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128 ms analysis time period as an approximation 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 effects of adjustments to hearing aid parameters
need to be seen quickly in order to be useful for optimization. To resolve these conflicting needs, speech signals
are first presented in a repeating loop with a sound-field 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 effects of adjustments to hearing aid parameters are easily viewed.
Pressing the Continue key causes the passage to restart and run in its entirety. 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 7: Example of speech envelope and LTASS
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07/05/06
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