Audioscan Verifit 2 Manuel d'utilisateur télécharger pdf (Page 61)

Verifit

User's Guide Version 4.2 © June 2015

the instrument on and follow the fitting procedures presented previously in this section. It is necessary to

repeat the Equalize procedure whenever the client or nearby objects are moved.

Verifying Frequency Compression/ Frequency-Lowering

Hearing Instruments in Speechmap

Frequency lowering is used when it is not possible to amplify the high frequency components of speech

sufficiently to raise them above threshold. In this case, the high frequency components may be shifted to a

lower frequency with a better hearing threshold where the available gain will render them audible.

Four modified versions of a calibrated speech test stimulus (Speech3150, Speech4000, Speech5000 and

Speech6300) are provided in Speechmap to assist in verifying and adjusting frequency lowering devices. In

each of these modified test stimuli, the 1/3 octave band levels above 1000Hz are reduced by 30dB, except for an

isolated 1/3 octave band centered at the frequency indicated in the selected test stimulus’ name. With these

reduced band levels, the resulting LTASS produces a distinct 'cavity' between 1000Hz and the selected high

frequency band, as seen below for the FM Boom test signal.

To test frequency-lowering:

1. Right click to show the home menu and choose Speechmap from either the On-ear or Test box columns.

2. Program the hearing instrument so that the frequency-lowering feature is inactive.

3. Access Test 1, 2, 3 or 4 by clicking on the appropriate to start that test.

4. Choose Speech3150, Speech4000, Speech5000 or Speech6300 from the Stimulus pull-down menu. Choose

65dBSPL from the Level pull-down menu. Note that only the LTASS is shown for these stimuli and targets

(if selected) have been suppressed.

5. Click to measure and store the long-term signal-averaged result. If the isolated band does not appear in

the Test 1 curve, it may indicate that the hearing aid has no gain at the selected band frequency. This does

not mean that the hearing aid will be unable to transpose the band to a lower frequency when frequency

lowering is enabled.

6. Program the hearing instrument to activate the frequency-lowering feature.

7. Click another and select the same stimulus and stimulus level used in Test 1.

8. Click to measure and store the long-term signal-averaged result.

9. The isolated band should now appear at a lower frequency and should reach or exceed threshold at its new

location as shown below. Note that the 'cavity' between 1 kHz and the isolated band may be partially or

completely filled in by noise within the hearing aid which will make the isolated band appear less distinct in

the test curves.

10.Once the frequency-lowering properties of the hearing instrument have been verified, use one of the

calibrated speech stimuli to verify aided speech audibility or target match (as described elsewhere in this

section) for frequencies below the isolated band.

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Audioscan Verifit 2 Manuel d'utilisateur Page 61