Speech Transmission Index

Speech Transmission Index, short STI is a measure of speech transmission quality. The absolute measurement of speech intelligibility is a complex science. The STI measures some physical characteristics of a transmission channel (a room, electro-acoustic equipment, telephone line, etc.), and expresses the ability of the channel to carry across the characteristics of a speech signal. STI is a well-established objective measurement predictor of how the characteristics of the transmission channel affects speech intelligibility.

The influence that a transmission channel has on speech intelligibility is dependent on:

  • the speech level
  • frequency response of the channel
  • non-linear distortions
  • background noise level
  • quality of the sound reproduction equipment
  • echos (reflections with delay > 100ms)
  • the reverberation time
  • psychoacoustic effects (masking effects)

Read more about Speech Transmission Index:  History, Scale, Nominal Qualification Bands For STI, Standards, STIPA, See Also

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