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The speech-reception threshold (SRT) is attained

when the LTASS is at threshold (approximately - de-

pending on test material and the individual). These

scenarios are shown in Figures 10 - 12 which follow.

It should be noted that analysis methods which use

shorter time periods produce higher peak levels and

signicantly dierent speech envelopes. In order to

produce results that can be directly compared to mea-

sures of threshold (and UCL), the analysis time period

needs to approximate the integration time of the ear.

Although this varies with frequency and individuals,

a value between 100 - 200 ms is likely. The Verit and

RM500SL use a 128 ms analysis time period as an ap-

proximation because it also has considerable historic

support.

Because the spectrum of a speech signal varies with

time, it is necessary to average measurements over

several seconds to obtain a stable, repeatable result.

However, the eects of adjustments to hearing aid pa-

rameters need to be seen quickly in order to be useful

for optimization. To resolve these conicting needs,

speech signals are rst presented in a repeating loop

with a sound-eld equalization test prior to the start

of each passage. A running calculation of the short-

term speech envelope and average is performed on

2 - 3 seconds worth of data and is displayed in real

time so that the eects of adjustments to hearing aid

parameters are easily viewed. Pressing the Continue

key causes the passage to restart and run in its entire-

ty. The envelope and average are calculated over the

full passage to provide stable and repeatable data.

When using live speech as a test signal, a “Freeze

curve” function is available to capture the short-term

spectra for examination and counseling purposes.

Figure 9: Example of speech envelope and LTASS

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