps the most far-reaching addition was
the inclusion of a 500K word capacity moving-head disk system. Because
of the disk, the executive has been modified to operate under the vendor-
supplied disk operating system-RDOS. This addition relieved much of the
burden of I/O device management and task scheduling from the executive
system.
In addition to the disk software, two additional tasks have
been added that run in parallel with the system and share certain seg-
ments of data. The first of these is the display routine, which is
213
responsible for updating the CRT to represent the current status of each
system user. The screen is divided into thirds, with each segment repre-
senting one of the three nets. The exact format of the display for each
channel depends on the status of the channel at that time, but during
normal operation the message entered by the remote user will be reflected
on the CRT as it is spoken. The second extra task is operator control.
This allows the operator to modify the status of any user and, if neces-
sary, make corrections in the recognized data.
Although these two tasks are independent in time relative
to the operation of the executive system, it is obvious that a good deal
of information sharing between these processes is required. Once again,
this function is provided by the user-state arrays. For example, during
recognition the message status is maintained in the appropriate user-
state array. Thus, the display routine needs only to access this informa-
tion to display the proper data, and the operator control task also has
access to the same data in order to modify the message.
C. Results of WRS
The requirement for translation accuracy of WRS is 95% over
a field radio link with an S/N ratio of 10 dB. This was not acheived.
The present design proved unsatisfactory over typical Army radio links.
Over an optimal radio link using the international phonetic alphabet,
accuracies up to 97% have been observed. Design of the recognition algo-
rithm attempts to minimize WRS sensitivity to amplitude and time variations
in the utterance of any word, but tends to be sensitive to normal varia-
tions in the speaker's voice, microphone position and background interfer-
ence.
The critical problem areas appear to be the degree of user
training requirements and its impact on overall system reliability. In
complex and highly critical waspons and control systems environment for
example, an average 95% reliability figure just will not do the job.
Neither will complex system user training procedures suffice in terms of
multi-user requirement on a potential quick-response requirement. The
present Army Word Recognition System requires the user to repeat each vocab-
ulary word approximately five times to develop reference patterns, and
complete reference patterns must be stored for each user. With resultant
message translation in the 90-95% range in a laboratory environment, the
need for additional development effort is readily apparent.
III. SUMMARY AND FUTURE DIRECTION
The application of the speech recognition technology to the Army
command/control area presents unique problems as demonstrated by the WRS
system. The conflicting requirements for minimum training of the WRS and
either a small vocabulary with a broad variation in voice types or a large
vocabulary with a limited set of voices present significant complexities
214
to the recognition algorithms. The quality of the Army tactical communi-
cations has had a severe impact on the WRS and will force a significant
rethinking of the basic approach. The voice communications channel quality
is a fact of life that must be overcome if remote voice to computer input
is to become a practical reality.
The use of the WRS capability in the console command/control
arena eliminates the communications channel problem, but to be useful
discrete WRS must provide a much more flexible interaction with a larger
vocabulary. The problems of background noise and voice variations remain
for this applications area too.
The application of speech recognition technology to tactical
military problems introduces a new variable which is unique: stress.
What changes take place in the voice input due to stress and how do these
effect the recognition process? We could be put in the unacceptable
position of having the voice input capability fail us when we need it most.
The capability of speech input and output would be a very valu-
able one in terms of the man/machine interaction for Army command and con-
trol applications. The amount of training the soldier would require in
order to interact with and utilize the automated system would be decreased.
The man/machine interface would be more "natural" and smoother when it
includes keyboard and voice inputs and display and voice outputs. As we
have seen from WRS, this is a difficult problem which requires more devel-
opment effort. The Army is interested in the support of such effort.
ACKNOWLEDGMENTS
The material used for this presentation was taken primarily from
the Draft Final Report of the Army Advanced Development Model Word Recog-
nition System (WRS). The WRS program was funded by PM, Army Tactical Data
Systems (ARTADS) under the technical direction of Michael Simpson, John
Preusse and Merle Hooten. Project personnel at SCOPE Electronics Inc.,
Reston, Virginia included Joseph C. Brown and Shiraz G. Bhanji.
BIOGRAPHICAL SKETCH
David R. Hadden, Jr.
Education: Reed College, Portland, Oregon, BA (Physics), 1959
University of Pennsylvania, MSB (Computer Science), 1971
1960 to Present: Communications/ADP Laboratory, US Army Electronics
Command. Worked in various areas of computer research
and development; data storage techniques and technology
and computer system design and interface standards.
Most recent work has been in the areas of computer
terminals and micro-processor applications.
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The Army word recognition system

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