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All hardware components required for a test system that checks the quality of the audio system in cars are ac-tually already available in modern cars: DSP, converters, sensors, transducers and connecting links. However, they are not designed as test system components but may be used as such. Smart amplifiers and loudspeaker control technologies are of special interest for this approach. They provide powerful means to improve transducer properties like robustness, linearity, and bandwidth. By definition, they identify loudspeaker parameters and states. Such valuable information can be exploited for test and measure-ment tasks such as design qualification, end-of-line testing, quality assurance, long-term monitoring and ensur-ing safety relevant features (e.g. pedestrian warning systems). This paper investigates benefits and challenges of this approach.
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The sound field excited by high fidelity (hi-fi) audio systems depends on the loudspeaker drivers, their positioning, their enclosures and the listening room. In the case of in-car sound systems, the listening room is the car cabin and its influence is much more pronounced than in typical living-room scenarios. Thus, the user experience results from a complex auditory scene. In certain situations, it is desirable to simulate the resulting auditory scene by means different than the actual audio system, e. g. by using binaural synthesis. In this study, a state-of-the-art binaural synthesis system for living-room scenarios was evaluated with respect to simulate a premium automotive audio system. To this end, listening tests were designed that can identify potential perceptual differences between the original audio system and its simulation. The evaluated aspects include temporal, spectral and spatial attributes. The results show that a convincing simulation of in-car sound systems through binaural headphone reproduction appears to be possible with regard to the evaluated aspects.
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This paper discusses correlations between microphone specifications defined in laboratory conditions and the perceived user experience in automotive applications such as in-car voice communication and array beamforming. Experimental recordings are obtained at various driving conditions using three common types of automotive microphones mounted in three vehicle models (Sedan, SUV and Electric). Speech intelligibility index (SII) and subjective listening based on actual in-car recordings are used to evaluate the communication quality of microphones with different specifications including frequency responses, signal-to-noise-ratios (SNR) and acoustic overload points (AOP). It is shown that, when influences of automotive application environments are considered, microphones with advanced SNR and AOP specifications do not always correlate to higher user experience such as better SII. To study effects of microphone element sensitivity and phase mismatches on beamforming performance, a simulation model is developed. It is found that the tolerance of microphone element-to-element mismatches highly depends on the chosen array processing algorithm. Results in this study could help users and designers choose proper microphone elements for automotive applications.
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Active Noise Cancellation (ANC) and Engine Sound Enhancement (ESE) nowadays are proven standard technologies for low frequency engine noise reduction and sound quality enhancement for conventional as well as modern electric and hybrid electric powertrains. They make use of audio system components to generate the required acoustical output to the vehicle interior. As these technologies define the acoustical character and attributes of the vehicle and its powertrain, their application and the resulting sound must not depend on the actual vehicle audio system level. Therefore, integration of these technologies within the vehicle head-unit, which is typically independent of the actual audio level, is a preferred solution to reduce overall system development and integration complexity. This integration strategy has been strongly supported by the inclusion of freely programmable, open DSP cores within a radio-audio one-chip as e.g. the NXP Dirana3. Currently the next generation of such radio-audio one-chip becomes available. They show significant changes on their open DSP cores which are used for ANC and ESE processing, including newer generation of DSP cores and significant changes on the memory availability and layout. This paper analyses and discusses the impact of the new generation of tuner System-on-Chips (SoCs) on the actual ANC and ESE performance in production vehicles, based on existing software implementations and with a strong focus on the additional system capabilities that will become available for NVH noise management engineers in terms of system flexibility and sound options.
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"Engine Harmonic Cancellation (EHC) is a specific type of Active Noise Cancellation. First introduced in production cars almost three decades ago, the application of EHC is now fairly common. Yet, the criteria for evaluating this technology may not be universally known. After a brief explanation of the technology, its applications and benefits, this paper covers 11 key criteria, which should be considered when evaluating competing systems."
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"Current automotive audio systems are in general distributed systems, both in terms of hardware and functionality. An automotive audio system may contain several DSPs, microprocessors and general purpose multi-core CPUs, with increasingly complex functionality split between processing cores. There are many situations where audio signals need to be passed back and forth between cores, such as for mixing or acoustic echo cancellation, and timing, synchronization, data formats and other discrepancies between components have to be managed, which adds significant complexity and makes the whole system more fragile and inextensible. Some reasons for this division of tasks are historical; in the past, specialized DSPs for audio equalization, filtering, etc. were required to offload the main application processors, and functions such as audio chimes have to boot-up quickly and meet more stringent safety requirements than entertainment signals. Nowadays, general purpose multi-core CPUs (referred to here as GP CPUs), such as ARM or Intel/AMD processors, have advanced considerably and many automotive SoCs feature GP CPUs that run at 2 GHz or more, but the DSP typically remains below 1 GHz. Consolidating audio processing functionality on a single GP CPU with QNX Acoustics Management Platform (AMP) reduces system cost and complexity, improves reliability, accelerates time to market, provides standards-compliance, and brings capabilities and performance to new levels."
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"Constant introduction of new technologies and features in combination with increasingly advanced automotive sound system designs yield challenges for the automotive sound tuning process. Virtual tuning processes are a hot topic in the industry. The main objective is to be less dependent on car availability and allow for early prototyping. In this paper, we present a mixed in-situ/virtual approach that can easily be extended to a full virtual process. The mixed approach presented is implemented today and clearly shows the benefits inherent to a virtual tuning workflow. The match between the presented approach and in-situ validation measurements is investigated and indicates the validity and usability of the presented approach."
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In 2019, Virtual Reality (VR) clearly has found its way into a variety of applications. Leaving behind the gaming and entertainment playground, a significant number of different industries are in the process of adopting Virtual, Mixed and Augmented Reality for integration into their daily workflow. In addition, computational power nowadays allows for highly sophisticated numerical calculations. Multi-physics processes like plastics manufacturing and complex products like a car audio system can be fully modelled and computed within reasonable efforts and time frame. This report is about recent work on a fully-virtual product development workflow for car audio application. A numerical framework was built, featuring all aspects of an automotive audio system. A Virtual Reality system was used to visualize but also to auralize the computationally generated acoustic data, where the Auralization was based on head-tracked dynamic binaural audio reproduction. Interactively controllable features were implemented to enhance the level of immersion. The underlying simulation foundation was evaluated against real measurements during several validation studies. Informal subjective experience tests were conducted, showing feasibly short adaption time of individual subjects to the VR environment and resulting in good overall acceptance by the probands.
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"For system designs in which an automotive audio amplifier DSP architecture doesn’t account for a specific loudspeaker protection algorithm, digital crossover filters placed after the limiter block in the signal flow allow to mitigate the risk of a potential transducer failure due to loudspeakers operating outside of their designated bandwidth at high excursions. Considering a real-world automotive audio system use case with given filtering resources and defined DSP flexibility, this paper discusses various choices for crossover parameters selection and distribution in the system in relation to the limiter block (before and/or after). The impact on loudspeaker bandwidth and crossover behavior is evaluated for several filter-design parameter changes, at varying reproduction level: such analysis considers subwoofer, woofer and midrange loudspeaker cases, eventually leading to a best-compromise design approach."
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"Common loudspeaker cones have axisymmetric geometry and are made of isotropic cone materials, such as paper. This leads to dominant radial cone breakup modes with ring-shaped vibration patterns that create peaks and dips in the frequency response. By adding local masses on the cone in a circle segment configuration, the isotropy is broken due to non-axisymmetric inertial forces. Consequently, the patterns of the breakup modes are changed from ring shaped zones into irregular areas with in-phase and out-of-phase contributions to the sound pressure that cancel each other partially. This leads to a smoothing of the SPL response."
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