NTi Audio Acoustilyzer AL1 - Manual (Page 57)

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The detailed test result view of the
modulation indices and individual band
level results is provided on the second
STI-PA measurement screen.
c. Detailed Test Result Readout
STI-PA
Octave Bands
Individual Octave
Band LEQ Level
STI-PA Modulation
Index 2
STI-PA Modulation
Index 1
Error
Detection
STI-PA Modulation Index 1 & 2:
For high speech intelligibility it is mandatory that the integrity of the
transmitted voice signal modulations are preserved. Therefore STI-PA is
based on measuring the MTF (Modulation Transfer Function). This function
quantifies the degree to which the voice modulations are preserved in
individual octave bands. STI-PA determines the MTF by analyzing all
seven frequency bands, each band being modulated with two frequencies,
resulting in the modulation index 1 and index 2