Technology to improve speech in the hearing disabled
by Patrick Coyne
 Severely
deaf children cannot hear their own voices. Therefore they cannot monitor and
control their voice pitch as hearing people do. Teachers of the deaf battle to
improve the monotonous and unnatural voice inflections typical of the deaf, both
children and adults.
What may be needed is an apparatus which would display the fundamental pitch of
the voice in a simple, clear, and logical way. At once the problem arises that
the human voice is composed of many tones: the fundamental tone and a series of
other tones called upper harmonics or partials. Only the fundamental tone gives
the actual musical pitch. The others give quality or timbre.
Although the energy of the fundamental tone has often only a small fraction
of the total energy of the sound, the ear of a hearing person has usually no
difficulty in separating it from the higher harmonics and so recognising
typical speech tunes and copying them. What is so easy for the sophisticated
human ear to do, however, presents considerable difficulties for any man-made
apparatus.
The problem is thus how to visually indicate the fundamental pitch of
consecutive words or syllables as they are vocalised, however high or low
this might rise or fall, while at the same time automatically eliminating
the unwanted extra harmonics, preventing them from signalling their
presence.
 After
years of research and experimentation, AE Coyne designed and developed an
apparatus which succeeded in doing this. A vertical column of differently
coloured lights, each light representing a different pitch, covered a range of
pitch of 3½ octaves, from the lowest notes in a man's voice to the highest
notes in a child's or woman's voice. The interval between one light and the next
was two semitones. When the deaf child or adult spoke into the microphone, the
coloured lights rose and fell (or
remained in one place) according to the pitch changes (or lack of them) of
the speaker's voice.
 A
logical extension of this was designed: an instrument to help hearing singers to
improve their singing pitch. This model had lights set at semitone intervals,
that is, like the keys on a piano, but arranged vertically rather than
horizontally.
The work carried on. Successful prototype models were built by the family
business and a few were sold to schools for the deaf.
In November 1977, Pat Coyne began the task of building another pitch
indicator and doing research into further developing the system. Today, the
present model is a modernised and improved version of the original design. There
is commercially available equipment on the market which simultaneously displays
all the frequencies of the voice in complex patterns but which requires
considerable training on the part of the user and is not therefore suitable for
children.
The principle chosen as the best for the purpose was the electro-magnetisation
of specially-designed tuning forks. By the use of a
microphone and a purpose-designed amplifier, the tuning forks would
automatically respond to the sounds of the voice nearest to their natural
pitches. The amplifier needed to incorporate vacuum tubes because an
amplifier using a 'solid state' system of transistors, microchips and
printed circuits would not have the ability to energise the tuning forks.
The speaker or singer uses a microphone feeding into the above-mentioned
amplifier which incorporates vacuum tubes (thermionic valves). The sounds of the
voice are translated into electrical impulses whose frequencies
correspond to the frequencies of the vibrating vocal cords.
The output of the amplifier is direct current (d.c.) emanating from the
plate of the last output tube. This circuit flows through solenoids which
enclose one or both arms of each tuning fork. When the amplifier is switched on,
all the tuning-forks are magnetised, and become electro-magnets.
When the sounds of the voice are changed into the electrical impulses
mentioned above, these impulses are imposed on the direct current of the
amplifier's output. The result is a fluctuating d.c. current, which flows
through the solenoids. The tuning fork whose natural frequency corresponds
to the frequency of a particular sound of the voice will respond, that is,
it will vibrate in sympathy.
Each tuning fork is fitted with a weighted reed which bounces when the
tuning fork vibrates. By bouncing, the reed breaks an electrical circuit.
This releases a relay, which, in turn, closes a circuit and causes a lamp to
light. The relay component was designed automatically to cut out the feed to any
units responding to a higher frequency, and so to forbid any upper
harmonic from signalling its presence.
(One should record here that intensive and expensive experiments were made
during the research, in the use of purely electronic 'solid state' circuits
coupled with logic gates, as a possible alternative to electrically operated
relays, but the results were inefficient and disappointing.)
Apart from their precise operation, a certain delay in signalling suits the
human eye, and relays proved to have a natural, very slight lag in operation
and in all respects are thus are ideally suited for this purpose.
A range of 41 semitones (and therefore 41 responsive units) was chosen, to
cater for the lowest notes sung by most male singers and rising to the
highest notes sung by most sopranos or child singers, i.e.: from D (77.6 Hz)
to G (784 Hz). The 41 lights have different colours to enable any change of
pitch to be readily visible, and also so that deaf children are stimulated
to try to make a variety of lights in other colours flash. The lights are
placed vertically at the side of the display, which is a special adaptation
of the 'Great Staff' musical notation scale. Each light is labelled with its
musical name as well as its scientific frequency.
Why were smaller intervals not chosen? Apart from the fact that a greater
number of units would then be needed, thus increasing the cost, semitone
intervals, as on a piano and as in all sheet music, are familiar to most
people, and therefore logical. Most hearing people, even if non-musical, can
distinguish a difference in pitch of one semitone.
Incorrect pitch: Singing slightly sharp or flat by an amount of less than a
semitone causes the light belonging to the nearest unit above or below to
flicker, as opposed to being illuminated steadily.
 Some
of the recent technical improvements: A system of fine adjustment of
the pressure of the bouncing reed on the tuning fork was added, and this has
made an even response easier to attain. The operation of the relays was greatly
improved by the incorporation of 'high speed diodes' across their solenoids. The
output circuit of the amplifier was revised to allow a more balanced and more
powerful energisation of the tuning fork solenoids.
The Coyne Voice Pitch Indicator exists only as a prototype model, located in
South Africa. Could it be produced commercially in this country, or in other
parts of the world? Manufacturing it would need a relatively modest
financial outlay. However, components such as the special tuning forks,
their solenoids, and their reeds are not available on the market. They would
have to be made, and the skills to do this would have to be learned. The
supply of the relays and the special amplifier with its matching microphone
seems practicable as most of the components are available commercially.
More information:
Patrick Coyne
P.O. Box 931
Hyper by the Sea
4053
Tel: 031-5723077
E-mail: coynep@telkomsa.net
Related articles:
 A
Bridge for the Problem of Deaf Telephony
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