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- 50 db target, they will quickly adjust the gain for soft sound or compression

threshold. And finally to match the 80 db or louder input target the commission

will adjust the gain for loud sound or compression ratio in their software. Now

let's look at using relay insertion gain with the hybrid sound processor to achieve

and match target sound level or DSL. To do this we would use our custom sound

4.2 software and we would adjust the overall gain or the gain on the individual 8

channel to try and match our 65 db input target, so to match our target for an

average speech level. In the current version of the programming software we do

not have the option to adjust for the soft and loud input codes however you do

have the option to select wide dynamic range compression to ensure that those

loud sounds are comfortable, and not amplified as much as average or soft input.

For hearing losses that require more gain, you also have the option to increase

the MPO over all or in the individual channel for you to achieve that requiredgain. So as we mentioned there are three prescriptions available if you have no

particular preference or any, then by default the hybrid prescription with wide

dynamic range compression will be selected and this is a good starting point

because as I mentioned the prescription was specifically designed and developed

for hybrid devices rather than being a conventional hearing aid prescription. The

software will also let you use the hybrid prescription or any of these prescriptions

with linear or wide dynamic range compression and I will now just go through

both of those options for you and when you might want to use linear v/s widedynamic range compression in your hybrid fitting. Linear amplification combined

without foot compression, what we have when we choose this option in the

custom sound software is a strategy that amplifies all inputs equally. So it

amplifies soft moderate and loud sound by the same amount until it reaches the

output limiting of the hearing and obviously the output limiting is fixed to ensure

that loud sounds are comfortable and there is no discomfort or hearing aid

damage. When might you choose linear amplifications? Sometimes when you

have recipients with these very high gain requirements, it is an option to move to

linear to make sure you can provide efficient gain. The other option you have in

custom sound software is to choose wide dynamic range compression and this

type of compression provides different amounts of gain depending on the level of

the input signal. So this time what you will see is softer sounds are amplified more

than louder sounds and what this enables is a wide range of input level to be

made more audible within a narrow range of residual hearing and it also reduces

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the need for manual volume control adjustment. This type of option is selected

often for clients with tolerance or recruitment issues; specifically we would really

recommend you selecting the wide dynamic range compression in the fitting

software at all times unless you require much more gain for a more severe loss.

So now lets look at the clinical fitting of the electrical fitting parameters. Now

typically in the studies, in the literature we say that the majority of electrical

parameters selected for stimulation such as the sound coding strategy stimulation

break mode come with, they are generally the default settings that are being

determined by the implant system. So typically these are not varied in the

literature. There is however one parameter that has been widely varied and this is

the acoustic to electric cross over frequency and this is the frequency at which

stimulation changes from acoustic stimulation to electric stimulation. In the

literature the crossover has been derived in a number of ways, one common way

is being to look at the unaided audiogram and decide the point at which acoustic

hearing is no longer been official so this is the unaided audiogram based decision.

And this has resulted a number of different crossover frequencies being selected,

from frequencies at which the hearing threshold the 6065, 8085 db on the

audiogram. Other ways in which the crossover frequencies is being decided is

through individually based pitch matching experiments, x-rays these sorts of

methods are actually much more time consuming and less typically used to

determine the cross over frequency. So in the custom sound programmingsoftware you have the choice to select the cross over frequency and you also have

the option to overlap or not overlap the electrical and acoustic stimulation. So by

non overlapping we mean that the low frequency information is only presented

by acoustical stimulation and the high frequency is only presented by electrical

stimulation.