Download Signal Decorrelation using Perceptually Informed Allpass Filters When a monophonic source signal is projected from two or more loudspeakers, listeners typically perceive a single, phantom source, positioned according to the relative signal amplitudes and speaker locations. While this property is the basis of modern panning algorithms, it is often desirable to control the perceived spatial extent of the phantom source, or to project multiple, separately perceived copies of the signal. So that the human auditory system does not process the loudspeaker outputs as a single coherent source, these effects are commonly achieved by generating a set of mutually decorrelated (e.g., statistically independent) versions of the source signal, which are then panned to make an extended source or multiple, independent source copies. In this paper, we introduce an approach to decorrelation using randomly generated allpass filters, and introduce numerical methods for evaluating the perceptual effectiveness of decorrelation algorithms. By using allpass filters, the signal magnitude is preserved, and the decorrelated copies and original signal will be perceptually very similar. By randomly selecting the magnitude and frequency of the poles of each allpass biquad section in the decorrelating filter, multiple decorrelating filters may be generated that maintain a degree of statistical independence. We present results comparing our approach (including methods for choosing the number of biquad sections and designing the statistics of the pole locations) to several established decorrelation methods discussed in the literature.
Download Assessing Applause Density Perception Using Synthesized Layered Applause Signals Applause signals are the sound of many persons gathered in one place clapping their hands and are a prominent part of live music recordings. Usually, applause signals are recorded together or alongside with the live performance and serve to evoke the feeling of participation in a real event within the playback recipient. Applause signals can be very different in character, depending on the audience size, location, event type, and many other factors. To characterize different types of applause signals, the attribute of ‘density’ appears to be suitable. This paper reports first investigations whether density is an adequate perceptual attribute to describe different types of applause. We describe the design of a listening test assessing density and the synthesis of suitable, strictly controlled stimuli for the test. Finally, we provide results, both on strictly controlled and on naturally recorded stimuli, that confirm the suitability of the attribute density to describe important aspects of the perception of different applause signal characteristics.
Download Complexity Scaling of Audio Algorithms: Parametrizing the MPEG Advanced Audio Coding Rate-Distortion Loop Implementations of audio algorithms on embedded devices are required to consume minimal memory and processing power. Such applications can usually tolerate numerical imprecisions (distortion) as long as the resulting perceived quality is not degraded. By taking advantage of this error-tolerant nature the algorithmic complexity can be reduced greatly. In the context of real-time audio coding, these algorithms can benefit from parametrization to adapt rate-distortion-complexity (R-D-C) trade-offs. We propose a modification to the rate-distortion loop in the quantization and coding stage of a fixed-point implementation of the Advanced Audio Coding (AAC) encoder to include complexity scaling. This parametrization could allow the control of algorithmic complexity through instantaneous workload measurements using the target processor’s task scheduler to better assign processing resources. Results show that this framework can be tuned to reduce a significant amount of the additional workload caused by the ratedistortion loop while remaining perceptually equivalent to the fullcomplexity version. Additionally, the modification allows a graceful degradation when transparency cannot be met due to limited computational capabilities.