In-Car Communication

Since conversational partners in a vehicle do not face each other directly, there is a relatively high attenuation of the speech signal and the signal-to-noise ratio at the listener’s ears is additionally decreased by driving noise. The approach of an in-car communication (ICC) system to resolve this problem is to record the talker’s speech by means of microphones and play it back over loudspeakers which are located close to the listening passengers. Because the listener always perceives a mixture of direct sound and the loudspeaker signal, the system has to be designed to operate with only a small delay of less than 15 ms. Also, such a system operates in a closed electroacoustic loop and thus, system stability becomes a critical issue.

Currently our research is focused on signal processing methods that are required for such kind of systems:

  • beamforming,
  • noise reduction,
  • echo and feedback cancellation, and
  • equalization.

In order to be able to test our algorithms we have several possibilities:

  • While development we have our own real-time simulation of passenger compartments. This is a pure software approach that is included in our real-time toolkit "KiRAT".
  • Furthermore, we have a hardware-based simulation of passenger compartments, meaning that we can test head-units that are equipped with in-car communication systems. The head-unit will "see" 8 Ohm loudspeaker outputs and will get typical VDA microphone signals.
  • For real-time tests in cars we have two research cars available: a sedan and a convertible. Furthermore, we have access to a small bus in order to test new versions of our systems.
  • Since the street, the weather, the traffic, etc. of today is different from yesterdays counterpart we have also an acoustic environmental simulation system that is using a variety of loudspeakers and projectors to create a realistic and reproducible audio and video impressions of a priori recorded setups.


Corresponding Publications

P. Bulling, K. Linhard, A. Wolf, and G. Schmidt: Approximation of the Optimum Stepsize for Acoustic Feedback Cancellation Based on the Detection of Reverberant Signal Periods, Proc. DAGA, Kiel, Germany, open access, 2017

P. Bulling, K. Linhard, A. Wolf, G. Schmidt: Acoustic Feedback Compensation with Reverb-based Stepsize Control for In-car Communication Systems, ITG Speech, October 2016

R. Landgraf, J. Köhler-Kaeß, C. Lüke, O. Niebuhr, G. Schmidt: Can You Hear Me Now? Reducing the Lombard Effect in a Driving Car Using an In-Car Communication System, Proc. Speech Prosody, pp. 479 - 483, 2016

C. Lüke, A. Wolf, M. Brodersen, G. Schmidt: Digitale Simulation der Fahrzeuginnenraumakustik zur Unterstützung der Entwicklung und Evaluierung von Innenraum-Kommunikationssystemen, DAGA 2015, Nürnberg, Germany

T. John, R. Landgraf, C. Lüke, S. Rohde, G. Schmidt, A. Theiß, J. Withopf: Über die Verbesserung der Sprachkommunikation in geräuschbehafteten Umgebungen, in O. Niebuhr (ed.): Formen des Nichtverstehens, Peter Lang, December 2014 (in German)

J. Withopf, S. Rohde, G. Schmidt: Application of Frequency Shifting in In-Car Communication Systems, Proc. ITG Fachtagung Sprachkommunikation 2014, Erlangen, Germany

A. Theiß, G. Schmidt, J. Withopf, C. Lüke: Instrumental Evaluation of In-Car Communication Systems, Proc. ITG Fachtagung Sprachkommunikation 2014, Erlangen, Germany

J. Withopf, G. Schmidt: Estimation of Time-variant Acoustic Feedback Paths in In-Car Communication Systems, Proc. International Workshop on Acoustic Signal Enhancement IWAENC 2014, Antibes, France

A. Theiß, G. Schmidt: Investigation of Self-Masking Effects for the Evaluation of In-Car Communication Systems, Proc. International Workshop on Acoustic Signal Enhancement IWAENC 2014, Antibes, France

C. Lüke, G. Schmidt, A. Theiß, J. Withopf: In-Car Communication, in G. Schmidt, H. Abut, K. Takeda, J. Hansen (eds.), Smart Mobile In-Vehicle Systems, Springer, January 2014

G. Schmidt, A. Theiß, J. Withopf, A. Wolf: Evaluation of In-Car Communication Systems, in J. Hansen, P. Boyraz, K. Takeda, H. Abut (eds.), Digital Signal Processing for In-Vehicle Systems and Safety, Springer, January 2012

J. Withopf, G. Schmidt: Suppression of Instationary Distortions in Automotive Environments, ITG 2012, Braunschweig, Germany, 2012

J. Withopf, L. Jassoume, G. Schmidt, A. Theiß: A Modified Overlap-Add Filter Bank With Reduced Delay, DAGA 2012, Darmstadt, Germany, 2012

C. Lüke, J. Bajorat, G. Schmidt, Real-Time Implementation of an Adaptive Beamformer-Postfilter System, DAGA 2012, Darmstadt, Germany, 2012

J. Withopf, C. Lüke, H. Özer, G. Schmidt, A. Theiß: Signal Processing for In-Car Communication Systems, DSP Workshop for In-Vehicle Systems 2011, Kiel, Germany, 2011

Involved Researchers


Gimm, Marco
PhD student
Signal processing for ICC systems


Namenas, Anton
PhD student
Evaluation of ICC systems


Bulling, Philipp
PhD student (external)
Signal processing for ICC systems


Schmidt, Gerhard
Prof. Dr.-Ing.
Signal processing aspects of the project


Prof. Dr.-Ing. Gerhard Schmidt


Christian-Albrechts-Universität zu Kiel
Faculty of Engineering
Institute for Electrical Engineering and Information Engineering
Digital Signal Processing and System Theory

Kaiserstr. 2
24143 Kiel, Germany

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