User manual

123
STIPA
13
STIPA Modulation Ratio mr1, mr2
For good speech intelligibility it is mandatory that the in-
tegrity of the transmitted voice signal modulations are pre-
served. Therefore STIPA 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. The STIPA method determines the
MTF by analyzing the seven frequency bands. Each band is
modulated with two frequencies, resulting in the modula-
tion ratio mr1 and mr2. All indexes together combined with
psycho-acoustic models provide the single-value speech
intelligibility result.
14
Error Detection
The built in error detection helps identifying faulty measure-
ments caused by the amount of impulsive ambient noise.
Such noise influences the accuracy of any speech intelligi-
bility measurement. The error detection checks the follow-
ing:
Invalid modulation indices in individual octave bands (mr1 •
or mr2 > 1.3)
Changes in ambient noise or any impulsive noise dur-•
ing the measurement (by comparing the first half of the
measurement period with the second half)
15
Cycle Reading
The standard IEC 60268-16 recommends measuring the
speech intelligibility two or three times at each measure-
ment position. This reduces potential measurement errors.
The individual cycle readings are listed here.
16
STI-Average
Calculated average of the recorded cycle results.
17
Difference
Difference (Max – Min) of the of the recorded cycle re-
sults.
18
Start next Cycle Measurement
Start the next cycle measurement at the same measure-
ment position here.
19
Ambient Noise Measure / Load / Save
Measure here the actual ambient noise during an adjust-
able measurement time. You may save this record and re-
load the data set for any later speech intelligibility measure-
ment.