U.S. patent number 3,855,416 [Application Number 05/311,422] was granted by the patent office on 1974-12-17 for method and apparatus for phonation analysis leading to valid truth/lie decisions by fundamental speech-energy weighted vibratto component assessment.
Invention is credited to Fred H. Fuller.
United States Patent |
3,855,416 |
Fuller |
December 17, 1974 |
METHOD AND APPARATUS FOR PHONATION ANALYSIS LEADING TO VALID
TRUTH/LIE DECISIONS BY FUNDAMENTAL SPEECH-ENERGY WEIGHTED VIBRATTO
COMPONENT ASSESSMENT
Abstract
A method and apparatus for indicating emotional stress in speech
by detecting the presence of vibratto or rapid modulation and
weighting the vibratto with a detected peak value of a preselected
frequency band.
Inventors: |
Fuller; Fred H. (Chevy Chase,
MD) |
Family
ID: |
23206805 |
Appl.
No.: |
05/311,422 |
Filed: |
December 1, 1972 |
Current U.S.
Class: |
704/272;
704/E17.002; 704/270 |
Current CPC
Class: |
G10L
17/26 (20130101) |
Current International
Class: |
G10L
17/00 (20060101); G10l 001/04 () |
Field of
Search: |
;179/1SA,1SB,1US,15.55R,15.55T ;128/2.06 ;35/21 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Lieberman & Michaels, Some Aspects of Fundamental Frequency
& Envelope Amplitude As Related to the Emotional Content of
Speech, J.A.S.A. 7/1962, pgs. 922-927..
|
Primary Examiner: Stewart; David L.
Attorney, Agent or Firm: Fidelman, Wolffe, Leitner &
Hiney
Claims
What is claimed is:
1. A method for detecting emotional stress in the utterance of an
individual comprising:
converting said utterance to an electrical signal;
selecting a frequency band of said electrical signals;
detecting the peak amplitude of said selected frequency band;
simultaneously with said frequency selecting and peak detecting,
smoothing said electrical signals to form an envelope, detecting
rapid aperiodic amplitude modulation on said envelope, and
selecting detected modulation exceeding a preselected
amplitude;
weighting said selected modulating with said detected peak
amplitude; and
displaying said weighted signal which is indicative of emotional
stress.
2. A method as in claim 1 including rectifying and smoothing said
selected frequency band before detecting
3. A method as in claim 1 wherein detecting rapid modulation
includes time and amplitude discriminating said smoothed
signal.
4. A method as in claim 3 wherein said smoothing comprises
integrating and said time and amplitude discriminating includes
differentiating and D.C. base line restoration.
5. A method as in claim 1 including holding said detected peak
amplitude for the duration of said utterance and resetting said
held peak amplitude upon termination of said utterance.
6. A device for indicating emotional stress from the utterances of
a human comprising:
means for converting said utterances into electrical signals;
means connected to said converting means for passing a frequency
band of said electrical signals;
means connected to said band-passing means for detecting the peak
amplitude of said passed electrical signals;
means connected to said converting means for shaping said
electrical signals into an envelope;
means connected to said shaping means for detecting rapid aperiodic
amplitude modulation on said envelope;
means connected to said peak detecting means and said modulation
detecting means for weighting said detected modulation with said
detected peak amplitude; and
means connected to said weighting means for indicating said
weighted signal.
7. A device as in claim 6 including rectifying means and smoothing
means connected between said band-passing means and said peak
detecting means.
8. A device as in claim 7 wherein said band-passing means has a
band of 150 to 300Hz.
9. A device as in claim 7 wherein said peak detecting means also
hold said detected peak until reset.
10. A device as in claim 6 including means connected between said
modulation detecting means and said weighting means for comparing
said detected modulation to a selected level.
11. A device as in claim 10 wherein said modulation detecting means
includes differentiating means producing a series of varying
amplitude pulses and said comparing means producing a series of
uniform amplitude pulses for each varying amplitude pulse above
said selected level.
12. A device as in claim 11 wherein said weighting means produces a
series of pulses whose spacing is that of said comparing means
pulses and whose amplitude is proportional to said detected
peak.
13. A device as in claim 10 wherein said shaping means includes
rectifying means and integrating means.
14. A device as in claim 6 wherein said detecting means include
differentiation means and baseline restoration means.
Description
BACKGROUND OF THE INVENTION
The present invention relates generally to voice signal analysis
systems and more specifically to a method and apparatus for
detecting emotional stress within a voice pattern. The presence of
an emotional state will be used to determine the truthfulness of a
response to questions asked by a skilled interrogator. This
invention must be understood and examined in the light of my
copending applications, Ser. Nos. 311,391 and 311,392. These
inventions provide parts of the technology of this particular
invention which is different from and is an extension of the
technology of both copending applications.
DESCRIPTION OF THE PRIOR ART
It has long been known that the voice may be, and often is, used to
convey the emotions of the speaker. The emotional state of the
speaker produces readily observable variation of measurable
parameters of the voice.
Speech is the acoustic energy response of: (a) the voluntary
motions of the vocal cords and the vocal tract which consists of
the throat, the nose, the mouth, the tongue, the lips and the
pharynx, and (b) the resonances of the various openings and
cavities of the human head. The primary source of speech energy is
excess air under pressure, contained in the lungs. This air
pressure is allowed to flow out of the mouth and nose under
muscular control which produces modulation. This flow is controlled
or modulated by the human speaker in a variety of ways.
The major source of modulation is the vibration of the vocal cords.
This vibration produces the major component of the voiced speech
sounds, such as those required when conus the vowel sounds in a
normal manner. These voiced sounds, formed by the buzzing action of
the vocal cords, contrast to the voiceless sounds such as the
letter s or the letter f produced by the nose, tongue and lips.
This action of voicing is known as "phonation."
The basic buzz or pitch frequency, which establishes phonation, is
different for men and woman. The vocal cords of a typical adult
male vibrate or buzz at a frequency of about 120Hz, whereas for
women this basic rate is approximately an octave higher, near 250
Hz. The basic pitch pulses of phonation contain many harmonics and
overtones of the fundamental rate in both men women.
The vocal cords are capable of a variety of shapes and motions.
During the process of simple breathing, they are involuntarily held
open and during phonation, they are brought together. As air is
expelled from the lungs, at the onset of phonation, the vocal cords
vibrate back and forth, alternately closing and opening. Current
physiological authorities hold that the muscular tension and the
effective mass of the cords is varied by learned muscular action.
These changes strongly influence the oscillating or vibrating
system.
Certain physiologists consider that phonation is established by or
governed by two different structures in the pharynx, i.e., the
vocal cord muscles and a mucous membrane called the cones
elasticus. These two structures are acoustically coupled together
at a mutual edge within the pharynx, and cooperate to produce two
different modes of vibration.
In one mode, which seems to be an emotionally stable or
non-stressful timbre of voice, the conus elasticus and the vocal
cord muscle vibrate as a unit in synchronism. Phonation in this
mode sounds "soft" or "mellow" and few overtones are present.
In the second mode, a pitch cycle begins with a subglottal closure
of the conus elasticus. This membrane is forced upward toward the
coupled edge of the vocal cord muscle in a wave-like fashion, by
air pressure being expelled from the lungs. When the closure
reaches the coupled edge, a small puff of air "explosively" occurs,
giving rise to the "open" phase of vocal cord motion. After the
"explosive" puff of air has been released, the subglottal closure
is pulled shut by a suction which results from the aspiration of
air through the glottis. Shortly after this, the vocal cord muscles
also close. Thus in this mode, the two masses tend to vibrate in
opposite phase. The result is a relatively long closed time,
alternated with short sharp air pulses which may produce numerous
overtones and harmonics.
The balance of respiratory tract and the nasal and cranial cavities
give rise to a variety of resonances, known as "formants" in the
physiology of speech. The lowest frequency format can be
approximately identified with the pharyngeal cavity, resonating as
a closed pipe. The second formant arises in the mouth cavity. The
third formant is often considered related to the second resonance
of the pharyngeal cavity. The modes of the higher order formants
are too complex to be very simply identified. The frequency of the
various formants vary greatly with the production of the various
voiced sounds.
As pointed out in my copending applications, the fine structure of
the fundamental pitch frequency, as well as the relative peak
energy at high and low frequency regions, appears to be an acoustic
correlate of emotional content, transmitted through speech. Other
parameters thought to be related to the emotional transmission of
information include: Phonetic Content, Gross Changes in Fundamental
Frequency, Relative Energy Levels in Various Frequency Bands, and
the Speech Envelope Amplitude. These parameters all contribute to
the conveyance of emotion or a stressful condition existing in the
speaker.
Speech analysis and the equipment for accomplishing the same has
been developed for a variety of loosely related purposes. One of
the primary concerns is the transmission of speech with a high
order to intelligibility and presence over a very reduced
bandwidth. The applicability of this particular art becomes obivous
in civil and military communications. Other fields in which speech
analysis equipment are used are the voice operated printing or
recording device, such as a typewriter and systems, equipment and
devices commanded and controlled by the spoken word or phrase.
While these activites are interesting and valuable in themselves,
they do not relate to the detection of emotional content of a
speech wave nor to its use to determine the veracity of the
speaker.
According to the present invention, the fine structure of the basic
phonation may be assessed and quantified by measurement of the
amount of rapid amplitude modulation on the speech signal envelope
of a spoken word and weighted by the peak amplitude in a selected
frequency band. This rapid variation of the speech signal is called
"Vibratto" for the purposes of this application.
This invention discloses a means whereby the measure of vibratto in
the speech envelope of a person under interrogation may be
meaningfully quantified in real time, so that a Truth/Lie decision
can be made. Research into the vibratto component of the speech
wave has conclusively demonstrated that the amount of vibratto
correlates well with stress or emotional involvement which leads to
the Truth/Lie decision.
There are many ways to detect and measure the amount of vibratto in
the phonation of an emotionally involved person under
interrogation. Frequency fluctuation in the basic pitch frequency
could be quantified with the aid of a frequency discriminator, for
example. In addition, variations in the time between successive
pitch pulses could be obtained by conventional zero crossing
analysis.
SUMMARY OF THE INVENTION
The present invention provides a means for determining the truth
and veracity of a speaker's response under interrogation by
quantification of vibratto content of his answer and weighting such
quantification with the peak amplitude in a selected frequency band
of his speech. The vibratto is quantified by rectification,
smoothing, time and amplitude discrimination and level detected to
produce a series of pulses of uniform width and amplitude. These
pulses represent the vibratto content. Simultaneously in a parallel
circuit, the speaker's voice peak is detected by processing the
signal through a band pass filter, rectifier, smoothing filter, and
peak-detection-and-hold circuit. The vibratto pulse train is
weighted by multiplying it by the detected peak amplitude in an
analog manner. The resulting pulse train is a series of pulses
whose timing is related to the vibratto content of the speech and
whose amplitude is proportional to the peak energy level in the
fundamental pitch region as selected or defined by the band pass
filter in the peak detector circuit.
Though using an analog multiplier to weight the two functions is
simple and straightforward, other means are available for producing
the desired weighted function. For example, the two signals may be
recorded in a two-track chart recorder and the value of the
vibratto pulse could be multiplied by the peak voltage reading by
hand. The vibratto measurement could also be quantified by digital
counter with the resultant number being multiplied by the voltage
reading of the peak energy circuit. Similarly, instead of using a
DC chart recorder, the output from the analog multiplier may be
further quantified by measuring the average value with a simple DC
voltimeter or with an averaging and recording instrument.
The present invention provides a visual real-time display of a
weighted vibratto content of the speech of the subject from which a
trained interrogator may derive the veracity thereof by comparison
with a known truthful response.
OBJECTS OF THE INVENTION
It is an object of the present invention to provide a means for
detecting a stressful or emotional condition in a human being who
is speaking.
An additional object of this invention is to detect this emotional
or stressful condition while the person who is speaking is under
direct and skillful interrogation.
A further object of this invention is to provide means whereby a
valid Truth/Lie decision can be rendered by direct observations of
the data readout of a voice or speech analysis system.
A still further object of this invention is to detect the emotional
or stressful condition by analysis of the vibratto content of
speech weighted by the peak amplitude of a selected frequency band
during the same phonation utterance.
Other objects, advantages and novel features of the present
invention will become apparent from the following detailed
description of the invention which considered in conjunction with
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an oscillograph of a male voice responding with the word
"yes" in the English language, in answer to a direct question at a
bandwidth of 5kHz,
FIG. 2 is an oscillograph of a male voice responding with the word
"no" in the English language in answer to a direct question at a
bandwidth of 5kHz,
FIGS. 3a and 3b are oscillgraphs of a male voice responding "yes"
in the English Language as measured in the 150-300Hz and 600-1200Hz
frequency regions, respectively,
FIGS. 4a and 4b are oscillographs of a male voice responding "no"
in the English language as measured in the 150-300Hz and 600-1200Hz
frequency regions, respectively,
FIGS. 5a and 5b are graphs of a "yes" response with and without
emotional stress, respectively.
FIGS. 6a and 6b are graphs of a "no" response with and without
emotional stress, respectively.
FIG. 7 is a block diagram of the weighted vibratto signal
processing circuit,
FIG. 8 is a detailed schematic of the weighted vibratto signal
processing circuit.
DESCRIPTION OF PREFERRED EMBODIMENTS
FIG. 1 shows an oscillograph of a male voice responding with the
word "yes" in the English language in answer to a direct question
at a bandwidth of 5kHz. The wave form contains two distinct
sections, the first being for the "ye" sound and the second being
for the unvoiced "s" sound. Since the first section of the "yes"
signal wave form is a voiced sound being produced primarily by the
vocal cords and conus elasticus, this portion will be processed to
detect emotional stress content or vibratto modulation. The male
voice responding with the word "no" in the English language at a
bandwidth of 5kHz is shown in FIG. 2. This response has a single
voiced section which will be analyzed by the present device to
detect the presence of the vibratto or rapid modulation of the
phonation constituent of the speech signal.
FIGS. 3 and 4 show an oscillograph of the same male voice as in
FIGS. 1 and 2 responding "yes" and "no," respectively, in the
English language as measured in the 150-300Hz frequency region.
This spectral region contains a great deal of the fundamental
energy of phonation. When this band of frequencies is rectified and
smoothed, the peak amplitude of the phonation will make an ideal
weighting function.
FIG. 5a is a drawn replica of a portion of the response "yes,"
delivered under emotional stress. The rapid modulation or vibratto
pulses can be seen extending above and below the normal envelope.
These additional excursions occur as the result of non-symmetric
action between the vocal cords and the conus elasticus. The basic
repetition period of this male voice is about 8.3 milliseconds.
FIG. 5b is a drawn replica of a portion of a male voice responding
"yes" delivered under conditions of no emotional stress. The smooth
regular features of the pitch pulses can be easily seen.
FIG. 6a is a drawn replica of a portion of the same male voice
responding "no" under a condition of emotional stress. The vibratto
modulations appear as distortions near the axis of averages and as
excessively high peaks in the position direction. This
non-regularity is the result of interaction in the pharynx between
the vocal cords and the conus elasticus leading to an "explosive"
type of formant excitation.
FIG. 6b is a drawn replica of a portion of the same male voice
answering "no" to a non-stress question. The smoothness and
regularity of the response can be readily seen.
Thus it is an object of the present invention to isolate the rapid
modulation of the phonation constituent of the speech signal
envelope in order to detect the presence of emotional stress in the
speaker.
The components for achieving the stated objectives are shown in
block diagram form in FIG. 7. As in the previous copendng
applications, a high fidelity acoustic transducer 2 is used to
bring the transduced electrical energy of the phonation into the
system. The electrical signal divides into two channels. The upper
channel is concerned with the speech processing of the Fundamental
Pitch Frequency, and the lower channel processes the Vibratto
Component of the voice.
In the upper channel, an amplifier 4 serves to increase the energy
of the signal from the transducer and to isolate the following
circuits from the output impedance of the transducer. A band-pass
filter 6 follows, which is selected or adjusted to accept only the
fundamental pitch frequency of the voice. This is commonly found to
be in the vicinity of 120 to 150Hz for men and about 250Hz for
women and thus a filter with a bandwidth of 150-300Hz may be
selected. The signal at the output of band-pass filter 6 is tied to
the energy detection means which comprises a rectifier 8 followed
by a smoothing or low pass filter 10. By this pair of circuits, a
voltage which is representative of the envelope of the phonation is
produced. This envelope is then peak detected and held or stored in
device 12 until all further processing has been accomplished. The
circuit is then reset, either manually or automatically, as desired
by the operator of the machine.
In the lower channel, the electrical signal from the transducer 2
is amplified and isolated by amplifier 14. The energy is again
rectified by rectifier 16, isolated and amplified by amplifier 17
and smoothed by filter 18 to form an envelope of the signal. At
this point the bandwidth of the signal in the lower channel is
unrestricted. The smoothing filter 18 must have its characteristics
adjusted accordingly. Following this filter, a stage of isolation
amplification 20 is used to separate the processing of the
smoothing filter from the time and amplitude discriminator 22. This
latter circuit acts to compare the amplitude of the signal envelope
with the time derivative of the signal envelope.
The output of the time and amplitude discriminator 22 is a zero
based burst of pulses of a single polarity. These pulses will have
a high proportion of the vibratto component. The pulses, which are
of varying amplitude and width, are fed into a voltage comparator
24, a module of conventional design and commercially available. The
comparator compares the incoming wavetrain with a DC voltage from
the potentiometer 26. The only pulses that are allowed to emerge
from the comparator are those that are larger in voltage value than
the set voltage of the potentiometer. This potentiometer is set by
the operator to a value which is somewhat above the baseline. It
has been demonstrated experimentally that the Vibratto Component is
usually of high sharp pulses, so these are enhanced with a high
setting of the potentiometer. The output of the comparator is a
series of pulses, predominantly consisting of the Vibratto
Component, all of constant amplitude one for each pulse exceeding
the preset level.
The detected and held envelope peak enters input port 27 of the
analog multiplier 28, while the series of vibratto pulses enters
input port 29. These two waveforms are multiplied together in the
mathematical manner known as "weighting." The result will be a
series of pulses of increased amplitude at a period defined by the
vibratto pulse train at input port 29 that will be recorded in the
DC recorder 30 for observation and analysis.
A more detailed explanation of the preferred embodiment of the
invention is shown schematically in FIG. 8.
The acoustic phonation of the subject under interrogation enters
the system of instrumentation in one of two ways. It may, at the
discretion of the operator, enter the system directly (in real
time) from the transducer 50 or from tape recorder 54 and its
transducer 52. These transducers are high fidelity microphone types
of devices that reproduce the electrical analog of the acoustic
signal, with a minimum of frequency and amplitude distortion.
Switch means 56 is used to select either the microphone directly or
the tape recorder output. As in FIG. 7, the upper channel in FIG.
8, pertains to the envelope processing and peak detection of a
selected frequency band and the lower channel pertains to the
envelope processing and vibratto quantification.
The switch means 56 is followed in the upper channel by an
operational amplfier 58 with its gain determining resistors 60 and
62. The broad band speech signal from the transducer and switch
enters the band pass filter 64 and the spectral region typically
from 150-300Hz is allowed to pass. This exact region may be
changed, depending upon the voice of the subject involved. The
region of 150-300Hz is a good compromise and was employed in the
preferred embodiment. FIGS. 1 and 2 show the waveforms of a male
human voice responding the words "yes" and "no" in English when the
bandwidth is limitd to 150-300Hz.
Another stage of isolation, employing an operational amplifier 66,
with its gain determining resistors 68 and 70, is used to isolate
the band-pass filter from the converter of the dual polarity
signals. In the preferred embodiment of the invention, the
conversion of the dual polarity signals out of the isolation
amplifier are performed by a simple solid state diode 72 acting as
a rectifier. A reversed polarity diode would function nearly as
well. In addition, full wave or bridge rectifiers could also be
used with attendant increase in signal level. If diodes with a
particular characteristic, such as "Square Law" were employed, the
instrument would operate upon a true measure of the "power" in the
speech signal. A further operational amplifier 74 with its gain
setting resistors 76 and 78 serves to isolate the rectifier circuit
from the rest of the instrument. A smoothing filter 79 follows this
amplifier.
The smoothing filter consists of a low-pass filter network that is
comprised of a variable resistor 80 and a fixed capacitor 82. It
can be seen that other types of low-pass filters could be employed
here, to remove the higher frequency fluctuations of the rectified
signal, thus rendering the output of the smoothing filter
essentially that of the envelope of the speech wave, in the defined
pass-band. The exact time constant of this filter is adjusted
depending upon the pitch of the voice under assessment. The
smoothed envelope is amplified and isolated by operational
amplifier 84 with its gain determining resistors 86 and 88. This
envelope of speech energy then passes into a peak detect and hold
circuit 90 of conventional design. Such circuits can be readily
fabricated from a variety of components and modules by those
skilled in the art. It is preferred to use a single circuit to
perform this task such as a single module named "Infinite Sample
Hold," manufactured by Hybrid Systems Corp. This particular module
has the advantage of preventing decay of the peak value until the
circuit is reset by a signal on input lead 94 from the control
means 96 which may be a simple switch. The output peak value
appears on lead 92 and is applied to one channel of the analog
multiplier 98. There are many ways that two voltages could be
multiplied together, thereby "weighting" or modulating one voltage
with the other. This process could be performed manually, by
obtaining the individual values of the voltages involved. It is
preferred, however, to employ one of the modern analog computer
modules that have become available such as Model 107C analog
multiplier/divider, manufactured by Hybrid Systems Corp.
The lower channel that processes the speech or phonation energy to
obtain the Vibratto components functions in the following manner.
The electrical analog of the phonation enters the channel through
an isolating operational amplifier 103 with its gain determining
resistors 104 and 106. This amplifier is used to provide isolation
and linear amplification of the signal with no frequency
discrimination. This isolated and amplified signal is applied to a
diode 108 where one polarity of the speech signal is allowed to
pass into the following circuitry. A diode connected in the
opposite polarity could be used nearly as well. A full wave
rectification circuit or a bridge rectification circuit (not shown)
could be used as well with a small additional complication of the
circuit.
The electrical energy out of the diode, at the input of the
following circuitry, is therefore predominantly and primarily of
one polarity. Operational amplifer 110, with its gain determining
resistances 112 and 114 is used to isolate the diode circuit from
the follow-on circuitry. The follow-on circuitry consists of a
smoothing filter 116 in the form of an R/C Integrator having a
variable resistor 117 and a fixed capacitor 118. It can be seen, by
those versed in the art, that a variety of different active and
passive smoothing filters could be used to remove the high
frequency energy of the phonation and to extract a signal which is
representative of the envelope of the speech wave and yet retains
the Vibratto Component. The R/C Integrator that is used in the
present preferred embodiment functions quite well and is simple to
employ. The time constant is variable to afford adjustment for
different voices of various fundamental frequencies.
The R/C Integrator is folowed by another operational amplifier 120
with its gain determining resistors 122 and 124. This operational
amplifier isolates the processing of the R/C Integrator from the
subsequent circuit action. Following the isolation amplifier 120 is
a special discriminator circuit that processes the time derivative
of the incoming speech wave and the amplitude of the speech
envelope at the same time. The special differentiator circuit
involves a fixed capacitor 126 and a variable resistor 128. These
two components perform the time differentiation function. The
potentiometer 130 provides a measure of the undifferentiated signal
envelope which is used to null out residual envelope energy. This
component, connected as it is, performs the envelope amplitude
discrimination function. An operational amplifier 132, with its
gain and performance determining resistances 134, 136 and 138,
accepts the time derivative signal and the amplitude discrimination
signal and provides effective base line restoration for most types
of phonation.
Base line restoration can be accomplished in a variety of ways as
well, as by various types of clamping and DC restoration circuits.
Irrespective of the circuit of use, the output of the amplifier 132
becomes a series of pulses with a defined base line that contains
the Vibratto Component and thus comprises the variable fine
structure of the phonation. These pulses are of varying amplitude
and width.
The output pulses from the time and amplitude discriminator are
applied to a comparator circuit 140 which determines the level of
statistically signifcant pulses. This level is determined by a
knowledgeable operator of the equipment, and is controlled by
adjustment of potentiometer 142. This control is shown to function
at either a positive or a negative voltage level. When the polarity
of the diode 108 is selected, the comparator voltage level must be
adjacent to the polarity that will select either excess positive or
excess negative peaks. The potentiometer 142 may also be set at "0"
volts at which time the circuit becomes conventional zero-crossing
detector means. It has been found that the statistical significance
of the Truth/Lie Decision process will improve if a level of
voltage off the "O" baseline is selected for the comparator
switching level. This comparator may be a simple diode circuit or
it may be a Schmitt trigger circuit, each with suitable voltage
supplies, passive and active components. However, for simplicity
and economy, a differential voltage comparator such as the Motorola
MC1710 was used. The output of voltage comparator 140 is a series
of equiamplitude pulses, one for each input above the selected
level. This pulse train enters the analog multiplier 98, where it
is "weighed" by the output voltage level of the peak detect and
hold module 90. The output pulse train thus has an amplitude varied
by the peak detected signal and a spacing of the vibratto pulse
train.
The algebraic analog product of these two voltages emerges from the
multiplier module on lead 100 and enters a DC chart recorder 146.
The responses of each utterance of phonation from the subject under
interrogation are thereby recorded for comparison and analysis. The
chart recorder is also under the control (on cable 148) of the
control means 96. By this means, prior to the act of asking a
particular question, the operator/interrogator erases or resets the
sample and hold voltage level from module 90 and primes the chart
recorder. Immediately after the question is asked, the circuits are
all enabled by the control means so that the phonation of the
subject may be processed by the instrumentation. Although the
invention has been described and illustrated in detail, it is to be
clearly understood that the same is by way of illustration and
example only and it not to be taken by way of limitation, the
spirit and scope of the invention being limited only by the terms
of the appended claims.
* * * * *