Development and analysis of an International Speech Test Signal (ISTS)

For analysing the processing of speech by a hearing instrument, a standard test signal is necessary which allows for reproducible measurement conditions, and which features as many of the most relevant properties of natural speech as possible, e.g. the average speech spectrum, the modulation spectrum, the variation of the fundamental frequency together with its appropriate harmonics, and the comodulation in different frequency bands. Existing artificial signals do not adequately fulfill these requirements. Moreover, recordings from natural speakers represent only one language and are therefore not internationally acceptable. For this reason, an International Speech Test Signal (ISTS) was developed. It is based on natural recordings but is largely non-intelligible because of segmentation and remixing. When using the signal for hearing aid measurements, the gain of a device can be described at different percentiles of the speech level distribution. The primary intention is to include this test signal with a new measurement method for a new hearing aid standard (IEC 60118-15).