FONIX® 8000 - Frye Electronics

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92 FONIX 8000 Hearing Aid Test System Technical details The digital processing delay measurement is taken by sending a short impulse from the sound chamber speaker to the hearing aid. The FONIX 8000 Test System microphone collects information from the hearing aid for 20 milliseconds from the time the impulse is delivered. This information is a series of numbers of varying amplitudes. The FONIX 8000 Test System finds the maximum peak amplitude of the resulting information. Since the impulse response of a hearing aid is not always simple, the analyzer also checks for any peaks occurring before this maximum peak. If a smaller peak exists, and it has an amplitude of at least 50% of the maximum peak, the time of the smaller peak will be considered the processing delay point. Otherwise, the time of the maximum peak will be considered the processing delay point. The 8000 Test System delay is subtracted from this delay point in order to form the actual aid processing delay time. (The 8000 Test System delay is determined during the sound chamber leveling process.) The data collected in the digital processing delay measurement is displayed in graphical format as amplitude vs. time. A dashed vertical line is placed at the calculated delay point. The numerical value is also displayed. A second dotted vertical line shows the 8000 system delay for reference. 4.1.2 Signal Phase The signal phase measurement is a test of the “pushing” and “pulling” of the amplified sound of the hearing aid. Vibrations in the air create sound—these vibrations can be thought of as air pushing and pulling against the ear. If sound goes through a hearing aid, the hearing aid might cause a phase shift, turning a “push” of the sound wave into a “pull.” This isn’t necessarily a bad thing; there may be good reasons for a phase shift of the sound wave. The components of a custom hearing aid are usually wired by hand. The receiver is typically wired into the amplifier in such a way that it may or may not cause a phase shift of the signal. If care is not taken, it’s entirely possible to wire one hearing aid of a custom binaural set one way, and wire the other aid in the opposite way. This could cause one of the hearing aids to be “pulling” while the other aid is “pushing,” resulting in strange sound quality for the hearing aid wearer. We propose that it could be very important to check the signal phase of the hearing aids when fitting a client with a binaural set in order to ensure that the aids are working together as a team. Technical Details The signal phase measurement works by generating a 1 kHz cosine wave, turning it into a test signal and delivering it to the aid. The cosine wave signal is offset at the time of generation so that it starts at the baseline (the zero point).
Advanced Coupler Tests 93 It then continues through a complete cycle and terminates when it reaches the baseline again. This signal, although consisting of only a single pulse, contains very few frequencies above 1 kHz and is one millisecond wide at its base. The data collected from this measurement is displayed in a graphical format 20 milliseconds wide. The system delay and the digital processing delay are noted for reference on the phase graph in the form of vertical lines. 4.1.3 Procedure 1. Press [F3] in the Opening screen to enter the Advanced Coupler Navigation screen. 2. Press [F4] in the Advanced Coupler Navigation screen to enter the Enhanced DSP screen. 3. Set up the hearing aid for testing in the sound chamber. See Section 3.3. Make sure the sound chamber is leveled. 4. Use [F1] to select the desired ear. Figure 4.1.3—Enhanced DSP measurement results 5. Press [START] to perform the delay and phase tests for that hearing aid. If the left ear was designated in Step 4, the results will be shown in the upper two graphs. Otherwise, they will be shown in the lower two graphs.
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Chapter 7 145 The ISTS Test The IST
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The ISTS Test 147 No HL 250 Hz 375
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Appendix A 199 Specifications ACOUS
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Specifications 201 Size: 11.5"W x 1
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Appendix C 209 Calibration There ar
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Calibration 211 6. Thread the probe
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Appendix G 223 Glossary of Terms AG
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Glossary of Terms for the FONIX 800
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Appendix H 229 The FONIX Keyboard A
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FONIX® 8000 - Frye Electronics

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