10. March 2021

Speech Intelligibility ed5 Standard Adapted

Edition 5 (ed5) of the IEC 60268-16 speech intelligibility measurement standard became effective at the end of September 2020. The latest firmware 4.50 of the XL2 now supports measurements from Ed2 through to ed5. Since the excitation signals for ed5 have also changed slightly, they are available for free download to all STIPA users at my.nti-audio.com.


Adaptation of the excitation signals

In September 2020, the IEC 60268-16 ed5 standard on the measurement of speech intelligibility was launched. The most significant change in ed5 is the spectral weighting of the excitation signals being slightly increased overall and lowered in the lower bands in order to better match the spectrum to that of a human speaker according to the latest findings.

Comparison of STIPA Spectrum for ed4 and ed5

This means that the new ed5 test signal contains less low-frequency energy and can also be radiated by systems that are less powerful than the NTi Audio TalkBox. The matched signals are available for free download to all STIPA users at my.nti-audio.com and can be loaded directly into the NTi Audio TalkBox. New TalkBoxes and Minirators will be shipped from the factory with the new test signal according to ed5.


Will there be problems if I mix ed4 and ed5?

The XL2 can be freely switched to measurement editions from ed2 to ed5 after each STIPA measurement. There are no differences between ed4 and ed5 in the analysis core and therefore no measurement errors will be introduced.

However, it may happen that you need to measure according to ed4 but only have a TalkBox with ed5 signals available, or conversely you want to measure according to ed5 but only the ed4 signals are available. Although the levels differ by up to 6 dB, the wrong excitation signal affects the measurement results by less than 0.01 STI on average, since the weighting of the modulation values to the low frequencies is massively attenuated, and thus hardly influences the measurement result. The standard deviation of the measurement error is 0.015 STI, while the maximum error is 0.03 STI. In only 2% of the cases does the measurement uncertainty exceed the maximum tolerated level of 0.03 STI.


An adapted STI application note can be downloaded here:

The new firmware V4.50 for XL2 with selection of the updated standard IEC 60268-16:2020 (ed5) can be found here:

The STI Reporter software has also been adapted accordingly: