STI/PA Analyzer

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Speech intelligibility measurements

STIPA and full STI (fast method)

Built-in STI/STIPA signal generator

Calculates average STI from multiple measurements

Data stored in human-readable JSON files for later review

Designed to meet or exceed the requirements of IEC standard 60268-16, Edition 5.0 (2020-09)

Input: 1 channel at a time, selected from any available input, output, or virtual output channels
Test Type: STIPA, STI Fast
STIPA Measurement Durations (seconds): 15, 18, 21, 25
STI Fast Measurement Durations (seconds): 8, 12, 15, 18
Auditory Masking Correction: Enable/Disable
Speech Reception Threshold Correction: Enable/Disable
Expected Test Signal Modulation Depth: 0.55

Added Noise

Built-in Test Signal Generator

Enable/Disable
Signal Type: STIPA or related STI signal with alternate modulation frequencies per octave band
Presend (seconds): User-definable value greater than or equal to zero
Level: specified in dBFS where 0 dBFS is the maximum (full scale) output amplitude
Output Channel: Selected from any available output or virtual output channels
Modulation Depth: 0.55

Display

Display Type: Octave Band Levels, MTF (Modulation Transfer Function Matrix), TI (Transmission Index Matrix)
Supported Octave Bands: 125, 250, 500, 1000, 2000, 4000, 8000
Autoscale Off, Auto
dB Level Scale (dB/Div) 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.8, 0.9, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 8.0, 9.0, 10.0, 12.0, 15.0, 16.0, 18.0, 20.0, 24.0, 25.0, 27.0, 30.0

Data Export

Test data is automatically saved each time a measurement reaches the user-selected duration.
Data File Format: JSON

Data Import

Additional Specifications

Modulation depth

STIPA and STI (Fast) test signals employ a modulation depth of 0.55. A perfect STI of 1.0 requires that the received signal also exhibit a modulation depth of 0.55, which would result in a modulation transfer ratio (m-value) of 1.0.
EC 60268 requires that the absolute value of any error in m-value determination not exceed 0.05 and that all m-value errors not yield an error in the overall STI value greater than 0.01.
In our testing of STIPA measurements made with SignalScope, using standard verification signals available from www.stipa.info, we observed differences between measured m-values and expected m-values of no greater than 0.011 across all frequency bands and modulation frequencies.
Our tests were performed by analyzing the digital signals directly--no analog circuitry was included in the signal path. The STIPA measurement ran with the standard's recommended averaging time of 18 seconds.

Crosstalk between octave-band filters

Poor design of the octave-band filters can lead to crosstalk which effectively increases the noise level in adjacent frequency bands, causing the m-values to be underestimated. A STIPA measurement device can be tested for this using the standard verification signals avilable from www.stipa.info.
When testing filter performance using standard verification signals, the m-value in each octave band can be observed with a high-amplitude signal present in an adjacent octave band. IEC 60268 requires that the m-value in the observed band be at least 0.5 (+/-0.05).
In our testing with SignalScope, the minimum m-value in any observed band with any modulation frequency across all test cases was 0.607.
Our tests were performed by analyzing the digital signals directly--no analog circuitry was included in the signal path. The STIPA measurement ran with the standard's recommended averaging time of 18 seconds.

Supported octave frequency bands and modulation frequencies

STIPA

Octave Band, Hz	125	250	500	1k	2k	4k	8k
Mod Freq (Fm)	1.60 & 8.00	1.00 & 5.00	0.63 & 3.15	2.00 & 10.0	1.25 & 6.25	0.80 & 4.00	2.50 & 12.5

Full STI (Fast)

Octave Band, Hz	125	250	500	1k	2k	4k	8k
Fm, Meas. Part 1	1.60 & 8.00	1.00 & 5.00	0.63 & 3.15	2.00 & 10.0	1.25 & 6.25	0.80 & 4.00	2.50 & 12.5
Fm, Meas. Part 2	1.00 & 5.00	0.63 & 3.15	2.00 & 10.0	1.25 & 6.25	0.80 & 4.00	2.50 & 12.5	1.60 & 8.00
Fm, Meas. Part 3	0.63 & 3.15	2.00 & 10.0	1.25 & 6.25	0.80 & 4.00	2.50 & 12.5	1.60 & 8.00	1.00 & 5.00
Fm, Meas. Part 4	2.00 & 10.0	1.25 & 6.25	0.80 & 4.00	2.50 & 12.5	1.60 & 8.00	1.00 & 5.00	0.63 & 3.15
Fm, Meas. Part 5	1.25 & 6.25	0.80 & 4.00	2.50 & 12.5	1.60 & 8.00	1.00 & 5.00	0.63 & 3.15	2.00 & 10.0
Fm, Meas. Part 6	0.80 & 4.00	2.50 & 12.5	1.60 & 8.00	1.00 & 5.00	0.63 & 3.15	2.00 & 10.0	1.25 & 6.25
Fm, Meas. Part 7	2.50 & 12.5	1.60 & 8.00	1.00 & 5.00	0.63 & 3.15	2.00 & 10.0	1.25 & 6.25	0.80 & 4.00

* Specifications subject to change

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