In this paper we show several digital signal processing techniques that can be used for non-exponentially decaying artificial reverberation. Traditional recursive filter techniques used for simulating the diffuse part of reverberation produce an exponentially decaying reverberation. We show how traditional reverberation algorithms can be modified and combined to create non-exponentially decaying reverberation. The techniques presented here can be used for interesting musical effects and speech enhancement. As an application example, a real-time system using the Motorola DSP56002 digital signal processor is presented.

Download

In this paper a new auditorily motivated analysis method for room impulse responses is presented. The method applies same kind of time and frequency resolution than the human hearing. With the proposed method it is possible to study the decaying sound field of a room in more detail. It is applicable as well in the analysis of artificial reverberation and related audio effects. The method, used with directional microphones, gives us also hints about the diffuseness and the directional characteristics of the sound fields in the time-frequency domain. As a case study two example room impulse responses are analyzed.

Download

This paper presents a new time-variant reverberation algorithm that can be used in reverberation enhancement systems. In these systems, acoustical feedback is always present and time variance can be used to obtain more gain before instability (GBI). The presented time-variant reverberation algorithm is analyzed and results of a practical GBI test are presented. The proposed reverberation algorithm has been used successfully with an electro-acoustically enhanced rehearsal room. This particular application is briefly overviewed and other possible applications are discussed.

Download

A novel way of controlling a simple user interface based on detecting and localizing finger snaps of the user is presented. The analysis method uses binaural signals recorded from the ears of the user. Transient sounds are first detected from a continuous audio stream, followed by cross-correlation based localization and simple band-energy ratio based classification. The azimuth plane around the user is divided into three sectors, each of which corresponds to one of the three “buttons” in the interface. As an example, the interface is applied for controlling the playlist of an MP3 player. The algorithm performance was evaluated using a real-world recording. While the algorithm looks promising, more research is needed before it is ready for commercial applications.

Download

A novel analysis method for binaural room impulse responses (BRIRs) is presented. It is based on the analysis of ear canal signals with continuous wavelet transform (CWT). Then, the crosswavelet transform (XWT) is used for detection of the direct sound and individual reflections from a BRIR. The new method seems to time-localize the reflections quite accurately. In addition, the proposed analysis method enables detailed study of the frequency content of the early reflections. The algorithm is tested with both measured and modeled impulse responses. A comparison with an FFT-based cross-spectrogram is made. The results show that XWT has potential in audio signal analysis.

Download

Virtual acoustics and auralizations have been previously used to study the perceptual properties of concert hall acoustics in a descriptive profiling framework. The results have indicated that the apparent auditory distance to the orchestra might play a crucial role in enhancing the listening experience and the appraisal of hall acoustics. However, it is unknown how the acoustics of the hall influence auditory distance perception in such large spaces. Here, we present one step towards studying auditory distance perception in concert halls with virtual acoustics. The aims of this investigation were to evaluate the feasibility of the auralizations and the system to study perceived distances as well as to obtain first evidence on the effects of hall acoustics and the source materials to distance perception. Auralizations were made from measured spatial impulse responses in two concert halls at 14 and 22 meter distances from the center of a calibrated loudspeaker orchestra on stage. Anechoic source materials included symphonic music and pink noise as well as signals produced by concatenating random segments of anechoic instrument recordings. Forty naive test subjects were blindfolded before entering the listening room, where they verbally reported distances to sound sources in the auralizations. Despite the large variance in distance judgments between the individuals, the reported distances were on average in the same range as the actual distances. The results show significant main effects of halls, distances and signals, but also some unexpected effects associated with the presentation order of the stimuli.

Download

Virtual reality applications require all kinds of methods to create plausible virtual acoustics environments to enhance the user experience. Here, we present an acoustic paintbrush method that modifies the timbre of a simple room acoustics simulation with the timbre of a measured room response while aiming to preserve the spatial aspects of the simulated room. In other words, the method only applies the measured spectral coloration and alters the simulated and temporal distribution of early reflections as little as possible. Three variations of the acoustic paintbrush method are validated with a listening test. The results indicate that the method works reasonably well. The paintbrushed room acoustic simulations were perceived to become closer to the measured room acoustics than the source simulation. However, the limits of the perceived effect varied depending on the input signal and the simulated and recorded responses. This warrants for further perceptual testing.

Download

In virtual acoustics, it is common to simulate the early part of a Room Impulse Response using approaches from geometrical acoustics and the late part using Feedback Delay Networks (FDNs). In order to transition from the early to the late part, it is useful to slowly fade-in the FDN response. We propose two methods to control the fade-in, one based on double decays and the other based on modal beating. We use modal analysis to explain the two concepts for incorporating this fade-in behaviour entirely within the IIR structure of a multiple input multiple output FDN. We present design equations, which allow for placing the fade-in time at an arbitrary point within its derived limit.

Download

A method is proposed to encode the acoustic scattering of objects for virtual acoustic applications through a multiple-input and multiple-output framework. The scattering is encoded as a matrix in the spherical harmonic domain, and can be re-used and manipulated (rotated, scaled and translated) to synthesize various sound scenes. The proposed method is applied and validated using Boundary Element Method simulations which shows accurate results between references and synthesis. The method is compatible with existing frameworks such as Ambisonics and image source methods.

Download