Journal of the Audio Engineering Society

2008 April - Volume 56 Number 4


A smart virtual reality presentation system, using only two loudspeakers, allows for a dynamically selected sweet spot that can be positioned at the arbitrary location of the listener. An efficient asymmetric crosstalk cancellation creates the needed filters to reposition the sweet spot; and a specialized remote control held by the listener allows the system to determine the angle and distance to the listener. Informal listening tests showed that the proposed approach can enhance the surround sound effect for television listening. Compared to conventional playback, listeners preferred this system at every location.

Efficient Audio Equalization Using Multirate Processing

Authors: Väänänen, Riitta; Hiipakka, Jarmo

The excessive computational burden of some specialized equalization requirements can be reduced by using multirate processing. Quadrature mirror filters split the audio signal into narrow bands that can be downsampled and then filtered with modest processing loads. The composite bands are then upsampled and reconstructed into a full-band signal. The main advantage of this approach is design flexibility since the filters in each band can be implemented independently of each other.

When reproducing a two-dimensional higher order Ambisonic soundfield with a uniformly distributed loudspeaker array, there is a tradeoff that depends on the radius of the reproduction area, the order, and the wave number. For classical first-order Ambisonics, perfect reconstruction is possible in a tiny sweet spot, and filtering can be used with a larger number of loudspeakers. However, for a larger sweet spot, higher order Ambisonics must be used and the number of loudspeakers must be matched to the order because filter compensation is not possible. The number of loudspeakers is a tradeoff between spectral impairment at high frequencies and reproduction errors at low frequencies.

Using various signal processing technologies, a microphone system has been developed to enhance hands-free communications in automobiles. The steered microphone array functions as a highly directive beamforming spatial filter, thereby emphasizing the location of the selected talker. Experimental results demonstrate that a steered response power-phase transform algorithm is robust in reverberant and noisy environments.

Orchestrating Automotive Audio

Authors: Rumsey, Francis

[Feature] The automotive environment is now one of the most important research areas in audio engineering, but it is also one of the most challenging. Not only is the acoustical environment quite unusual and the space rather small in comparison to most rooms, but also there are numerous compromises to be made in system design owing to factors such as the off-center listening position, competition for real estate on the dashboard and in other locations within the car, and the limited volume available for loudspeaker enclosures. Some of these issues were discussed in a series of papers and a workshop presented at the AES 123rd Convention held in New York in October 2007. Among them were the topics of improved stereo imaging in automobiles and the design of a listening test system for automotive audio. The workshop dealt with the tricky subject of uneven bass reproduction in automobiles.

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