Development and Validation of Persian Speech Test Signal (PerSTS).

Abstract

Background: Digital hearing aids require precise fitting to enable realistic speech processing. The international speech test signal (ISTS) provides a standard reference, yet does not fully capture the phonetic and prosodic features of Persian. This study aimed to create and acoustically verify a Persian version of the ISTS-termed the Persian speech test signal (PerSTS)-to enhance verification accuracy for Persian-speaking users.

Methods: The North Wind and the Sun (NWS) passage was translated into Persian with careful phoneme distribution and natural syntax. Six native female speakers recorded the passage at 44.1 kHz and 24-bit resolution. These recordings were segmented, enhanced, and stitched into 10-15 second sequences that adhered to pitch and spectral criteria. Sequences that closely matched the Byrne female long-term average speech spectrum (LTASS; ±1 dB) and were rated as most natural by linguists were assembled into a 60-second PerSTS. The final audio was calibrated to 65 dB sound pressure level (SPL) and analyzed for its spectral, temporal, and amplitude characteristics in Tehran, Iran (2025).

Results: The PerSTS exhibited spectral peaks between 200-400 Hz and 3-4 kHz, characteristic of female Persian speech. Its LTASS closely matches the Byrne LTASS and ISTS, with minor deviations below 500 Hz and above 8 kHz. The crest factor (16.7 dB) and dynamic range (27.1 dB) were consistent with those of natural speech. Experts rated its naturalness as 4.35±0.28 on a five-point scale.

Conclusion: The PerSTS mimics the acoustic and temporal features of natural Persian speech within International Electrotechnical Commission (IEC) standards, providing a standardized tool for hearing aid verification and audiology.