Speech Stimuli/Ists; Composite Signals/Icra; What Stimulus To Choose - Interacoustics Affinity 2.0 Additional Information

2.0
Affinity Additional Information
2.6.6.2

Speech Stimuli/ISTS

Speech is likely to be the most important signal to the hearing aid user in his or her daily life. Therefore, if
you wish to verify if speech sounds are audible there is no better stimulus than speech. Furthermore, speech
signals challenge the hearing aid since they have quick change in amplitude, frequency, and phase.
ISTS (International Speech Test Signal) is an internationally recognised test signal. It was created based on
the need for a standard test stimulus that included all the relevant properties of speech and allowed for
reproducible measurement conditions. It is created from natural recordings of speech which is non-intelligible
due to remixing and segmentation. The signal reflects a female speaker for six different mother tongues
(American English, Arabic, Chinese, French, German, and Spanish) reading "The north wind and the sun".
The ISTS is shaped according to the LTASS (Long Term Average Speech Spectrum) standards (Holube et
al. 2007).

2.6.6.3 Composite Signals/ICRA

Artificial signals without significant variation in intensity and frequency can also be used in order to test
hearing aids in the frequencies of speech. These are called speech spectrum shaped composite signals and
have the same long-term spectral characteristics as speech.
The advantages in such signals are that you are able to test many frequencies in a short time and that
interactions among frequencies can be tested.
The ICRA signals (International Collegium of Rehabilitative Audiology) are examples of composite signals.
They are a group of test signals developed by the HACTES group (Hearing Aid Clinical Test Environment
Standardisation) in order to be able to do reliable measurements on non-linear digital hearing aids. They
represent a number of speech weighted noise signals composed with spectral and temporal characteristics
similar to those that are found in speech signals and babble noise. (www.icra.nu).

2.6.6.4 What Stimulus to Choose?

Which stimulus to select depends on your focus and the individual clients' complaints.
If, for example, you are seeing a client who complains about not being able to hear his wife, you may want to
use the ISTS.
If the client is having trouble when more than one person is speaking, the ICRA 6pbl (or one of the other
signals with multiple people speaking) may be selected.
If you wish to look at the effects of - noise reduction, a noise signal such Pink Noise may be the appropriate
choice.
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