24 Bedrock SMxx operating manual © Bedrock Audio BV, 2019
25
• A novel test signal is used, which repeats 7 different patterns (segments) in a circular
fashion.
• Each pattern roughly follows the approach of STIPA: each octave band is simultane-
ously modulated with 2 modulation frequencies.
• Each pattern takes approx. 9 seconds to complete. The whole measurement is com-
pleted in 65 seconds.
• The patterns are set up in such a way that all modulation frequencies (out of the set
of 14) have been used in each octave band once the full 65 second cycle is completed.
Hence, all 14 modulation frequencies are tested in all 7 octave bands.
• The first phase of a new measurement is a synchronization phase, during which the
analysis algorithm determines when to expect transitions between patterns.
The Full STI test signal is included on the flashdrive bundled with the SMxx, and will be
available on the Bedrock BTB65 Talkbox starting May 2017. Note that the Full STI signal
is copyrighted material; all audio files of the signal released by Embedded Acoustics are
watermarked. Use of the signal other than directly with the SMxx requires a license from
Embedded Acoustics.
The measurements themselves are no more difficult or complex to carry out than STIPA
measurements. The procedure is largely the same; only the duration is longer and the re-
sults are more univerally representative of true speech intelligibility.
Full STI measurement result (left) and MTF details (right)
The Full STI module has the same overall design as the STIPA pro module, including
the option to computationally add noise. The main difference is the second screen, which
visually represents the Modulation Frequency Transfer (MTF) matrix as it gradually fills
up during the measurement. The user has the option to stop the measurement before the
full cycle has completed, shortening the duration of the measurement. This makes sense
if the STI remains stable across multiple phases of the signal. The result of a prematurely
To Next Page
Loading...