1:00, AUDIO-L1.1
A MODIFIED OVERALL ON-LINE MODELING ALGORITHM FOR THE FEEDFORWARD MULTIPLE-POINT ANC SYSTEM
T. YEUNG, S. YAU
This paper proposes a modified overall on-line modeling algorithm for application in feedforward multiple-point active noise control (ANC) system, in which acoustic paths decoupling can be improved. First, the structure of the ANC system adopting the proposed method is discussed. Second, the update equations of the system modules employing the LMS algorithm are derived. Next, the off-line initialization procedures of the system modules together with the update equations are described. Computer simulations illustrate the performance of the feedforward multiple-point ANC system adopting the proposed method. Simulation results show that the system can achieve superb low-frequency noise reduction and the reconvergence of the system error is guaranteed even when changes are encountered into the primary and secondary paths.

1:20, AUDIO-L1.2
ACTIVE NOISE CONTROL USING ROBUST FEEDBACK TECHNIQUES
M. O'BRIEN, P. PRATT
With the resurgence of active noise control in the past two decades, the design and implementation of optimal noise cancellers have been a topic of considerable research. Recently, much of the investigation has been focused on fixed controllers that rely on the robustness of closed loop systems to deal with poorly parameterized or changing plants. Many acoustic systems employ internal model controller structures designed via H-inf techniques to attain optimality. Absent from the literature, however, is a qualitative study of classical robust controllers applied to the active noise problem. This paper looks at the practical issues and possible pitfalls of applying H-inf optimal feedback controllers to one-dimensional acoustic ducts. In particular, it is observed that the relatively high degree of non-minimum-phase zeros, typical of acoustic plants, limits the ultimate performance of the optimal H-inf solution.

1:40, AUDIO-L1.3
EFFECTS OF SECONDARY PATH MODELING ERRORS ON THE MODIFIED FX-LMS ALGORITHM FOR ACTIVE NOISE CONTROL
P. LOPES, M. PIEDADE
The Modified FX-LMS (MFX-LMS) algorithm has been the subject of some research. It effectively removes the delay from the adaptation mechanism allowing faster convergence rates than the FX-LMS. It also allows the use of more sophisticated algorithms such as the RLS or the Kalman. Although this is true for perfect secondary path modeling, there is no extensive study of the influence of secondary path modeling errors in this algorithm. This paper tries to do just that. It shows that it's maximum allowed step-size is in fact almost independent of the delay in the secondary path, even in the presence of modeling errors. It also shows that for very large delays the algorithm is stable for phase errors of +-60º and for an estimated amplitude of more than half of the correct one.

2:00, AUDIO-L1.4
FREQUENCY DOMAIN ACTIVE NOISE CONTROL SYSTEM USING OPTIMAL STEP-SIZE PARAMETERS
Y. KAJIKAWA, Y. NOMURA
In this paper, we propose a frequency domain active noise control system using optimal step-size parameters at each frequency. The proposed ANC system can converge faster than the conventional ANC system using the Filtered-x LMS algorithm with the optimal step-size parameter. Moreover, the proposed system can converge by setting the step-size parameters at unstable frequencies to 0 in the case where the phase error of the secondary path model does not satisfy the stable condition, whereas the conventional ANC system cannot converge in this case. In this paper, the theoretical equation of the optimal step-size parameters is derived by using available information during system operation. Next, we present the structure of the ANC system using the optimal step-size parameters obtained from the theoretical equation. Moreover, a control technique determining unstable frequencies is introduced. Finally, simulation results demonstrate the efficiency of the proposed ANC system.

2:20, AUDIO-L1.5
RECURSIVE LEAST-SQUARES ALGORITHMS WITH GOOD NUMERICAL STABILITY FOR MULTICHANNEL ACTIVE NOISE CONTROL
F. YU, M. BOUCHARD
Some recursive least-squares algorithms for multichannel active noise control have recently been introduced, including computationally efficient (i.e. “fast”) versions. However, these previously published algorithms suffer from numerical instability due to finite precision computations. In this paper, numerically robust recursive least-squares algorithms for multichannel active noise control systems are introduced, using QR decompositions and lattice structures. It is shown through simulations of broadband multichannel active noise control that the recursive least-squares algorithms introduced in this paper are indeed more numerically robust than the previously published algorithms, while keeping the same convergence behavior, and therefore they are more suitable for practical implementations.

2:40, AUDIO-L1.6
SUBJECTIVE EVALUATION OF ACTIVELY CONTROLLED INTERIOR CAR NOISE
M. DE-DIEGO, A. GONZALEZ, G. PINYERO, M. FERRER, J. GARCIA-BONITO
This work is a preliminary study which focused on subjective improvements of vehicle interior noise by using active noise control techniques. A local active noise control system has been mounted inside a room in order to reduce synthesized and real engine noise in the area around the headrest of a typical car seat. Recordings before and after cancellation have been made using a Head Acoustics mannequin positioned in the seat with two calibrated microphones at the ear-canals. Two methods were used to evaluate the comfort improvements achieved by active noise control. First, a prediction model of comfort based on four psychoacoustic descriptors (loudness, roughness, sharpness and tonality) was applied. Secondly, the subjective evaluation of controlled signals was carried out by means of a jury test. The reduction of noise levels does not necessarily reduce the annoyance of car engine noise, that depends on spectral characteristics of noise.