2. Getting the Most out of FM amplification Presentation to Clarke School Mainstreaming Workshop, Springfield MA, Oct 2007 Preparation supported, in part, by NIDRR grant #H1343E98 to Gallaudet University.

3. Part 1. Enemies of hearing

4. Distance 7266 605448 Speech  Speech quiet Speech loud Speech loses 6 dB for every doubling of distance

5. SPEECHSPEECH Obscures speech sounds that are weaker than itself Distracts the listener Noise SPEECH NOISE

6. SPEECHSPEECH Obscures speech sounds that are weaker than itself Distracts the listener Noise

7. Obscures speech sounds that are weaker than itself Distracts the listener Noise SPEECH NOISE

8. Distance and noise 7266 60 55 48 Speech  Noise  Speech quiet and lost in noise Speech loses 6 dB for every doubling of distance Speech loud and well above noise

9. Free field Enclosed space Room acoustics - the reverberation effect Room acoustics - the reverberation effect Direct sound Reverberation

10. Noise and reverberation (Data from Pegan, 2007, AuD project) Reveberation only (5%) Noise Only (10%) Noise plus reverberation (23%)

11. Noise and reverberation (Data from Pegan, 2007, AuD project) Reveberation only (5%)

12. Noise and reverberation (Data from Pegan, 2007, AuD project) Noise Only (10%)

13. Noise and reverberation (Data from Pegan, 2007, AuD project) Noise plus reverberation (23%)

14. Enemies of hearing Distance Noise Reverberation Plus sensorineural hearing loss Interactions among the above And don’t forget - rapid speech - unclear speech - accented speech - difficult material - unfamiliar words

15. Part 2. The FM solution

16. Listening via the local hearing aid microphone 60 dB 80 dB Noise 55 dB

17. Listening via a remote microphone and direct audio input 80 dB Noise 55 dB

18. Listening via a remote microphone and FM wireless link Modulator/ transmitter Demodulator/ receiver Basically, we have provided an invisible wire between microphone and hearing aid Basically, we have provided an invisible wire between microphone and hearing aid

19. Part 3. Cautions

20. Caution #1. FM is not magic. The FM link does not add anything to the signal. It only takes away the negative effects of distance, noise, and reverberation. The student hears no better via the FM microphone than he does via his hearing aid microphone when the talker is close by.

21. BUT what happens when we turn on the hearing aid microphone? It depends on the relative gains via the two microphones It depends on the relative gains via the two microphones

22. Caution #2. When Aid+FM is used (the default) - - incorrect balance of the two sensitivities can reintroduce the noise and reverberation that the FM was supposed to remove.

23. 1. Equal output FM gain is 20 dB less than Aid gain S/N = 80/55 S/N = 60/55 Aid gain = +40 FM gain = +20 Aid+FM Output = the higher of the two Speech = 100 dB Noise = 95 dB S/N = 100/95 = 5 dB Benefit of FM = 0 dB Output S/N = 100/75 = 25 dB Output S/N= 100/95 = 5 dB

24. 1. Equal output FM gain is 20 dB less than Aid gain S/N = 80/55 S/N = 60/55 Aid gain = +40 FM gain = +20 Aid+FM Output = the higher of the two Speech = 100 dB Noise = 95 dB S/N = 100/95 = 5 dB Benefit of FM = 0 dB Output S/N = 100/75 = 25 dB Output S/N= 100/95 = 5 dB

25. 2. Equal gain FM gain equals Aid gain (transparency) S/N = 80/55 S/N = 60/55 Aid gain = +40 FM gain = +40 Aid+FM Output = the higher of the two Speech = 120 dB Noise = 95 dB S/N = 120/95 = 25 dB Benefit of FM = 20 dB Output S/N = 120/95 = 25 dB Output S/N= 100/95 = 5 dB √

26. 2. Equal gain FM gain equals Aid gain (transparency) S/N = 80/55 S/N = 60/55 Aid gain = +40 FM gain = +40 Aid+FM Output = the higher of the two Speech = 120 dB Noise = 95 dB S/N = 120/95 = 25 dB Benefit of FM = 20 dB Output S/N = 120/95 = 25 dB Output S/N= 100/95 = 5 dB √

27. Adjusting for transparency (equal gain) 1.Confirm aid fitting (Quiet  audible: Loud  comfortable) 2.Connect FM; set to Aid+FM 3.Mute FM mic or place in quiet spot 4.Measure aid output for 65 dB aid input 5.Place FM mic in test box; remove aid 6.Measure aid output for 65 dB FM input 7.Adjust FM gain until the two outputs match

28. Problems in adjusting for transparency 1.Compression in FM transmitter causes FM gain to change with FM input.

29. Compression of FM signal Compression of combined signal Relative gain via FM and AID changes with changing FM input

30. Problems in adjusting for transparency 1.Compression in FM transmitter causes FM gain to change with FM input. 2.Higher output for FM signal may be uncomfortable if not controlled by compression in aid (i.e., improper fitting). 3.Therefore initial FM-gain setting must be validated behaviorally

31. Caution #3. FM benefit applies only to the talker with the microphone - But comments, questions, and answers from other students are part of the total learning experience

32. TeacherSelfOther student Signal- to-Noise Ratio 25 dB 5 dB With single microphone ((((((((((

33. TeacherSelfOther student Signal- to-Noise Ratio 25 dB With two microphones

34. Caution #4. Psycho-social issues -Intrusiveness -Embarrassment -Self-consciousness -Difference -Hassle-factor

35. Psycho-social issues addressed through: -Student counseling/preparation -Class counseling/preparation -Teacher/staff counseling/preparation -Instruction/explanation/demonstration -Behavioral data (single-word dictation with and without FM microphone)

36. Caution #5. Monitoring and maintenance -Equipment fails -Formal plan needed for prompt detection of problems -Speedy repair -Loaner while waiting -Periodic audiological verification and validation

37. Summary -Enemies of hearing: distance, noise, reverberation -Virtually eliminated by FM microphone at talker’s mouth -For best benefit: 1.FM microphone close to mouth 2.Balance of FM and Aid gain (audiologist) 3.Access to contributions of other students 4.Counseling/preparation/instruction/demon- stration/behavioral data 5.Formal program for monitoring and maintenance 6.Periodic verification and validation (audiologist)