Between- and within-speaker variability of voiceless fricatives in Persian

Fricatives vary acoustically across languages and individuals, with speaker variability shaped by both phonetic and non-phonetic factors. This study examined between- and within-speaker variability in Persian voiceless fricatives (/f/, /s/, /ʃ/, /x/) and how linguistic environments, such as syllable position and lexical stress, affect this variability. A gender-balanced sample of 24 Persian speakers was recorded in two sessions, 1-2 two weeks apart. Acoustic analysis targeted the first four spectral moments and duration. Results showed that center of gravity captured the greatest between-speaker variability, followed by standard deviation, skewness, duration, and kurtosis. Across segments, the alveolar /s/ exhibited the highest speaker-specificity, followed by /ʃ/, /f/, and /x/. Gender-based patterns emerged: for males, the center of gravity and skewness of /s/ were most discriminative, whereas for females, the center of gravity and standard deviation of /ʃ/ were most effective. The labiodental /f/ showed some speaker-specific characteristics only in the male group. Voiceless fricatives in syllable-initial positions demonstrated more speaker-specificity, while lexical stress did not impact between-speaker variability. Results also highlight cross-linguistic differences in the acoustic cues most effective for speaker differentiation and demonstrate that optimal features can vary across speaker populations. Adaptive algorithms are therefore crucial for improving forensic speaker comparison.