Electroglottography (EGG)
Introduction
Electroglottography – the
Research Standard for Noninvasive Measurement of Vocal Fold Vibration and
Assessment of Laryngeal Function
Electroglottography allows
for laryngographic assessment of phonatory function during connected
speech, soft and loud singing. It gives qualitative and quantitative
information about the contact, separation and open phase of vocal fold
vibration and is therefore of great use in the interpretation of
pathological conditions and follow-ups after surgical treatment or
conservative voice therapy. It has proved particularly useful in
assessment and documentation of organic voice disorders.
The key benefit of
electroglottography is a direct non-invasive measurement of vocal fold
vibration without interfering in the normal processes of speaking and
singing.
Before each new
laryngographic examination of vocal fold vibration two electrodes are
placed on the subject's neck at the level of the thyroid cartilage. The
laryngograph detects variation in the electrical resistance of the
current passed between the electrodes. The resistance is produced by
changes in the nature and area of vocal fold contact during phonation.
The electrolaryngographic output from the speaker's voice activity is
displayed as a laryngograph waveform showing horizontal opening and
closing movements of the vocal folds. Many of commercially available
devices make it possible to record an additional signal (sound pressure
waveform) from a microphone, which is synchronized with the
laryngographic output, so that both waveforms can be directly compared
when displayed one on top of another.
lingWAVES EGG module
The lingWAVES EGG module
fits seamless in the modular lingWAVES speech software package. It can
be added as an upgrade to existing lingWAVES modules (eg. lingWAVES
Phonetogram Plus, lingWAVES Voice Diagnostic Center (VDC)) or, if purchased as a new
system, it can be enhanced by the addition of further software modules.
lingWAVES users will definitely benefit working with a uniform and
friendly software user interface for clinical voice analyses.
EGG analyses set with the
lingWAVES EGG module:
Instantaneous multi-parameter voice analysis for daily practice
The new EGG multi-parameter module allows for instantaneous processing
of laryngograph and speech waveform data as well as multi-dimensional
voice analysis at the push of a button. The module has all the important
quantitative acoustic analyses most requested by clinicians, researchers
and practitioners in daily practice. The available analyses build up a
multi-dimensional voice profile that is presented on a complex display
and can be printed for filing.
Real-time display of Lx-waveform
Opening and closing movements
of vocal folds and optionally real-time display of acoustic (sound
pressure) waveform, optional marking of open phases under zoom
magnification and Analysis Open Quotient.
Open
quotient
Open quotient is defined as the ratio between glottal open time and
fundamental period. Displays available: Lx-waveform display with marked
open phases, display of open quotient distribution in a speech sample,
display of a plot of open quotient against fundamental frequency.
High
precision jitter and fundamental frequency measurements
Jitter
results from cycle to cycle variations of the fundamental frequency and
is calculated as the mean period to period variation in the residual
fundamental frequency values.
Vocal
fold period cross plot
Cross plot contains information on the period to
period differences in regards to frequencies. The graph on the down left
shows Frequency 1 against Frequency 2, where Frequency 1 is the
frequency value of the first vocal fold period in any pair of periods
and Frequency 2 is the frequency value of the immediately following
period of the pair. Regular vocal fold vibration (left) gives a clearly
defined diagonal line since successive periods have almost the same
values. For the pathological voice, the shape of a crossplot is more
diffuse than is the case with normal speakers as the range of
variability in period to period coherence is not under the speaker's
control. The graph on the down right shows vocal fold frequency
distribution (pitch range histogram), i.e. the range of frequencies
contained in a sample.
Period
by period amplitude crossplot
Provides an insight on the period
to period differences in regards to amplitudes. The amplitude of one
laryngeal vibration is plotted against that of the next vibration. There
is little deviation from the ideal diagonal line distribution for the
good normal voice.
Multiple image display
Display: All analyses can be variably displayed
and printed for filing.
EGG Hardware
The lingWAVES EGG module can
be used with a number of third-party EGG hardware possessing an
EGG/Audio output for a PC-soundcard. Examples of compatible hardware are
listed below.
You can use the lingWAVES
EGG module either with already available EGG hardware or you can
purchase both our EGG module and a third-party EGG hardware from our
distribution partners.
Clinicians and practitioners
are requested to pay special attention to the medical device
classification of EGG hardware (see below). Contact a medical device
classification consulting service for help.
Want to change from old EGG
systems to lingWAVES?
A smooth change from old EGG
systems to the lingWAVES EGG software is possible with any EGG hardware
possessing an EGG/Audio output for a PC-soundcard, e.g. EG2-PC or EG90.
The analog EGG hardware by Laryngograph Ltd., although not tested for
compatibility, is with high certainty compatible with the lingWAVES EGG
module.
Compatible EGG Hardware
The following EGG hardware
have been tested for compatibility with the lingWAVES EGG module:
-
Glottal Enterprises
EG2-PC
(Official manufacturer information about the
product: "Listed with the U.S. FDA (Federal Drug Administration)
which regulates medical devices. The EG2-PC both run on 6Vdc
lead-acid batteries. The large capacitor is low voltage
and ensures a clean power source. The charger is low
voltage (7.5Vdc) and carries the CE mark. The electrodes
are driven by a 2Mhz digital clock signal. The electrodes
are isolated from this low voltage signal by capacitors and by a
pair of isolation transformers. The EGG units made by
Glottal Enterprises were designed to ensure there is absolutely
no risk of shock to the patient.”)
.
-
F. J. Electronics
Portable Electroglottograph type EG 90,
Specification
.
-
Laryngograph Ltd.
Laryngograph® Processor und Digital Laryngograph® USB
We have not been able to test this hardware for
compatibily with the lingWAVES EGG module. However, we have strong
reasons to assume, since both devices give an analog EGG/Audio
output, that they are suitable for use with the lingWAVES EGG
module.
System Requirements
Windows
Operating System 2000/XP/Vista, min. Pentium IV, min. 512 MB working
storage, sound card, PC loudspeakers, CD-ROM
drive, USB-jack, compatible EGG hardware
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