Authors: Gover, Bradford N.
A spherical microphone array has been used to perform directional measurements of airborne sound transmission between rooms. With a source and an array on opposite sides of a wall, omnidirectional impulse responses were measured to each of the array microphones. Beamforming resulted in a set of directional impulse responses, which were analyzed to find the distribution of arriving sound energy at the array position during various time ranges. Weak spots in the separating wall are indicated as directions of increased arriving sound energy. The system was able to identify minor defects in a test wall between two reverberation chambers, and also to identify leaks in the wall of an actual meeting room.
Authors: Loutridis, Spyros J.
The application of the continuous wavelet transform, implemented with complex wavelets, to the decomposition of loudspeaker and room impulse responses is discussed. The wavelet transform possesses adaptive time–frequency resolution and is very well suited to the analysis of transient signals. It has the important property that significant signal information is concentrated on certain regions called ridges. Applications include separation of modal components with subsequent damping estimation and low-frequency coloration detection. Wavelets form filter banks and can be designed to have any desirable filter bandwidth. Wavelet filters are used for reverberation-time estimation. It is also suggested that complex wavelets might be used for envelope extraction and calculation of the instantaneous frequency and instantaneous spectral density of a signal.
Authors: Bai, Mingsian R.; Bai, Ganyuan
Reverberators are key elements in three-dimensional spatial audio reproduction. The richness and spaciousness of reproduced sound can be enhanced with reverberators. Infinite impulse response (IIR) filters such as all-pass or comb filters are commonly used in reverberator design. An inadequate choice of the filter parameters in these reverberators often results in audible artifacts such as metallic and ringing sound. To minimize the effort of trial and error in parameter tuning when designing reverberators, an automatic search procedure based on genetic algorithms (GA) is presented. The architecture of the present reverberator consists of a finite impulse response (FIR) early reflection module and an IIR late reverberation module. To facilitate the choice of filter parameters according to the room modes specified by the user, an intelligent user interface is developed on the basis of fuzzy logic. Subjective listening tests were carried out to assess the performance of the proposed reverberators. The results indicate that, when compared to conventional reverberators, the presented reverberator is capable of delivering natural sounding reverberation.
Authors: Wun, Simon; Horner, Andrew
[Engineering Report] Matching musical instrument tones is a classic problem in computer music. Previous work has shown various noniterative methods to be successful. Iterative methods, where the basis spectra are found one by one over several iterations, have received much less attention. Iterative methods are more efficient, with a linear running time. Several iterative methods are evaluated and compared. Matching results for a range of instruments show, surprisingly, that iterative local search can find matches comparable to near-optimal noniterative matches. As an added advantage, iterative local search offers real-time control of the number of wavetables, allowing computation and memory efficiency, and good matching accuracy.
Authors: Staff, AES
[Feature Article] Digital music comes in different formats. However, in this article we concentrate on formats for representing musical notation in a digital form, which primarily means musical scores or parts, although, as will be seen, it can include additional information, even audio in some cases. Since the 1980s such formats have been evolving, and at last count there were over 60 different means of representing such information in a form suitable for use on a computer. The aim here, therefore, is not to attempt to describe all of the formats in existence, but to explain some of the different approaches and summarize the current state of the art. (Some additional links and resources relating to musical notation codes are listed at the end of the article.) Although there are a variety of proprietary formats in use for the exchange of music-notation data, corresponding to key commercial application packages such as Sibelius, Finale, and SCORE, this article concentrates on those publicly available formats that have been aimed at enabling interchange between systems.
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