Hands-free car kits—A performance discussion of ‘‘state-of-the-art’’ solutions

Abstract

The increasing demand for hands-free solutions in vehicles partly results from safety reasons. In several countries, the use of handsets is already prohibited for drivers. From the technical point of view, not only the ‘‘hands-free problem’’—acoustical stability and echo—has to be solved. The environmental conditions, i.e., noise level and position of microphone and loudspeaker, are extremly critical. Technical implementations include various signal processing methods such as echo cancellers, noise reduction algorithms, and level switching devices. Typically they work in conjunction with codecs (GSM or others). Consequently, speech transmission quality is influenced in various ways. Comparative measurements carried out with eight different hands-free car kits are discussed in this presentation. The test setup guarantees reproducible conditions using the auditory part of a driving simulator, artificial head technology, and a codec simulator. The determination of important objective parameters was carried out with adapted test signals, while real speech samples were used for subjective evaluation. Measurement setup and relevant parameters concerning speech transmission quality are briefly discussed. A number of listening examples demonstrate differences between various implementations.