FONIX® 8000 - Frye Electronics

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40 FONIX <strong>8000</strong> Hearing Aid Test System For the needs of most clinicians, the Standard and Chirp Composite signals are virtually identical. The Standard Composite signal is composed of 79 different individual frequencies that are each generated with a random phase pattern that results in the signal having a crest factor of 10 dB, close to the crest factor of human speech. (If the phase components were not randomized or otherwise changed, and if all the signal components were in phase, the crest factor of the signal would increase to over 19 dB.) The Standard Composite signal is the standard signal used on the 7000 test system, the predecessor to the <strong>8000</strong>. The Chirp Composite signal is another type of composite signal, but with a lower crest factor. The phase of the individual frequency components of the Chirp Composite signal is determined in a way that makes the signal appear to be presented as a “chirp,” or very fast sweep. The Chirp has a crest factor of 6 dB. The Chirp Composite signal is the standard composite signal used on the FP40 and FP35 portable hearing aid test systems. Although the Standard and Chirp Composite signals sound the same to most people, an analysis tool such as Tempus3D will show the difference between them. Both the Standard and the Chirp Composite signals are further speechweighted to agree with the user-selected composite filter (described in Section 2.3.2.3.) 2.3.2.5 Composite source levels The Composite signal (and its Digital Speech counterpart) is a complex signal consisting of 79 different frequency components. When you set the source level of a composite signal (50 dB, 60 dB, etc), you are actually setting its overall energy, known as the RMS (root-mean-square) of the signal; you are NOT setting the amplitude of the individual frequency components. The actual amplitude of each of frequency of the Composite signal is less than the overall RMS of the signal. See Figure 2.3.2.5 for an example of the SPL levels of each frequency of the Composite signal with an RMS of 70 dB. Be aware of this difference, especially when viewing frequency response results in overall amplitude of dB SPL.
General Operation 41 Figure 2.3.2.5: ANSI weighing of the Composite signal at 70 dB SPL RMS 2.3.2.6 Digital Speech technical details The digital speech signal works by turning the composite signal on for a set period of time, taking a measurement, turning the signal off for a random period of time, and turning the signal back on again. This sequence is repeated until the test ends. The signal “on” time takes a minimum of 60 milliseconds. This includes the time to turn the signal on, take the measurement, and turn the signal off. Some aids may require an additional delay before the measurement is taken in order to allow their circuits to settle. This additional delay time can be changed in the MISC MEAS delay setting that is available in the local menu of the measurement screens and in the Setup Menu. The MISC MEAS setting is automatically adjusted according to the aid type selected. This setting is added to the 60 ms minimum measurement time. The default settings are: Linear: 20 ms AGC: 100 ms ADAPTIVE: 200 ms The signal “off” time is random between 100 and 300 milliseconds. This time is not controllable by the user.
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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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150 FONIX 8000 Hearing Aid Analyzer
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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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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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