Increasing the Effective Use of High

Increasing the Effective Use of High
International Tinnitus Journal, Vol. 14, No. 2, 108–111 (2008)
Increasing the Effective Use of High-Frequency
Spectrum Tinnitus Therapy
Joshua Vicari,1 Joshua Slane,1 Alan G. Madsen,1,2 and Martin L. Lenhardt1,2
1 Northrop
Grumman Newport News Laboratory and Program in Biomedical Engineering,
Virginia Commonwealth University, and 2 Ceres Biotechnology LLC, Richmond, Virginia, USA
Abstract: A new device and method described here will allow real-time processing of any
audio signal (e.g., from a television set) into a high-frequency tinnitus sound therapy stimulus.
By simultaneously listening to the unprocessed and processed speech, a patient can enjoy the
entertainment while obtaining therapy that appears to be a viable alternative in the treatment
of severe disabling tinnitus.
Key Words: neuroplasticity; sound therapy; tinnitus; UltraQuiet
O
ne of the oldest treatments of tinnitus has been
broadband sound therapy as a masker [1]. This
approach is based on the observation that tinnitus will occur in many individuals at night when the
ambient background is lower. In fact, after briefly entering echo-free (anechoic) or sound-attenuated space, selfgenerated physiological sounds become audible, one of
which is usually tinnitus [2]. A logical consideration
was to elevate masking as a tinnitus treatment. Hearing
aids do this and have proven to be effective in masking
tinnitus.
Not all therapy necessarily employs high-frequency
spectra sound. In one form, an attempt is made to phasecancel tinnitus by applying at the tinnitus pitch sounds
that are phase-shifted. Though clearly no tinnitus-induced
basilar membrane movement can be canceled at 180 degrees out of phase, changing the phase (though not usually 180 degrees) is reported to alter neural tinnitus [3].
High-frequency therapy has proven to reduce tinnitus and alter metabolic activity in brain regions thought
to contribute to tinnitus [4]. For tinnitus relief, this approach requires listening to high-frequency modulated
sound over a period of weeks. The stimulation has a highfrequency musical quality, but effectiveness is not only
based on the spectra but is related to disciplined usage.
We report herein a means to modulate any audio signal in such a fashion to provide high-frequency stimula-
Reprint requests: Martin L. Lenhardt, AuD, PhD, Box
980168, Virginia Commonwealth University, Richmond, VA
23298-0168. Phone: 804-343-1047; Fax: 804-828-4454;
E-mail: [email protected]
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tion. Such an adaptation should increase therapy use and
effectiveness.
DEVICE DESIGN GOALS
We aimed to produce a convenient method of highfrequency sound therapy featuring ease of use. It would
produce a therapeutic mode that would result in increased compliance. The method is adaptable to any
audio-producing electronic source, is reliable, and works
in real time. Additionally, it is wireless-compatible.
METHODS
Subjects
Two 21-year-old engineering students served both as experimenters and subjects. Each exhibited normal hearing in the range of 250–20,000 Hz as measured in a
sound-attenuated booth. Speech discrimination was obtained over earphones mounted in custom audiocup cranials. Cranials are sound-isolating covers for earphones
that were modified to accept the earphones used in this
study. Intelligibility was found to be 100% at 65 dB HL
in quiet.
Stimulus
The tinnitus treatment stimulus was produced using
Kyma Version 6 software with a Capybara 320 Sound
Computation Engine. The stimulus consisted of speech
digitally processed and used to modulate one or two signals in the 10- to 22-kHz range. The processed speech
High-Frequency Therapy
was played through a custom-made amplifier into a
piezoelectric bone conduction transducer. The transducer was held in place on the subject’s mastoid bone by
a headband. The bone conduction transducer was placed
on the right mastoid but was heard binaurally [5]. Unprocessed speech was presented simultaneously through
earphones.
The effects of high- and low-pass filtering on speech
intelligibility were determined. The mean performance
is presented in Figure 1. With increasing low-pass filtering, intelligibility dropped in an expected fashion. The reverse was true of high-pass filtering. The point of equal
intelligibility was determined to be about 1200 Hz.
To prepare the speech for tinnitus therapy, the lowpass filter was set with a cutoff frequency of 6 kHz and
the high-pass filter with a cutoff frequency of 2 kHz.
Thus, the resulting passband was 2–6 kHz. This passband was chosen to minimize intelligibility but also to
capture the envelope fluctuations that are characteristics
of high-frequency consonant sounds. This is considered
the speech analogy to the filter and processed music
used with the UltraQuiet system for tinnitus relief. One
or two carrier frequencies can be used, but the data presented here were obtained with the carrier set at 20 kHz
(Fig. 2A).
The carrier is phase-suppressed in the modulator. The
output of the modulator is the speech passband plus the
International Tinnitus Journal, Vol. 14, No. 2, 2008
Figure 2. (A) The spectrum of the processed speech stimulus
used in this study, which is comparable to that of the UltraQuiet system. Speech from any audio device can be converted
in real time to provide tinnitus high-frequency therapy. (B)
The intelligibility of unprocessed speech and unprocessed plus
processed speech as a function of noise level revealing the
high-frequency stimulation does not negatively alter speech
intelligibility, which is important in using a TV as the therapeutic sound device.
carrier and the speech passband minus the carrier. This
signal is amplified and presented to the mastoid. The
general scheme is presented in Figure 1B. A parallel unprocessed speech line is sent to earphones.
Procedure
Figure 1. (A) Speech intelligibility is determined for various
degrees of low- and high-pass filtering. The objective was to
determine a passband that carried the fluctuations in the
speech spectrum that could be modulated with a low level of
intelligibility in and of itself. (B) The speech passband that is
selected is further filtered (as would be the audio output of a
device such as a television) and then modulated on a highfrequency carrier (e.g., 20 kHz) prior to amplification and delivery to a bone conduction transducer. A parallel unprocessed
line is fed from the device to air-conduction earphones.
The subjects were seated in a sound-attenuated chamber wearing earphones (receiving unprocessed speech)
and a bone conduction transducer on the right mastoid
(receiving processed speech). Two speakers generated
broad-spectrum noise from 20 to 96 dB sound pressure
level (SPL). The subjects listened to either unprocessed
speech with varying degrees of masking (up to 96 dB) or
the combination of unprocessed speech by air conduction
and the processed speech segment by bone conduction
(BC), again in various levels of noise. All speech stimuli
were presented at a listening level (65 dB) comfortable
for each subject. Each subject repeated the word heard.
RESULTS
Perception of unprocessed (natural) speech and unprocessed speech plus processed speech (by BC) was at 100%
correct until the noise exceeded 50 dB SPL. The intelligibility of the unprocessed speech and the unprocessed
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International Tinnitus Journal, Vol. 14, No. 2, 2008
speech plus the processed speech gradually declined as
the noise exceeded the intensity of the speech (70 dB
SPL). The addition of the modulated high-frequency
components of speech (i.e., the processed speech) allowed for better understanding in high noise. At 96 dB
SPL of noise, performance for both was less than 10%,
with the unprocessed plus the processed speech remaining superior (see Fig. 2B). The presence of the processed speech does not lower intelligibility; in fact, it
improves it.
The Capybara 320 Sound Computation Engine was
replaced by wideband multiplication and a summing analog modulator circuit with easy dial-in carrier frequencies (Biosecurity Technologies Inc., Richmond, VA).
This module accepts inputs from any audio device and
outputs to a BC amplifier and transducer (UltraQuiet design or compatible system). All the processing is preengineered in the module. Wireless connection to any
audio device is also possible.
DISCUSSION
Any speech source, live or recorded, when modulated
on a high-frequency carrier, will result in a spectrum
similar to that of the UltraQuiet system developed to
provide tinnitus relief [4,6,7]. This system will convert
any audio listening experience into high-frequency
sound therapy for tinnitus, thus removing the drudgery
of specific recorded therapy. The key is to split the output from the audio device into two channels. One runs to
a loudspeaker or earphone while the other is sent to the
modulator and on to the BC transducer. The subject
wears the transducer and listens to the nonprocessed air
conduction sound directly from a loudspeaker or earphones. The audio device volume control should be sufficient to control intensity.
High-frequency sound therapy is effective in tinnitus
control [4,6,7]. Studies of high-frequency stimulation
for tinnitus prevention are very encouraging in that, in
the cat model, such therapy maintains normal spontaneous auditory neuron firing rates and maintains the cortical frequency map [8–11]. Clinically, this means that the
map can be treated, as it were, by external sound that has
already been found to be a viable treatment modality for
humans with severe disabling tinnitus [4,6,7].
In the strictest sense, the real-time modulator will provide high-frequency masking of tinnitus. More important,
it will provide the stimulation needed for neuroplastic
adjustment by the brain. Neuroplasticity is emerging as
a central factor in severe disabling tinnitus [4]; it is the
process by which the brain changes its neural processing
in the presence of tinnitus, changes that include the balance of inhibition-excitation and establishing new connections in the brain [12–14]. One such change is re-
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Vicari et al.
organization of the auditory cortical map, resulting in an
increase of the tinnitus frequency area in some subjects
[15]. This expansion, of course, increases activity in the
limbic system and other sites in the tinnitus final common pathway [16].
CONCLUSION
A custom module can convert any audio signal, including speech, into high-frequency sound therapy for tinnitus relief. The value of a real-time device is that it can be
used when listening to recreational sources, thereby reducing the need for dedicated therapy scheduling. The
end result should be more efficient use of time and, presumably, more effective tinnitus therapy.
ACKNOWLEDGMENTS
The authors thank Ceres Biotechnology for providing
two processing boards for this research and Biosecurity
Technologies, Inc., for providing access to the modulator board.
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