Abstract
Communicating inside a car can be difficult because there is usually a high level of background noise and also the talking and the listening passengers do not necessarily face each other as they would do in a natural conversation. In-car communication (ICC) systems are a solution to this problem. They record the talkers’ speech signal by means of microphones and reproduce it over loudspeakers that are located close to the listening passengers. However, such systems operate in a closed electroacoustic loop which significantly limits the gain that can be introduced by the system. In order to improve this gain margin and to achieve additional signal enhancement, several signal processing techniques are applied in ICC systems. Special care has to be taken about the signal delay: If it is too large, the reverberation inside the car is increased considerably and the speech reproduced over the loudspeakers might be perceived as an echo by the speaking passengers. In this chapter, an overview of the signal processing components of an ICC system is given. The necessary signal processing steps are explained and approaches to implement them are shown, especially with a focus on low processing delays.
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Notes
- 1.
If the delay and the computational load of the analysis and synthesis filter banks are neglected.
- 2.
The subbands can also be seen as time-aligned spectra if all filter bank channels are considered at a certain time instance.
- 3.
From now on, the tilde is used to annotate these “user-friendly” variables.
- 4.
The user-friendly variables are obtained by the conversion similar to (7.12).
- 5.
This is likely to happen if microphones are integrated into the seat belts.
- 6.
The concept of mel-filtering is, e.g., commonly used in the feature extraction for speaker and speech recognition, see [24].
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Lüke, C., Schmidt, G., Theiß, A., Withopf, J. (2014). In-Car Communication. In: Schmidt, G., Abut, H., Takeda, K., Hansen, J. (eds) Smart Mobile In-Vehicle Systems. Springer, New York, NY. https://doi.org/10.1007/978-1-4614-9120-0_7
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