INSTRUMENTATION • ELECTRONICS
A 3D model of KEMAR
Te STI is a measurement and calculation method that includes a number of parameters. Using the STI along with valid data, one can calculate the speech intelligibility that will be achieved under the given circumstances. Te STI finding is presented on a scale and is used in various standardised norms as an expression of how understandable a speech is received. A higher value means a better understanding – less effort for the recipient – which can contribute to a better user experience. However, a key factor in usefully applying this index is accurate, valid data that matches realistic communication in a cabin. Te best way to acquire such data is through the use of a HATS such as GRAS KEMAR, which is specifically designed to acquire the data just as an actual human occupying that space would.
HOW GRAS KEMAR WORKS KEMAR meets the IEC 60318-7 human head and ear simulator standard that describes a realistic head and body geometry. With a HATS like KEMAR occupying the measurement positions, a realistic measurement environment is created because it fills the space in the
cabin that otherwise consists of driver and passenger. Tis creates realistic sound reflections and dampening just as and when a person is sitting in a car. Using two or more KEMAR in the same cabin, you can simulate how a talker and a receiver interact. KEMAR’s binaural capability –
microphone in both the left and right ear – provides a benefit beyond the basic acquired STI data. For example, the ear closest to the window will typically perceive more wind noise and thus reduce the general speech intelligibility. Being able to separate the right and left channels in your research can be useful for pin- pointing where improvements can be made. If there is a 3D geometry of the HATS (as there is with KEMAR), that performance can be simulated in FEM/ BEM models, already in the design phase.
A FULL TEST SYSTEM Further from the STI, specifically concerned with human communication with infotainment systems, are the Perceptual Objective Listening Quality Assessment (POLQA) and Perceptual Evaluation of Speech Quality (PESQ). Tese tests use the cabin environment
and a speaker and receiver to compare an audio output (at the phone line’s ‘listener’ end) to the original voice file (played on the ‘talker’ side) to create a fully unbiased and objective indicator of the actual audio being heard. Tis is more accurate than the other methods of audio quality measurement which often rely on audio quality predictions based on network performance.
Combining an analyser and software that support POLQA and PESQ, such as Audio Precision APx500 with KEMAR – which can also be used for measuring the transmission performances of car hands-free terminals – can form a full test system that provides the required data to improve speech intelligibility and overall human-vehicle communication earlier in the design process. Tese tools together can create a safer, less stressful and more pleasing environment for vehicle occupants.
Brian Johansen is an Acoustic Engineer at GRAS Sound & Vibration.
www.grasacoustics.com
www.engineerlive.com 21
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