Upload
augusta-parsons
View
213
Download
0
Tags:
Embed Size (px)
Citation preview
Copyright by Linda M. Thibodeau 2005
1
FM SystemsFM Systemsfor School Aged Childrenfor School Aged Children
Linda Thibodeau, Ph.D.Advanced Hearing Research Center
Callier Center for Communication DisordersUniversity of Texas at Dallas
Copyright by Linda M. Thibodeau 2005
2
Supportive informationMay be obtained at the
Website of Linda Thibodeau
www.utdallas.edu/~thib
Copyright by Linda M. Thibodeau 2005
3
Welcome to this lecture on FM Systems!
I hope you will find this information interesting and
rewarding as you learn of the significant differences that can
be achieved with
FM Systems!
Copyright by Linda M. Thibodeau 2005
4
OVERVIEW
1. Rationale for use of FM Systems
2. FM Systems
3. FM Evaluation Procedures
4. Use of FM Systems
Copyright by Linda M. Thibodeau 2005
5
Let’s start with the Rationale for using FM Systems.
Copyright by Linda M. Thibodeau 2005
6
1. Rationale for use of FM Systems
A. Signal-to-Noise Ratio
B. Typical Classroom Noise
C. Audio Demonstration of
Classroom Noise
Copyright by Linda M. Thibodeau 2005
7
A. Signal-to-Noise Ratio
A major problem for all persons with hearing loss is….
Listening in Noise !
The problem is described by the
signal-to-noise ratio or SNR.
The amount of “Signal,” what you WANT to hear
. . .compared to. . .“Noise”,
ANY sound you don’t want to hear.
Copyright by Linda M. Thibodeau 2005
8
In a large group, distance and noise can be a problem.
In a large group, distance and noise can be a problem.
Copyright by Linda M. Thibodeau 2005
9
This results in a poor signal-to-noise ratio.
This results in a poor signal-to-noise ratio.
Copyright by Linda M. Thibodeau 2005
10
i.e. the intensity of the noise at the listener’s ear is greater than the signal of the speaker.
i.e. the intensity of the noise at the listener’s ear is greater than the signal of the speaker.
Copyright by Linda M. Thibodeau 2005
11
A poor S/N ratio is -10 dBA poor S/N ratio is -10 dB
the noise is 10 dB more intense than the signal
80 dB80 dB70 dB70 dB
Copyright by Linda M. Thibodeau 2005
12
A good S/N ratio is +20 dBA good S/N ratio is +20 dB
the signal is 20 dB more intense than the noise
90 dB90 dB
70 dB70 dB
Copyright by Linda M. Thibodeau 2005
13
So...ideally we want to have a positive S/N ratio and a
constant signal level regardless of distance between the speaker and the listener.
So...ideally we want to have a positive S/N ratio and a
constant signal level regardless of distance between the speaker and the listener.
Copyright by Linda M. Thibodeau 2005
14
We can accomplish this by placing a microphone on the speaker and delivering the
sound directly to the listener.
We can accomplish this by placing a microphone on the speaker and delivering the
sound directly to the listener.
Copyright by Linda M. Thibodeau 2005
15
B. Typical Classroom Noise
Optimal noise level for a class with students with
hearing loss would be30-35 dBA,
yet the typical level is about 60 dBA.
Average conversational speech is about 60 dBA, which means the
SNR is often 0 dB!
(ASHA, 2005)
Copyright by Linda M. Thibodeau 2005
16
The optimal SNR for teaching students with hearing loss would be
+15 dB, (the teacher’s voice is 15 dB more
intense than the background noise).However, the typical SNR in
classrooms is only about +5 to – 7 dB!
(ASHA, 2005)
Copyright by Linda M. Thibodeau 2005
17
Effects of Noise on Speech Recognition
Finitzo-Heiber and Tillman (1978) measured the effects of noise and
reverberation on speech recognition scores with 8 to 12 year old
children with
Normal Hearing and Hearing loss .
Copyright by Linda M. Thibodeau 2005
18
In a soundbooth: No Noise, Little Reverberation
Children with Normal Hearing scored
95% - Only missed 5% of words
Children who were Hard of Hearing scored = 83% - Only missed 17% of words
Copyright by Linda M. Thibodeau 2005
19
In a situation similar to a typical classroom:
Normal Hard of
Hearing Hearing
SNR of +12 dB: 83% 60%
SNR of 0 dB: 48% 28%
These results suggest that children with hearing loss may only be hearing about one fourth of speech in a typical
noisy classroom.
Copyright by Linda M. Thibodeau 2005
20
C. Audio Demonstration of Classroom Noise
Click on each loudspeaker to hear:Typical Classroom Noise
A teacher reads a story in a classroom with a typical SNR
Same teacher reads a story inan optimal SNR provided byusing an FM System
Copyright by Linda M. Thibodeau 2005
21
Now let’s look at the operation and design of FM Systems in our
second section of the lecture.
Copyright by Linda M. Thibodeau 2005
22
2. FM Systems
A. Introduction to FM Technology
B. Transmitters/Microphones
C. Receivers/Sound Transducers
D. Cochlear Implants and FM Systems
Copyright by Linda M. Thibodeau 2005
23
A. Introduction to FM Technology
FM Systems use a frequency-modulated signal to transmit the speech through the air similar to an FM Radio station.
The system involves a microphone and transmitter on the speaker and a receiver for the listener with some type of sound transducer.
Copyright by Linda M. Thibodeau 2005
24
Microphone
Transmitter
Receiver
Sound Transducer
All FM systems have these parts-
Copyright by Linda M. Thibodeau 2005
25
1) Speaker talks intomicrophone whichgenerates rapidfluctuations ofvoltage
2) Voltage fluctuations are passed to a transmitting antenna
3) Voltage fluctua-tions produce fluctuations of electric and magnetic fields around the antenna ata specific frequency
4) Electric and Magnetic field fluctuations travel as electromagneticwaves
5) Electromagneticwaves produce fluctuations in voltage at a receiving antenna
6) The voltage fluctuations are amplified
7) A filter selectsthe frequency of interest
FM Transmission Process
8) The voltage fluctuations in that frequency range aresent to the acoustic transducer
9) The transducerconverts the voltagefluctuations intosound waves togo to the ear
Copyright by Linda M. Thibodeau 2005
26
Transmitting Frequencies
Typically each transmitter is assigned a frequency,
also called a channel. These may be coded by numbers,
colors, or letters. The channel component may be
called an oscillator.
Examples:
Number Color Letter Trans. Freq.
#1 Red/Gray A 72.000-72.025
#2 Brown/Gray B 72.025-72.075
There may be as many as 40 different channels used
in a school.
Copyright by Linda M. Thibodeau 2005
27
Now let’s look more closely at the Transmitter/Microphone features….
Copyright by Linda M. Thibodeau 2005
28
B. FM Transmitters/Microphones
Descriptive Categories
1) Microphone Type
2) Microphone Location
3) Channel Options
Copyright by Linda M. Thibodeau 2005
29
Microphone Type:The microphone characteristics can vary.
Omni-directional Microphone-picks up sound from all around
Directional Microphone-picks up sound primarily from the top
Multi-Directional Microphone-picks up sound from all around OR
focused area
FM Transmitters/Microphones
Copyright by Linda M. Thibodeau 2005
30
Microphone Location: All Transmitters are worn on the body, but the
microphone placement may vary. On the Body On the Head On the Lapel On the Cheek (also called Boom mic)
FM Transmitters/Microphones
Copyright by Linda M. Thibodeau 2005
31
FM Transmitters/Microphones
Channel Options on the transmitters:Single, but fixed-Oscillator channel set at the factory and cannot be changed Multi-FrequencyManual frequency selection-Oscillator can be removed and changed to another frequency
Wireless frequency selection-Channel
is changed digitally
Copyright by Linda M. Thibodeau 2005
32
Wireless Channel Changeability
1) Direct Frequency Synchronization-Pressing a button on the transmitter sends a signal to the receiver to synchronize the channelEx. Phonak MLxS with Campus S
2) Automatic Frequency Synchronization-Walking near a plate on the wall that contains transmitter changes the channel to a preset numberEx. Phonak MLxS with Wall Pilot
Copyright by Linda M. Thibodeau 2005
33
Automatic Frequency Synchronization-Students wearing Phonak MLxS walking past Wall Pilot as they enter classroom to get synchronized to the correct frequency for that class.
Copyright by Linda M. Thibodeau 2005
34
OTHER OPTIONS - Transmitters
Programmable-Allows the channels to be set digitally via a connection to a computer.
Audio Input Jack-An input jack for the audio signal from another source such as a tape player, VCR, or computer.
No FM/Low Battery Lights-Alerts the users that the batteries or FM switches should be checked.
Talk Over-Allows the microphone to be activeeven when the transmitter is connected to another audio source such as VCR
Mute Switch-Allows the microphone to bedeactivated so conversations can be private.
Copyright by Linda M. Thibodeau 2005
35
Now let’s look more closely at the Receiver/Sound Transducer features….
Copyright by Linda M. Thibodeau 2005
36
C. FM Receivers/Sound Transducers
Descriptive Categories
1) Type-Relationship to Personal Amplification/Cochlear Implant
2) Receiver Location
3) Channel Options
4) Sound Transducers
Copyright by Linda M. Thibodeau 2005
37
FM Receivers/Sound Transducers
1) Type-Relationship to Personal Amplification/Cochlear Implant
There are two main types with respect to interacting with Personal Devices:
Basic-Does not interface with Hearing aid or Cochlear
Personal-Does interface with Hearing aid or Cochlear Implant
Copyright by Linda M. Thibodeau 2005
38
FM Receivers/Sound Transducers
2) Receiver Location:Some FM Receivers interface with a personal
hearing aid worn at the ear? (i.e.one that the student wears throughout the day)
Students and parents generally like this option!!!
Some are worn:On the Body On the Ear
Copyright by Linda M. Thibodeau 2005
39
FM Receivers/Sound Transducers
3) Channel options on FM Receivers?Single, but fixed-Oscillator channel set at the factory and cannot be changed Multi-Frequency
Manual frequency selection-Oscillator can be removed and changed to another frequency to match transmitter
Wireless frequency selection-Channel is changed digitally by pressing a button on the transmitter that is in closeproximity
Copyright by Linda M. Thibodeau 2005
40
FM Receivers/Sound Transducers
4) Sound Transducers
Two Basic Categories:
Basic System-Child takes off personal hearing aid each day and puts on the FM Receiver that picks up the teacher’s voice AND acts like a hearing aid.
Personal System-Child keeps the personal hearing aid on all day and the FM Receiver is interfaced through one of three arrangements.
Copyright by Linda M. Thibodeau 2005
41
FM Receivers/Sound Transducers
Basic System OptionsButton Earphone with Body-worn FM systemEar Level FM Receiver with limited powerSoundfield Speaker to set on desktop or
mounted on the wallFM Amplifier with Behind the Ear hearing aid
Personal System OptionsNeckloop with Personal Aid on T SwitchDirect Audio Input with Personal AidSilhouette with Personal Aid on T Switch
Copyright by Linda M. Thibodeau 2005
42
Let’s look at some illustrations of these different types of sound transducers!
Copyright by Linda M. Thibodeau 2005
43
Button Earphone with Body-worn FM system
Copyright by Linda M. Thibodeau 2005
44
Basic Ear Level FM Receiver with limited Power
EduLinkby Phonak
For Persons with Normal hearing, Mild loss, Auditory Processing Disorder
Copyright by Linda M. Thibodeau 2005
45
Soundfield Speaker to set on desktop or mounted on the wall
Wall MountedSpeakers
Desktop Speaker
Copyright by Linda M. Thibodeau 2005
46
FM Amplifier with Behind the Ear hearing aid
Copyright by Linda M. Thibodeau 2005
47
Neckloop with Personal Aid on T Switch
Copyright by Linda M. Thibodeau 2005
48
Direct Audio Input with Personal Aid
Copyright by Linda M. Thibodeau 2005
49
Silhouette with Personal Aid on T Switch
Copyright by Linda M. Thibodeau 2005
50
OTHER OPTIONS - FM RECEIVERS
Programmable/Digital-Allows the features of the receiver to be set via a connection to the computer which results in more precise control of the FM signal.
Audio Input Jack-Allows a direct electrical connection to a VCR, computer, or tape/CD player.
No FM/Low Battery Lights-Warning lights to indicate the switch settings and/or batteries need checking.
Microphones-When the FM receiver is not interfaced with a personal hearing aid that has a microphone, a microphone will be needed on the FM receiver to pick up the sounds nearby the student but at a lower level than the teacher’s voice.
Copyright by Linda M. Thibodeau 2005
51
Now let’s consider interfacing FM System with Cochlear Implants….
Copyright by Linda M. Thibodeau 2005
52
D. Cochlear Implants and FM Systems
A child may receive a cochlear implant when they receive no benefit from a hearing aid. After a surgical procedure, they receive sound stimulation through electrical impulses applied directly to the auditory nerve. FM systems can be used with cochlear implants to provide that optimal SNR.
The same FM Transmitters and some of the same FM Receivers can be used.
Electrical Coupling of the FM Receiver to the Cochlear Implant can occur in two arrangements:Patch cords connect FM Receiver to Cochlear ImplantDirect Plug-in of FM Receiver
Copyright by Linda M. Thibodeau 2005
53
Patch cords connect FM Receiver to Cochlear Implant
Cochlear ImplantEar Level Processor Body Worn Processor
FM Receiver
Copyright by Linda M. Thibodeau 2005
54
Direct Plug-in of FM Receiver
Cochlear ImplantSpeech Processor
FM Receiver
Copyright by Linda M. Thibodeau 2005
55
It is very important to evaluate FM Systems to
ensure proper settings for maximum benefit. Let’s
see how that can be accomplished in our third section of the lecture….
Copyright by Linda M. Thibodeau 2005
56
3. FM Evaluation Procedures
A. ElectroacousticB. Real EarC. Behavioral
Copyright by Linda M. Thibodeau 2005
57
A. ELECTROACOUSTIC PROCEDURES
ASHA GUIDELINES FOR FITTING AND
MONITORING FM SYSTEMS (1999)This document provides Recommended Measures to be performed to compare response through amplification settings with and without the FM system.
ELECTROACOUSTIC PROCEDURES
Performed by an Audiologist
Child need not be present, only need child’s
Hearing Aid (HA) and FM System
Very objective, efficient way to set systems
Copyright by Linda M. Thibodeau 2005
58
First step is testing the child’s HA alone.
It is attached to a microphone and a sound is delivered, and the output is measured and graphed.
Copyright by Linda M. Thibodeau 2005
59
Next the FM Receiver is attached and the HA/FM system is evaluated.
Copyright by Linda M. Thibodeau 2005
60
The output curves are compared to verify that Curve #2 (FM + HA) shows that the FM signal will be higher than the Hearing Aid alone signal.
Copyright by Linda M. Thibodeau 2005
61
B. Real Ear Procedures
Settings can also be verified by placing a small tube microphone in the child’s ear canal and measuring the sound level while
1) first wearing the HA alone, then
2) while wearing the HA + FM system1) 2)
Copyright by Linda M. Thibodeau 2005
62
C. Behavioral Testing with FM Systems
Threshold Testing typically not recommended due to lack of significant information
Speech Recognition Testing is more meaningful Without FM System With FM System, with examiner wearing FM
transmitter
Test each arrangement in Quiet and in Background Noise if time permits
Copyright by Linda M. Thibodeau 2005
63
Test Arrangement
Examiner Side of Test Booth Student inside Test Booth
Copyright by Linda M. Thibodeau 2005
64
Behavioral FM VerificationCase Illustration
Third Grader who resisted wearing FM system.Testing done to show him benefits.Hearing Aid Alone
Quiet 90% In typical classroom noise 60%
Hearing Aid with FM In typical classroom noise 90%Quiet 100%
With the FM System, the speech recognition score improved from 60% in noise to 90%!
Copyright by Linda M. Thibodeau 2005
65
We’re now at the fourth, and final section
of the lecture….
Let’s consider some ABC’s of using FM Systems in the Classroom!
Copyright by Linda M. Thibodeau 2005
66
4. Use of FM Systems4. Use of FM Systems
A. Microphone Technique
B. Care and Use
C. Settings for Various Teaching Arrangements
D. Troubleshooting
E. Common Problems
F. Manufacturers
Copyright by Linda M. Thibodeau 2005
67
A. Mic TechniqueA. Mic Technique
1. proper distance 6-8 in from mouth
(unless using boom mic, then 2 in)2. don't stand near noise 3. turn off when leaving the classroom 4. antennae must hang free, not
wrapped around transmitter
Copyright by Linda M. Thibodeau 2005
68
B. Care & UseB. Care & Use
1. clean units with damp cloth 2. if put in prolonged storage - need
even temperature3. annual electroacoustic checks4. daily listening checks5. keep in chargers when not in use
Copyright by Linda M. Thibodeau 2005
69
C. Settings for Various Teaching ArrangementsC. Settings for Various Teaching Arrangements
Copyright by Linda M. Thibodeau 2005
70
Settings on FM Receivers
FM Receivers usually have switches that can be set to send certain signals to the listener:
FM Only-Sends only the teacher’s voice
Environmental (ENV) Only-Sends only the voices picked up by themicrophone on the FM Receiver
FM+ENV-Sends the teacher’s voice and the environmental sounds around the
student, ideally the teacher’s voice is about 10 dB more intense than the ENV signal
Copyright by Linda M. Thibodeau 2005
71
1) Teacher lecture1) Teacher lecture
Set Receiver to pick up FM Only Signal
I think they likeI think they likemy tux!my tux!
Copyright by Linda M. Thibodeau 2005
72
2) Class discussion led by the teacher 2) Class discussion led by the teacher
Set Receiver to pickup FM + Environmental (ENV) Signals
I’m not sureI’m not surethey’re listening.they’re listening.
How To SelectHearing Aids....
Copyright by Linda M. Thibodeau 2005
73
3) Independent work at desk3) Independent work at desk
Set Receiver to pickup up ENV Signals
I’d rather beI’d rather beshopping!shopping!
Copyright by Linda M. Thibodeau 2005
74
4) Group work4) Group work
Set Receiver to pickup ENV Signals
I’d rather beI’d rather befishing.fishing.
Copyright by Linda M. Thibodeau 2005
75
D. Troubleshooting - D. Troubleshooting -
Works best when two people check each component separately and the add components progressively according to the following steps:
Copyright by Linda M. Thibodeau 2005
76
1. check FM receiver in microphone mode (as a body aid)
2. check FM receiver & transmitter in FM mode
3. check FM receiver & transmitter in FM & Microphone mode
Copyright by Linda M. Thibodeau 2005
77
4. check FM Receiver & transmitter & personal aid (boot with loop silhouette)
5. check personal aid alone. 6. annually check each component,
daily check entire system (#4)
Copyright by Linda M. Thibodeau 2005
78
E. Common problemsE. Common problems
1. setting volume controls - must be determined by audiologist
2. matching oscillators between transmitter and receiver
3. setting the mic switch4. neckloops often noisy &
inconsistent signal
Copyright by Linda M. Thibodeau 2005
79
5. changes in frequency response re: to hearing aid alone when using direct
input or neckloop6. access to audiologist who can
monitor7. dead batteries8. broken cords
Copyright by Linda M. Thibodeau 2005
80
F. ManufacturersF. Manufacturers
Web pages are VERY helpful, but do not hesitate to contact manufacturer to ask questions:
1. Phonic Earwww.phonicear.com
2. Telex www.telex.com
3. Comtek www.comtek.com
4. AVR Sonovationwww.avrsono.com
5. Phonakwww.phonak.com
Copyright by Linda M. Thibodeau 2005
81
SUMMARY
The SNR can be significantly improved by using an FM system.
Because there are so many options, the audiologist is responsible for selection and fitting of FM systems and the necessary orientation and counseling.
Any connection of hearing aid or cochlear implant with an FM system should be tested in controlled conditions to determine benefit.
FM systems must be monitored on a regular basis by trained personnel under an audiologist’s supervision.
Copyright by Linda M. Thibodeau 2005
82
Last Minute Advice regarding using FM Systems….
If you have a lot of tension and you get a
headache, do what it says on the aspirin bottle:
"Take two aspirin" and
"Keep away from children."
Copyright by Linda M. Thibodeau 2005
83
REFERENCES
American Speech, Language, and Hearing Association (2005). Acoustics in Educational Settings: Technical Report, ASHA Supplement 25, In Press.
American Speech, Language, and Hearing Association (1999). Guidelines for Fitting and Monitoring FM Systems. ASHA Desk Reference, 2, 151-171.
Finitzo-Hieber, T., & Tillman, T.W. (1978). Room acoustics effects on monosyllabic word discrimination ability for normal and hearing-impaired children. Journal of Speech and Hearing Research, 21, 440-458.
Copyright by Linda M. Thibodeau 2005
84
Acknowledgements
Erin Schafer, M.S.University of Texas at Dallas
Paul Dybala, M.S.University of Texas at Dallas
Gary Overson, M.A. University of Texas at Dallas
Jack Scott, M.A. University of Texas at Dallas
Marcia Crouch, M.S.Plano Regional Program for the Deaf
Amy Popp, M.S.Cochlear Corporation
Sallie Frye, M.S.
Frye Electronics
Helmut ErmannPhonak
Hearing Aids
Copyright by Linda M. Thibodeau 2005
85