glottal enterprises EG2-PCX Manual 9/2006
glottal enterprises
Two-Channel Electroglottograph
and
Microphone Amplifier
Model EG2-PCX
Glottal Enterprises, Inc.
1201 E. Fayette Street
Syracuse, New York 13210
USA
Phone: (315) 422-1213
Fax: (315) 422-1216
Internet: www.glottal.com
INTRODUCTION
Electroglottography is an easy-to-use, non-invasive method of measuring the pattern of vocal fold contact variation during voice production. The electroglottograph (EGG) measures the variations in the electrical impedance of the neck at the level of the vocal folds caused by the variation of vocal fold contact as the vocal folds vibrate. The method uses a pair of electrodes on the neck that apply a small, safe electrical current, and measures the patterning of vocal fold contact area (VFCA).
The Glottal Enterprises EG2 two-channel electroglottographs record simultaneous EGG waveforms at two neighboring neck locations. This patented innovation allows the user to easily verify correct electrode placement and waveform accuracy. Using this multichannel approach not only makes the technique easier to use and more reliable, but also can allow the quantitative measurement of vertical laryngeal movement during voicing.
All EG2-series electroglottographs are battery operated and therefore portable as well as safe. These units offer all of the features you would expect to find on an electroglottograph, as well as providing a few unique ones. The Electrode Placement / Larynx Tracking indicator helps the operator determine the optimum electrode placement without guesswork, while a signal-strength indicator indicates whether the EGG signal is strong enough to be reliable.
INITIAL SETUP
The equipment and accessories listed below are provided by Glottal Enterprises:
1) EG2-PCX electroglottograph unit
2) EL-2 electrodes
3) Electrode Strap
4) Water soluble electrode gel
5) Battery charger
6) 3 foot USB cable
7) Cable having 1/8 mini-phone plugs on each end
8) High-quality electret (capacitance) microphone
The EG2-PCX can be connected to your computer using either the USB cable or the stereo output cable having 1/8 mini-phone plugs on each end. The USB cable would be plugged into the USB jack on the rear panel and the 1/8” phone plug cable would be plugged into the stereo, audio-style output jack on the rear panel. The stereo output jack is wired so that the plug ‘tip’ is the audio (microphone) signal, and the ‘ring’ is the EGG signal. (For this reason, a mono plug will not show an EGG signal.) When connected to a computer equipped with a sound card via a stereo cable, the left channel carries the audio (microphone) signal, and the right channel the EGG.
To record audio along with the EGG waveform, the supplied high-quality electret capacitance microphone is plugged into the XLR jack on the rear panel, or a user-supplied microphone can be plugged into the 1/8” phone jack on the front panel.
Before using the EG2-PCX electroglottograph, the (internal) dual batteries should be initially charged for roughly 2 to 6 hours, 2 hours if the battery-condition light (near the Power switch) shows green with the power switch ON, both to the right and to the left, and 6 hours if either of the On positions results in an amber or red ‘low battery’ signal.
To charge the batteries, plug the charger into the receptacle found on the back of the electroglottograph. Place the battery selector switch in the center "OFF" position. In this position both batteries will be charged simultaneously. A more complete explanation of the battery selector functions can be found later in this manual.
FOR MAXIMUM BATTERY LIFE, DISCONNECT THE CHARGER WHEN THE UNIT IS STORED FOR LONG PERIODS.
Totally discharged batteries are usable after about two hour’s charge and reach full charge when charged overnight.
The battery charger is specifically designed to match the charging requirements of the EG2 and EG2-PC batteries. Do not use any other type of charger unit.
The batteries are standard 6 Volt lead-acid gel cells and are field replaceable by a qualified electronics technician, after removing the top cover.
ELECTRODE INSTALLATION AND POSITIONING
1) Insert the modular plug of the EL-2 electrode cable into the receptacle marked "ELECTRODES".
2) Cover the gold surfaces of the electrodes with a very thin coating of water-soluble electrode gel. (A salt-water solution can also be used to wet the electrodes if no gel is available.)
3) Place the electrodes onto the neck so that they are approximately at the level of the thyroid cartilage and about 3/16 inch (0.5 cm) apart at the front of the neck. The left electrode (from the patient's perspective) typically has red wires going to it. If no color indicator is visible, refer to the picture below for proper orientation of the electrodes before placement on the patient. If placed properly on the neck, the narrow gap separating the gold-plated areas on each electrode should be approximately horizontal (parallel to the Velcro band), and not vertical or diagonal.
4) While having the subject produce a constant, prolonged vowel sound in the pitch range to be tested, adjust the vertical position of the electrodes such that the "Electrode Placement/Laryngeal Movement" indicator is centered on the green LEDs. This should place the electrodes in an optimal position so that small vertical movements of the larynx will have minimal effects on the accuracy of the EGG waveform. (The EGG unit output need not be connected to perform this check.)
5) Once the electrodes have been optimally positioned, the subject can hold the electrodes in place using the thumb and index finger, or by using the strap provided. Either way, be sure that the electrodes are completely in contact with the skin at all times.
6) Connect the output of the EG2-PCX to the recording/display system it is to be used with, if not already connected.
Electrode Cable
Glottal Enterprises electroglottographs are normally supplied with 34mm diameter two-channel electrodes. However, smaller 27mm electrodes may be supplied as an option. Electrodes are backed with Velcro for use with the neck strap. We recommend holding the electrodes firmly in place with the thumb and index finger if this is practical.
We also recommend that the electrodes be cleaned with water between sessions and that the metallic (gold plated) surfaces be covered with a very thin coat of water-soluble electrode gel before each use, or wet with a salt-water solution. (The gel or salt water may not seem necessary in damp weather or with some subjects, but we have found poor waveforms to occasionally result with dry electrodes.) For best channel separation, the insulating strip between the metallic surfaces on each two-channel electrode should be kept relatively free of gel. However this is not critical for acceptable performance.
DESCRIPTION OF CONTROLS and CONNECTORS
FRONT PANEL
(1) Battery Switch and Power Indicating Light
This 3-position rotary switch selects which battery the unit is powered from. With the battery charger plugged into the rear of the unit and the battery switch in the "A" position, battery "A" is being used to power the EGG while battery "B" is being charged. The reverse is true with the switch in the "B" position. With the BATTERY switch in the "OFF" position, the EGG is off, and both batteries will be charged simultaneously. When the unit is on and the battery being used is charged sufficiently, a green power indicating light is seen near the BATTERY switch. The light will change color to amber as the voltage of the supply battery diminishes, alerting the operator to switch to the other battery.
Note: In some cases, the EGG output can degrade slightly with the power light still showing green (just before the amber low-battery light is triggered). If there is any reason to suspect that this is the case, switch to the fully charged battery and look for a change in performance. (This easy way to verify battery performance is one advantage of the dual-battery system.)
Note: The EGG unit can normally be used with the battery charger connected. However it is conceivable that with some power line sources interference may occur that degrades EGG performance. If you suspect that this may be the case, try disconnecting the charger. (If you have a verified instance of such interference occurring, Glottal Enterprises would appreciate hearing about it so that we may alert other users.)
(2) ELECTRODES jack
The ELECTRODES jack accepts the modular plug of the electrode cable. The plug and receptacle become firmly interlocked and can only be disconnected by pressing the release tab on the plug.
(3) Electrode Placement/ Laryngeal Movement indicator
This indicator displays a signal which value varies with the relative distance between the level of the glottis and the midpoint between the upper and lower electrode pairs. For routine clinical use we recommend an electrode placement such that the tracking display is green. With this electrode placement slight vertical movements of the larynx or electrodes will have a minimal effect on the performance of each channel, and each channel output will be only slightly weaker in amplitude than its maximum possible value.
(4) OUTPUT GAIN switches
The EG2-PCX is supplied with a 2-position switched gain control for both EGG and audio signals. In the High position this switch increases the amplitude of the EGG output signal by a factor of eight, and the microphone output by a factor of four (12 dB). For the EGG signal, the High gain should normally be used only when a speaker's neck physiology results in a signal with a reading below the green LED on the SIGNAL STRENGTH indicator with the switch in the LOW position.
Note: An advantage of the switched gain over a continuous gain control is that it allows the user to compare signal levels from various users and ascertain if the signal level is sufficient for a reliable EGG signal. EGG sensitivity in either switch position can be verified by using the LS-1 Larynx Simulator available from Glottal Enterprises.
(5) EGG SIGNAL STRENGTH indicator
The SIGNAL STRENGTH indicator monitors the relative amplitude of the EGG output (the sum of the two EGG channels). Though precise thresholds for signal strength required for proper operation have not yet been determined, a scale reading in the amber area of the indicator with the output gain switch in the High (most sensitive) position may indicate that the output signal is too weak to be relied upon as an accurate indication of the variation of the vocal fold contact area. (A considerably weaker signal may be adequate for applications such as F0 measurements, in which the details of the waveform are not important.)
(6) MICROPHONE INPUT jack – front panel
The 1/8 inch phone jack on the front panel accepts any dynamic microphone or self-powered electret capacitor microphone. If a microphone is plugged in here, the XLR microphone jack on the rear panel is deactivated.
REAR PANEL
(7) MICROPHONE INPUT jack – rear panel
This XLR-style jack can accept any microphone having a XLR connector, however, it is specifically designed to accept the ECM8000 omnidirectional electret microphone supplied with the EG2-PCX. It will supply the excitation voltage required by the microphone.
Note: The ECM 8000 microphone should be held vertically, with the tip about a centimeter from the corner of the mouth. This location will yield a high fidelity signal that can be used either for inverse filtering or spectral analysis. The user is referred to the Glottal Enterprises WaveviewStudent CD for examples of voice analysis by inverse filtering using the EG2 electroglottograph and ECM 8000 microphone. There are a number of spectral analysis programs that permit a comparison with a simultaneous EGG signal, as the software sold by VoceVista.
(8) Data Output USB jack
The Data Output jack connects to a computer having a USB input jack, and transmits the EGG and microphone signals in digital WAV–file format, sampled at 44 kHz. The jack supplies power from the computer to the EG2-PCX’s internal A-D system, however, the power to the EGG circuitry and audio preamplifier still comes from the unit’s internal rechargeable batteries.
(9) SIGNAL OUTPUT Jack
This rear panel stereo 1/8” phone jack supplies in analog form the EGG and microphone signals sent to the internal A-D converter. The signals from this jack can then be monitored on an oscilloscope or sent to an external data acquisition system (for example, if more than two channels of data are to be recorded). The tip of the stereo connecter presents the microphone signal and the ring the EGG signal.
(10) PLAYBACK audio jack
This jack connects to the audio output of the EGG2-PCX internal A-D system. It can be used with headphones or an external audio system for auditory monitoring of a recorded signal. (On many computers, the computer’s internal audio card can also be used for this purpose. However connecting the EG2-PCX via the USB jack will normally disable both the record and playback functions of the computer’s audio system, and the playback functionality would have to be re-enabled. See your computer’s manual to accomplish this.)
(11) Charger input jack and charging indicator light,
Accepts the supplied Glottal Enterprises battery charger. Use only the supplied charger.
Optional rear panel outputs - Other optional outputs, if so equipped, are located on the back panel and may include the following. All will be BNC-type jacks unless specified otherwise.
:
F0 TRIGGER Output
This signal can be used to reliably measure vocal fold fundamental frequency. The jack provides a 0.1 msec positive-going pulse or spike for each glottal cycle, synchronized to the glottal closing phase. The time between pulses is the vocal period T0, and the vocal fold fundamental frequency can be computed as F0 = 1/ T0. Since it provides a signal of uniform spectrum that follows the F0 contour of the speech, the signal at this output is also useful as an input to acoustic voice analyzers that permit pitch-synchronous voice analysis, to certain speech synthesizers, or as a phase-settable trigger for laryngeal stroboscopy.
LARYNGEAL TRACKING Output
This output provides the user with the ability to record the DC voltage that is applied to the LARYNGEAL TRACKING INDICATOR. If recorded on a third channel of an external data acquisition system, this signal can be used for verifying proper electrode placement or for tracking vertical movements of the larynx during speech or singing.