Speech Transmission Index.
WinAudioMLS can perform objective speech
intelligibility measurements an addition to the room analysis module (energy decay curve and
reverberation time). WinAudioMLS calculates the speech transmission index (STI) and (room
analysis speech transmission index) RASTI according to IEC 60268-16.
The calculation is based on a measured impulse response. WinAudioMLS
calculates the modulation transfer function (MTF) with 7 octave filters (125Hz
250Hz 500Hz 1000Hz 2000HZ 4000Hz 8000Hz). The MTF is evaluated at certain modulation frequencies 0.6Hz..12Hz.
For each octave band 14 modulation frequencies are used. These values are averaged and
weighted to compute the final STI value. The STI ranges between 0 (poor) and 1 (excellent).
RASTI is a simplified version of STI. It uses only 2 bands (500Hz and 2000Hz).
WinAudioMLS displays the MTF for all bands at the specified modulation frequencies in a table.
This table can be written to a text file for storage or further analysis.
WinAudioMLS can use the impulse response measured with its internal MLS module for STI analysis. In addition, you can also load
an external impulse response from a simple text file.
The complete STI calculation is lightning fast, it takes less than a second for all bands.
On the product CD you will find some sample impulse responses:
|
sti_ideal.txt |
single impulse, no noise , ideal transmission STI=1.0 |
|
sti_SNR0dB.txt |
single impulse, SNR=0dB STI=0.5 |
|
sti_noise.txt |
noise only STI=0.0; |