

                       FA1x Rotary Option Switch Operation
                                   06/12/92 -med

        The option controls on the audiometer can be found on the Hearing 
        Aid Simulator rotary switches. Each switch has three option 
        selections available, OptA, OptB, and OptC. Since the Simulator 
        switch is shared with the option selections, this puts some 
        restrictions on the use of the instrument, and forces some 
        forethought on the use of the switches to select options so that 
        they don't completely restrict the use of the instrument.  

        It should also be noted that since the Hearing Simulator switch 
        is not active except when in Microphone or External, the other 
        five simulator positions can be pressed into service as option 
        selections. The use of an overlay might help in identifying the 
        new switch actions.

        To allow at least one channel to have access to the Hearing 
        Simulator functions even when an option mode is selected, it was 
        decided to split the functions into major option modes and minor 
        option modes. Since most people are right handed, it was decided 
        to make the left switch the major option mode switch. and the 
        right switch the minor option mode switch. 

        A minor option mode consists of selecting specific functions 
        within a selected major option. As an example, with RS232 
        operation selected (a major option), it is desirable to be able 
        to select up to sixteen different indications of the operational 
        state of the instrument. This can be done by using the eight 
        available switch positions on the right Simulator switch. and two 
        states on the left major option switch. With care, the selections 
        can be made to allow the speech selections to fit into the minor 
        option selections.

        There are currently three manual instrument options that can be 
        selected. ABLB, MLB, and SISI. These options are selected with 
        the right option switch. The Left Option switch is assumed to not 
        be in an option position (it must either be in the off position, 
        or in one of the hearing aid simulator positions). 

        OptA is defined as ABLB.
        OptB is defined as MLB.
        OptC is defined as SISI. 

        In all three cases, the option selection will redefine the Pulse 
        push button to enable the indicated mode of operation. This means 
        that when an option is selected, the pulse mode is no longer 
        available. When the Pulse led is off, the instrument will operate 
        normally. When the Pulse led is on, the instrument will operate 
        in the selected option mode. 

        If an invalid (undefined) option is selected,, the Hearing Aid 
        Simulator led next to the switch with the incorrectly selected 
        option will flash to indicate the error.



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        ABLB option:

        The ABLB (Alternate Bilateral Loudness Balance) is normally 
        performed by placing the same tone in both ears at different 
        levels. Typically, the reference ear is set to 20SL (20dB above 
        threshold), and the test ear level is adjusted until the two 
        tones appear to be the same level. In a normal ear, this should 
        be linear. That is, the level in the test ear should be 
        approximately 20SL. If there is a difference, recruitment may be 
        happening. 

        The ABLB option is selected by placing the right simulator switch 
        to Option A. With the pulse led off, the instrument will operate 
        normally. This allows the operator to familiarize the client with 
        the tone signals that will be used. 

        When you are ready to begin the ABLB test, press the Pulse button 
        to turn on the ABLB operation. This causes the left and right 
        channels to be alternately turned off and on at a one second 
        rate. Sound on for 500ms in the left channel followed by sound on 
        for 500ms in the right channel.

        The hearing level switches control the hearing level in each 
        channel. The stimulus switches still operate as normal. To 
        properly run the ABLB test, both stimulus switches must be on. 
        The Stenger mode can be used to operate the switches 
        simultaneously.

        There is no restriction on the input or output that may be 
        selected in the ABLB mode. Tone, noise, or speech may be selected 
        in either channel. The only exception is the right Hearing Aid 
        Simulator is not available since it is being used to select the 
        ABLB option. It is not recommended that speech be used since 
        there is no ramping on the speech signal, which will cause
        poping or ticking sounds when the output is switched on and off. 

        Both stimulus switches must be on to cause sound to appear in 
        both ears. If only one stimulus switch is on, sound will appear 
        in that one ear only at 500ms on, 500ms off when the pulse switch 
        it turned on.

        If it is desired to have the test begin in an exact predefined 
        form, the Stenger mode should be used to cause both channels to 
        operate at the same time. 

        Note that if one channel is mixed into the other channel, you 
        will get two 500ms pulse tones separated by about 100ms in time 
        in the target ear at the levels selected on the level controls. 

        It should be noted that these are only guidelines. The specifics 
        of the test vary depending on who you talk to. Therefore it is 
        important to keep the operation of the option as flexible as 
        possible to allow room for various ways of running the test.




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        MLB option:

        The MLB (Monaural Loudness Balance) is normally performed by 
        placing two different tones in the same ear at different levels. 
        Typically the reference tone is set to 20SL (20dB above 
        threshold), and the test tone level is adjusted until the two 
        tones appear to be the same level. In a normal ear, this should 
        be linear. That is, the level of the test tone should be 
        approximately 20SL. If there is a difference, Recruitment may be 
        happening. 

        The MLB option is selected by placing the right Simulator switch 
        to Option B.  With the pulse led off, the instrument will operate 
        normally. This allows the operator to familiarize the client with 
        the tone signals that will be used. The MLB option works exactly 
        the same as the ABLB option. In fact, internally it is the same 
        with the exception of a minor control difference. 

        Since the audiometer only has one frequency knob, a means must be 
        used to select the reference frequency. This is done initially 
        when the MLB option is selected and any time you press the 
        stimulus button to turn on the reference channel for MLB 
        operation. At the time the MLB option is selected, or the 
        stimulus button is pressed, the current frequency selection is 
        saved internally and used as the reference frequency. 

        Normally the MLB test is performed in one ear with two different 
        frequencies. To do this, one channel's output must be directed to 
        the other channel on one of the output switches. 

        This all seems confusing, but once you get used to it, it is very 
        easy and simple to operate.

        Note that as a side effect of the operation, it is possible to 
        use the MLB mode to operated as ABLB but with a different 
        frequency in each ear. This is done by simply not mixing the two 
        channels. 

        Another side effect is that with the pulse switch off, the 
        audiometer becomes an effective two channel audiometer. With the 
        pulse switch off, the audiometer operates normally with the 
        exception that the reference channel frequency is locked and is 
        only updated when the reference stimulus switch is pressed, or by 
        exiting and re-entering the MLB option.

        As with normal ABLB, if it is desired to have the test begin in 
        an exact predefined form, the Stenger mode should be used to 
        cause both channels to operate at the same time. 

        Note that since both channels must be used for this test, it is 
        not possible to mask the other ear unless it is done with an 
        outside masking source.





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        SISI Option:

        The SISI (Short Increment Sensitivity Index) is normally 
        performed by placing a signal in one ear and periodically 
        increasing the level of the signal by a small amount (1-5dB). The 
        test is done at various levels and frequencies to identify if 
        over sensitivity is occurring. The normal ear usually cannot 
        identify a 1dB step increase in sound. 

        The SISI option is selected by placing the right Simulator switch 
        to Option C.  With the pulse led off, the instrument will operate 
        normally. This allows the operator to familiarize the client with 
        the tone signals that will be used. 

        The SISI test operates by sending a constant tone in one channel 
        and periodically increasing the sound level by adding in the tone 
        from the other channel. The repeat rate is once every five 
        seconds starting with the time that the stimulus button is first 
        pressed. A level shift occurs for 200ms by the amount that is 
        selected in the test channel. 

        The reference channel will output sound at the indicated level on 
        the hearing level switch. The test channel control is redefined 
        to be 1/10th of the indicated reading, and it will be added to 
        the output level of the reference channel when the test channel 
        is pulsed on and the outputs are being mixed. If the outputs are 
        not being mixed, the level control is not redefined, and it's 
        output will be as stated on the control. 

        When mixing, the test channel level is limited to 0.5dB to 6.0dB 
        added to the reference channel. If you attempt to add less or 
        more to the reference signal, the error led on the test channel 
        control will flash.

        A reference signal must be presented when the channels are being 
        mixed. If the test channel is turned on but no reference signal 
        is present, the test channel led will flash and the operation 
        will be inhibited until a reference signal is provided.

        The reference channel will present sound at a constant level. The 
        test channel will periodically add a pulse to the sound output 
        when the pulse button is turned on. 

        The output for one of the channels must be directed to the other 
        channel, otherwise the outputs will appear in separate ears. 

        Note that since both channels must be used for this test, it is 
        not possible to mask the other ear unless it is done with an 
        outside masking source.








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        Test Ear and Reference Ear :

        The MLB, and SISI tests refer to a 'reference' channel and a 
        'test' channel. The Reference channel is the audiometer output 
        that is used as the reference signal during the test. The Test 
        channel is the channel that is normally adjusted during the test. 
        The tests require that the reference and test channels be 
        identified to be able to operate the test. 


        Identifying the reference and test channels:

        For tests which mix the two outputs, the reference and test 
        channels are readily identified. The channel with its output 
        switch set to the transducer is the test channel. The channel 
        with its output switch set to the other channel is the reference 
        channel. 

        For tests which do not mix the two channels, the reference 
        and test channels are determined by the stimulus switches. When 
        both stimulus switches are off, there is no reference. The first 
        stimulus switch turned on will become the reference channel. The 
        other channel then becomes the test channel. If Stenger is being 
        used, the switch that is pressed to turn on both channels becomes 
        the test channel, and the other channel becomes the reference 
        channel.

        The ABLB and MLB tests will start the sound output in the channel 
        which the stimulus button was pressed to begin the test. 
        The sound is presented for about 500ms, then 500ms later the 
        sound is presented in the other channel for 500ms, alternating 
        the output back and forth, 500ms in each channel.

        The SISI test will cause the test channel to pulse for 200ms once 
        every five seconds starting with the initial pulse at the time 
        the test channel stimulus button is pressed. The reference 
        channel will remain on constantly if it's stimulus is on. 

        In addition to the channel pulse operation, in MLB mode, the 
        Frequency is locked in the reference channel at the time the 
        reference stimulus button is pressed. 

        Note that if the channels are not being mixed, it is possible to 
        change which channel is the the reference channel. The locked 
        reference frequency will always appear in the current reference 
        channel. You can change the reference frequency at any time by 
        either exiting the MLB mode and re-entering it, or by toggling 
        the reference stimulus button on and off. 

        You can change the reference channel by either selecting which 
        output is being mixed, or if not mixing channels, by which 
        stimulus button is first pressed after turning off both stimulus 
        switches.




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        The ABLB test:

        The ABLB test does not have a specific test/reference channel 
        identification. The test will begin presenting sound in the 
        channel which the stimulus switch was pressed. 

        The ABLB test alternates output on the left and right channels at 
        500ms per channel when the pulse button is pressed. Both stimulus 
        switches must be on for the ABLB test. If a stimulus switch is 
        not on, that channel will not be pulsed. If channels are mixed, 
        the output pulsing will occur in the indicated output at the 
        levels selected in the associated channels. 

        If the pulse switch is not on, the audiometer will operate 
        normally except that the normal pulse test is not available since 
        it has been redefined to the ABLB test.


        The MLB test:

        The MLB test requires that the test and reference channels be 
        identified because two separate frequencies are used and there is 
        only one frequency switch available on the instrument. The MLB 
        test uses the reference channel identification to determine which 
        channel to lock the frequency. The frequency is locked in at the 
        time the reference channel switch is turned on or the MLB mode is 
        entered. The frequency remains locked while the MLB option is 
        selected even if the pulse switch is turned on or off. It is only 
        changed at the time the reference stimulus switch is turned on or 
        the MLB mode is entered. It can be changed at any time while in 
        the MLB mode by pressing the reference stimulus switch off and on 
        (being sure to identify the reference channel while doing it if 
        it is not inherently identified by output mixing). 

        When not in the MLB option, the frequency is not locked and both 
        channels will be set to the current frequency setting on the 
        frequency dial. When entering the MLB option, the current 
        frequency selection will be locked and can only be changed after 
        than by turning on the reference stimulus switch, or exiting the 
        MLB option to unlock the reference channel frequency.

        It should be noted that the MLB test is nothing more than the 
        ABLB test slightly modified to allow the frequency in the 
        reference channel to be locked. Other than that, the test works 
        exactly the same as the ABLB test. 

        If the pulse switch is on, the output will be alternated between 
        the two channels 500ms in each channel. When the pulse switch is 
        off, the output will remain constant. Single ear testing is done 
        by mixing the two outputs into one ear. Sound output begins in 
        the channel in which the stimulus switch was pressed to begin the 
        test (same as ABLB).





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        The SISI test:

        The SISI test requires that the reference and test channels be 
        identified. When the SISI test is running, the reference channel 
        output remains constant, and the test channel output is pulsed. 
        When the two outputs are mixed, the test channel hearing level 
        control is modified to read at 1/10th the indicated hearing level 
        (i.e. 50db becomes 5dB) and is added to the reference channel. 

        If the pulse switch is off and the channels are not being mixed, 
        or only the reference stimulus is on if the channels are being 
        mixed, the output level will be as indicated on the level 
        switches. If the pulse switch is off, both stimulus are on, and 
        the channels are being mixed, the output level will be equal to 
        the reference channel level plus 1/10th the test channel level. 
        If the pulse switch is on and the test channel's stimulus is on, 
        the test channel will be pulsed on once every five seconds for 
        200ms. The output level control will be as indicated above. 

        When mixing, the test channel level is limited to 0.5dB to 6.0dB 
        added to the reference channel. If you attempt to add less or 
        more to the reference signal, the error led on the test channel 
        control will flash rapidly.

        Operation with SISI option selected:

        Pulse off                   Pulse off               
        Ref stim off               Ref stim on             
        Mixed or separate           Mixed or separate
         =No output                  =Output as indicated
        (Error if test stim on)        constant output
        ----------------------------------------------------------------
        Pulse off                   Pulse off 
        Both Stim on                Both Stim on
        Not mixed                   Output mixed
         =Output as indicated        =Output is ref level
           constant output             plus 1/10th test level
                                        constant output
        ----------------------------------------------------------------
        Pulse on                    Pulse on               
        Ref stim off                Ref stim on             
        Mixed or separate           Mixed or separate
         =No output                  =Output as indicated
        (Error if test stim on)
        ----------------------------------------------------------------
        Pulse on                    Pulse on 
        Both Stim on                Both Stim on
        Not mixed                   Output mixed
         =Output as indicated        =Output is ref level (constant)
           ref channel constant        plus 1/10th test level
           test channel pulsed          pulsed on top of ref level






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