Electroglottography & Inverse Filtering Procedures are the important procedures for the analysis of the voice. Here is o

1. Topic – Electroglottography & Inverse Filtering Procedures
Submitted To – Mrs. Garima Dixit Garge
Presented By – Mr. Piyush Malviya

2. ELECTROGLOTTOGRAPHY -
 Electroglottography (EGG) is a noninvasive technique for obtaining an estimate of vocal fold
contact patterns during phonation.
 A gold electrode is placed on each side of the thyroid cartilage at a level corresponding to
the position of the vocal folds.
 A weak high‐frequency electrical current is passed between the electrodes.
 As vocal fold contact area changes, there are changes in the electrical resistance between the
electrodes.
 When the glottis is opening or open, resistance increases; when the glottis is closing or
closed, resistance decreases.
 The resulting Lx waveform, called an electroglottogram or laryngogram, reveals summary
information about vocal fold contact over time.
 The EGG can be used to visualize various types of voice quality. For example, Figure 6.14
shows electroglottograms for a prolonged /i/ vowel produced with a normal voice quality, a
breathy voice quality, and a hoarse voice quality.

3.  Electroglottography (EGG) is a technique for the measurement of vocal fold contact area based
on the principle that tissue conducts current.
 A high frequency low current signal is passed between the vocal folds via electrodes located
on the externa neck over the thyroid lamina.
 When the vocal folds touch, greater current flows than when they are open.
 There 13 a proportional variation of current when the vocal folds are less than maximally open
or closed.

5.  Electroglottographic recordings can be used to determine when the vocal folds are closed and
how fast they are closing.
 If carefully interpreted, it is possible to determine characteristics of the opening of the vocal
folds from an electroglottographic recording.
 Devices to record the electroglottographic signal are readily available.
 Currently these include the Voiscope and Laryngograph (Laryngograph, Ltd.), the single
channel SCI or the dual channel MCZ-l (Glottal Enterprises), and the unit from F] Electronics.
 Electrical output of the electroglottograph can easily be converted to hard copy using
oscillograph or similar graphic recording device, or from a computer generated display.
 The literature on EGG is primarily qualitative in nature, based on interpretation of the
waveform.
 Several studies have related the shape of the EGG waveform to the underlying physiology of
vocal fold vibration.
 Information has also been reported on characteristic waveforms in patients with vocal
pathology.

6.  There have been many attempts to quantify the electroglottograph signal.
 EGG reflects the state of the vocal folds in a way that can be easily demonstrated and
interpreted to patients.
 However, a limitation of the technique is that it cannot be used with all patients.
 Because the technique depends on vocal fold contact, the signal is considerably diminished
or even absent in patients with lack of good contact, such as those with unilateral paralysis, or
aphonia.
 It may also be difficult to obtain a clear waveform in the presence of severe hoarseness.
 The thick or large necks of some patients hinder transduction of the current and result in a
poor EGG tracing.
 Manufacturers of EGGS have greatly enhanced its clinical value. For example, the MCZ-l EGG
made by Glottal Enterprises uses two identical circuits and two sets of electrodes.
 The output of each electrode pair is compared and displayed 'on a meter. When the meter
reading is O, the output of the two channels is identical and the vocal folds are centered
between the two electrode pairs.
 This simple monitoring device helps to insure the proper placement of the electrodes and an
optimal EGG signal.

7. INVERSE FILTERING PROCEDURES –
 In the inverse filtering procedure, the voice signal emitted at the lips is analyzed to
remove the resonant effects of the vocal tract, producing an estimate of the waveform
produced at the waveform.
 According to the acoustic theory of speech production, speech is the product of a sound
source and a filter.
 That is, the sound output of the vocal folds is modified by the resonant characteristics of
the vocal tract.
 If the resonant characteristics of the vocal tract are known, it should be possible to
retrieve the characteristics of the output of the vocal folds from the orally emitted
speech signal.
 Inverse filtering has been performed on the acoustic sound pressure waveform.
 We have used the airflow waveform for inverse filtering of normal and voice-disordered
subjects.
 We routinely record the EGG signal simultaneously with the inverse filtered airflow signal
to extract information about the vibratory characteristics of the vocal folds during the
complete cycle.

8.  The techniques complement each other in that airflow will often not be present during
the closed phase of the vocal folds, but the EGG provides information about vibratory
characteristics of the vocal folds during that phase.
 Thus, with both techniques, we are able to obtain a more complete picture of vocal fold
vibratory characteristics during speech.
 The result of inverse filtering the oral airflow waveform is called a flow glottogram and an
example is shown in Figure 7.13.
 Four channels are collected directly into the computer using CSpeech.
 These are the (a) acoustic waveform, (b) raw oral airflow waveform, (c) EGG waveform,
and (d) intraoral air pressure pulses associated with the stop plosives in the utterance
(not shown in Figure 7.13 but see Figure 7.14).

11.  The oral airflow waveform is inverse filtered using CGlott, a computer program
separate from but complementary to CSpeech.
 The result is the inverse filtered or flow glottogram shown in Figure 7.13.
 Collection of electroglottographic and inverse filtered airflow waveforms is routine
in our clinic.
 The following measures are obtained from computer-assisted analysis of the
waveform: (a) each cycle’s minimum (or leakage) and ac airflows, (b) the ratio of the
time of the airflow pulse relative to the total period (airflow duty cycle), (c) the ratio
of the closing and opening slopes of the airflow pulse (airflow speed quotient), (d)
the ratio of the open time to the total period of the electroglottographic waveform
(abduction quotient),(e) the closing time of the electroglottogram waveform, and
(f) lung pressure.

12. REFERENCES
 Boone, D. R., McFarlane, S. C, Von Berg, S. L. & Zraick, R, I. (2013): The Voice and
Voice Therapy. (9th Ed.). Englewood Cliffs, Prentice-Hall, Inc. New Jersy.
 Colton, R. H, Casper, J. K. & Leonard, R. (2006). Understanding voice problems.
Baltimore: Williams & Wilkins.