A key feature of extended target (ET) is that it can produce multiple measurements, thus providing detailed information such as size, orientation. However, due to the measurement number decrease, the ET tends to be a point target (PT) when it becomes far from the sensor, leading to disability of estimating the extensions. In this paper we consider the problem of distributed ETs tracking based on multiple sensors. In such a case the measurements decrease of an ET can be compensated by other sensors, so that the tracking performance can be maintained. In the proposed algorithm the targets are modeled by Poisson multi-Bernoulli (PMB) random finite set (RFS) and the state of each target consists of two parts representing the possibility of being ET and PT, respectively. In the local filtering state, interaction between ET and PT states is considered in the prediction step for target identity change between ET and PT, based on which the local PMB filter is achieved for seamlessly tracking ETs and PTs. In the fusion part a generalized covariance intersection (GCI) based criterion is proposed to fuse the posteriors of each sensor. The performance of proposed algorithm is verified via simulations.

The virtual bass system (VBS) can enhance the bass performance of small or flat loudspeakers by tricking the human brain to perceive the fundamental frequency from its higher harmonics. However, additional harmonics may lead to arithmetic overflow and cause distortion due to clipping, especially during high-level transient components. Past research pay little attention on this problem, and manual control of VBS gain settings is required to prevent overflow. Users need to manually adjust the gain settings for different sound tracks, which can be very troublesome. In this paper, we propose a VBS that can efficiently prevent the overflow problem by automatically controlling the gain settings for additional harmonics. This new approach pre-computes the gain limitation for additional harmonics and can be adopted for real-time audio implementation. Objective measurements are carried out to compare the proposed method with the commonly used limiter method.

Due to the physical size and frequency response constraints of miniaturized and flat panel loudspeakers, low frequency reproduction from these loudspeakers is generally limited and unsatisfactory. The virtual bass system (VBS) enhances the bass performance of such loudspeakers by tricking the human brain to perceive the fundamental frequency from its higher harmonics. Problematically, the additional harmonics from VBS can also introduce perceptual distortion and reduce the audio quality. Therefore, a reliable method to assess the quality of VBS-enhanced signals is necessary in the designing of VBS. Since subjective experiments are often time-consuming and may be inconsistent, it is desirable to develop an objective assessment method for VBS. Earlier studies only utilized some simple objective metrics, which generally do not consider the human auditory model and are unable to accurately predict the perceptual quality of VBS. In this paper, we introduce a perceptual quality-assessment method for VBS based on the model output variables (MOVs) of the ITU Recommendation ITU-R BS.1387. Suitable combinations of MOVs are selected to derive perceptual quality metrics that correlate closely to the subjective quality. A verification experiment is presented to justify the accuracy of the metrics.

Small and flat loudspeakers usually result in poor low-frequency (or bass) responses. Conventional gain equalization does not help significantly and may even result in overdriving and distortion. A psychoacoustic approach has been found to be suitable in tricking the human ear to perceive the fundamental frequency from its higher harmonics. Past research efforts have generally focused on weighting the harmonics based on the loudness matching method, but no work on timbre matching has been carried out so far. In this paper, we propose a new timbre matching technique, which can improve the sound quality of the psychoacoustically enhanced bass. This approach adjusts the amplitude of harmonics to produce similar timbre as the original audio content. Objective and subjective tests are carried out to compare the audio quality of the psychoacoustic bass enhanced signal using the equal-loudness weighting and the timbre matching methods.

The parametric loudspeaker is a novel type of loudspeaker that can project a directional sound beam. It is commonly used in creating personal sound zone and projecting private messages to a targeted audience. However, the parametric loudspeaker possesses a very poor bass (or low-frequency) response due inherently to the nonlinear acoustic principle generating sound from ultrasound in air. A psychoacoustic signal processing method known as “virtual bass” has been successfully implemented in some consumer electronics with miniature or flat loudspeaker unit, aiming to enhance their bass performances. In this paper, we adapt this “virtual bass“ approach for parametric loudspeakers. Unlike conventional loudspeakers, the parametric loudspeaker brings in an added degree of complexity in “virtual bass” enhancement due to its inherent nonlinear acoustic property. Accordingly, a new preprocessing technique is proposed for the parametric loudspeaker to psychoacoustically reproduce the low-frequency components within an octave below its cut-off frequency.

Psychoacoustic bass (low frequency) enhancement approach has received strong interests from consumer electronics manufacturers who demand good bass quality from small or flat panel speakers. Due to physical limitations and cost constraints, good bass performance is lacking from such speakers. A typical solution is based on the psychoacoustic phenomenon known as the “missing fundamental”, whereby human auditory system can perceive the fundamental frequency from its higher harmonics. This psychoacoustic bass enhancement system generally uses nonlinear devices (NLD) or phase vocoders (PV) to generate harmonics that enhance bass virtually. However, both approaches have their strengths and weaknesses. This paper presents a hybrid system, which combines these two approaches, to overcome their drawbacks and achieve good bass performance. The new approach first separates musical signals into transient and steady-state components, and applies NLD and PV on the separated signals. MUSHRA subjective test is used to evaluate the bass effect and audio quality of the proposed hybrid system against the NLD and PV methods.