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Past, Present and Future of STI Herman J. M. Steeneken (www.steeneken.com).
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Past, Present andFuture of STI Herman J. M. Steeneken (www.steeneken.com)
Past: STI (1971, 1980), Envelope Spectrum (1972), MTF (1975), RASTI (1979), prediction by ray-tracing(1981), IEC 60268-16 (1988, 1998)Present: Revised STI (1992, 1999, 2002), STIPA (2001), IEC 60268-16 (2003), ISO 9921 (2003)New and Future: Binaural STI, improvement measurement STI from speech signal, non-native speech, vocoders
Assessment Methods • Subjective assessment with subjects (speakers and listeners): representative, limited reproduction, no diagnostics, laborious • Objective assessment based on physical properties (measurements): reproducible, diagnostic, fast • Objective methods allow prediction of system performance: design tool
Matrix for seven MTF’s 1 Hz 3 Hz 10 Hz X
Relation Noise and Band-pass limiting S.d.= 4.4% Male speech
Embedded CVC words: versta des over en nu fijs uit het woord zek einde noteer lal punt “Semi random” combination of: 17 initial consonants 15 vowels 11 final consonants
Relation AGC and echoes S.d.= 6.9 % Male speech
Full STI (STI-14 and limited modulation frequency range STI-3) STI-14 • Seven octave bands • 14 Modulation frequencies • Random envelope for octaves not under test STI-3 • Seven octaves • 3 Modulation frequencies (1.0, 3.15, and 10 Hz) • Random envelope for octaves not under test
RASTI (Room Acoustics STI,1979) Only for person-to-person communication assessment Two octave bands (500Hz and 2 kHz) Complex envelope (4 and 5 mod. freq.) see Acustica 1984, IEC 60268-16
STI-PA (STI Public Address, 2001) Assessment of Public Address including: acoustic environment, band-pass limiting, overload dis- tortion Seven octave bands (125 Hz and 250 Hz merged) Complex envelope (2 simultaneous modulation frequencies per band) see IEC 60268-16
Future • Binaural STI • Improvement using Speech as test signal • Non-native talkers and listeners
Future: Binaural STI (I) Use artificial head and perform simultaneous measurement on both ears Select highest performance (best ear selection) Use cross correlation approach for 500, 1000, and 2000 Hz.
Conclusions • STI predicts the speech intelligibility for many types of distortion: noise, band-pass limiting, non-linearity's, temporal, vocoding, non-native speech, and binaural hearing. • Improvements (measuring methods or scope) of STI will not change the qualification ranges. • STI is an international standardized method (ISO9921, IEC 60268-16) and used for many national standards.