Journal of the Audio Engineering Society

2007 November - Volume 55 Number 11

Papers


[Feature] The face of broadcasting is changing in the age of the internet. How are broadcasters tackling the challenges of new technology now that audio can be delivered to the consumer in so many different ways, including by satellite, wired or wireless network, or terrestrial broadcast? Are audio on demand and broadcasting the same things?

A special type of magnitude complementary IIR filter pair with variable transition bandwidths and impulse response lengths was used to examine the effects of these two characteristics on the subjective perception of reproduced sound. Two types of listening tests were performed. In the first the sum of crossover outputs was compared to the original signal. In the second the IIR filter pairs were compared among themselves, as well as with linear-phase magnitude complementary FIR filter pairs as a reference. The results of the tests show that the overall differences are not significant. It was found that the filters considered are suitable for loudspeaker crossover applications.

The PEM-AFROW algorithm has been developed to model a room impulse response under closed-loop conditions, such as in microphone-amplifier-loudspeaker systems, and is particularly suited for a speech signal input. If a controller is inserted in the loop that uses this model to remove the loudspeaker signal component from the microphone signal, an efficient feedback cancellation can be performed. Crucial implementation-oriented issues that have not been studied so far are addressed. In particular, adaptation control mechanisms are proposed for feedback cancellation based on PEM-AFROW, and efficient subband and frequencydomain implementations are provided for this algorithm.

Beat Deviation for Tempo Estimation Algorithms

Authors: Rossiter, David; Tsang, Raymond; So, Richard H. Y.

The series of beats in an arbitrary piece of music typically do not have a precisely consistent interval of time between them. A study was carried out to analyze beat deviation. Five musicians tapped beat sequences for 50 recordings taken from 16 different categories of music. A power curve was proposed to represent the beat deviation. The curve is shown to capture the majority (96.9%) of the beat data entered by the subjects in this study, with a minimum chance of nonbeat events being accepted as valid beats. The proposed power curve equation is compared to others in published research. Measures of BPM deviation used in previous studies are also considered.

[Engineering Report] An optimal source distribution (OSD) has recently been proposed that overcomes a number of the problems that are often associated with binaural synthesis over loudspeakers. Such problems include a loss of dynamic range and a high sensitivity to small errors of control performance. These problems are overcome by means of a conceptual monopole transducer pair whose span varies as a function of frequency. The results are reported of objective and subjective experiments used to evaluate a system comprised of discrete loudspeaker elements whose design is based on the principle of the OSD.

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