Sound Reproduction System Research Articles

5-2-5 Matrix encoder and decoder system

A sound reproduction system has been developed, for converting signals on two input channels into surround signals on five or seven output channels and vice-versa. A decoder is included in the sound reproduction system which enhances the correlated component of the input signals in the desired direction and reduces the strength of such signals in channels not associated with the encoded direction, while preserving the apparent loudness of all output channels, the separation between the respective left and right output channels and the total energy of the uncorrelated component of the input channels in each output channel. The decoder may include a uniquely defined matrix that helps to ensure that the surface of the output signals is smooth and continuous.

Sound recording and reproduction systems

Sound recording and reproduction systems

ヒューマンインタフェースとバーチャルリアリティ 心理・生理計測による音再生システムの客観評価指標の検討

To create a genuine virtual reality space,it is important to develop a high quality system for sound reproduction and to assess the sound quality. However,there has been no objective assessment scale for the sound quality of a system. In this paper,we investigate an objective assessment scale for a sound reproduction system based on psychological and physiological measurement. As a result,it is shown that an activity of the autonomic nervous system may become an objective assessment scale .

Sound reproduction system with switching control band range on every listening point

We propose a robust multichannel sound reproduction system that utilizes the relationship between the width of the actual listening area and the control frequency of the listening points. The conventional multichannel sound reproduction system uses inverse filters that are designed based on room transfer functions (RTFs) from loudspeakers to listening points in the listening room. However, the sound reproduction accuracy is deteriorated by room environment variations when fixed inverse filter coefficients are used because the condition number relevant to the instability of the matrix composed of the RTFs is large, especially at low frequencies; the inverse filters are unstable at those frequencies. This tendency is more remarkable when listening points are arranged more closely. To resolve the problem, we switch the control band at every listening point to avoid degrading the reproduced sound in low‐band frequencies. The control band range of the listening points at both ears is only high band. That of th...

A fundamental investigation of the small microphone array system and its applications

A purpose of this research is to construct a 3‐D sound recording and reproduction system that has a high presence by performing a spatially controlled sound field synthesis technique. For this purpose, it will be required to examine and choose the most suitable sound recording system, since a conventional sound recording system samples only original signal itself, and does not include enough spatial information. In other words, it will be required to examine the system to record the information of the three‐dimensional spaces, such as the direction and the distance, and to transform the configuration to become effective to the reproduction system. This paper will deal with a basic examination to construct the microphone array placed in proximity and the recording system, which is able to control the directivities in the three‐dimensional spaces, using algorithm based on LMS by FIR filter networks from signals to each microphone.

Evaluation of spatial impression of sound in horizontal and depth directions for the purpose of developing an advanced multichannel live sound reproduction system

A prototype of an advanced multichannel live sound reproduction system was developed. In this system, multiple loudspeakers are arranged in the horizontal and depth directions in front of listeners to reproduce a sense of sound depth and width [K. Hamasaki et al., Proc. 119th AES Convention, (2005) p. 6559 ]. Using this prototype, a number of subjective tests were conducted to evaluate the listeners sense of sound depth and width. The results revealed that while the direct sound source was perceived near the predicted horizontal location, the sense of depth varied largely from subject to subject. Another listening test was conducted in which reflections from the upper-front of the listeners were reproduced. Simulated reflections of a virtual space were divided into 11 directional room impulse responses (RIRs). The RIRs were convoluted with individual sound sources (male vocals), and subjects compared their spatial impressions of the sound sources reproduced with and without such reflections. The results of this listening test revealed that the feeling of sound depth was one of the factors of spatial impressions and it increased when the reflections from the upper-frontal direction were reproduced.

Adaptive wave field synthesis with independent radiation mode control for active sound field reproduction: Theory

Sound field reproduction finds applications in music or audio reproduction and experimental acoustics. For audio applications, sound field reproduction can be used to artificially reproduce the spatial character of natural hearing. The general objective is then to reproduce a sound field in a real reproduction environment. Wave field synthesis (WFS) is a known open-loop technology which assumes that the reproduction environment is anechoic. For classical WFS, the room response thus reduces the quality of the physical sound field reproduction. In this paper, adaptive wave field synthesis (AWFS) is analytically investigated as an adaptive sound field reproduction system combining WFS and active control with a limited number of reproduction error sensors to compensate the response of the listening environment. The primary point of this paper is the definition of AWFS. Therefore, the fundamental behavior of AWFS is illustrated by analytical considerations and simple free-field simulation results. As demonstrated, AWFS is fundamentally related to WFS and “Ambisonics.” The paper introduces independent adaptive control of sound field reproduction on the basis of radiation modes, via the singular value decomposition of the transfer impedance matrix. Possible practical independent control of radiation modes for AWFS is discussed.

Loudspeakers and listening rooms, Part II: The perception of reflections

A review of the effects of reflections on perceptions of sound quality, direction, image size, spaciousness, speech intelligibility, etc., lending perspective to the matter of which elements might be perceptually important in multichannel sound reproduction systems. In general they appear to be less problematic than is commonly believed. This, combined with the considerable ability of listeners to adapt to certain auditory influences of small rooms, brings into question several popular practices in the design of loudspeakers and listening rooms. Anechoic measurements on loudspeakers that have been done in a manner that anticipates sound reproduction in rooms can be used to calculate a figure of merit. The correlation between the calculated ratings, and those resulting from double-blind listening tests, is high: 0.86. This has implications for the acoustical treatment of rooms, and to the necessity for controlling the sound field at low frequencies. Only then can there be any assurance that the art in recordings will be heard by consumers as it was created in control rooms.

Method and apparatus for spatially enhancing the stereo image in sound reproduction and reinforcement systems

Sound reproduction and reinforcement systems and methods are presented herein for spatially enhancing stereo images typically used such performances as those involving music. The embodiments seek to expand the amount of audience area that would receive a sound image that maintains sound reproduction fidelity regarding spatial orientation of sound sources involved in an original performance. To expand the audience area receiving spatially faithful sound reproduction certain characteristics of sound have been first studied to find important factors involved.

Surround sound field reproduction system and surround sound field reproduction method

A surround sound field reproduction system and method is disclosed by which, in such a case that a listener changes its posture so that a portion of a video image to which attention should be paid may be observed in front of the listener, a sound image can be localized accordingly in a direction in which the video image is observed in front of the listener. Specifically, the surround sound field reproduction apparatus includes a plurality of horizontal panners for receiving a plurality of sound signals from microphones disposed horizontally and cooperating with each other to control the horizontal localization, and a vertical panner for receiving sound signals from microphones disposed vertically to control the vertical localization. The horizontal panners level-distribute the received sound signals to a plurality of output channels provided corresponding to surround reproduction output channels. The vertical panner changes the level distribution of the sound signals in the vertical direction to produce a sound signal and outputs the produced sound signal to an output channel for the front center.

Optimal source distribution

A sound reproduction system has pairs of sound emitters that subtend different angles Θ, the span angle, at the listener position. The pairs of sound emitters are arranged to be excited by different frequency bands of the signal output from an inverse filter means (H h , H l ). The operational span-frequency range of the pairs of sound emitters is determined by an equation (I) where the transducer span Θ is the angle subtended at the listener by a pair of transducers, where O<n<2. c 0 : is the speed of sound, and Δr: is the equivalent distance between the ears. The sound emitters may be discrete speaker units, the different pairs of units being positioned at different span angles, or they be constituted by area portions of an extended transducer (FIG. 10 ). When discrete speaker units are employed a cross-over filter (FIG. 28 ) is used to provide drive signals in the different frequency bands to the different speaker pairs. When an extended transducer is employed, the vibration transmission characteristics of the transducer may be arranged to filter the vibrations transmitted along the transducer from an excitation means positioned at the higher frequency emitting end of the transducer.

Transducer sensitivity compensation using diagonal preconditioning for time reversal and Tikhonov inverse filtering in acoustic systems

Filters are commonly used in sound reproduction and communication systems as a means of compensating for the response of the electro-acoustic plant. Two commonly used filter designs in the field of acoustics are the time reversal filter and the Tikhonov inverse filter. In this paper the influence of transducer sensitivities on the performance of these filters is examined. It is shown that the sensitivity of the transducers can negatively affect the performance of the resulting filter. To compensate for the decrease in performance, diagonal preconditioning can be implemented in the system. It is shown that by using diagonal matrices, which minimize the condition number of the system, the loss in performance arising from unbalanced sensitivities is minimized. This paper proposes an algorithm to find such a set of diagonal matrices and results are presented showing the improvements in performance arising from the modified filter design.

Apparatus and method for multichannel sound reproduction system

The sound reproduction of a multichannel sound reproduction system with a plurality of speakers which is connected to the output of an FM stereo receiver is controlled by a control signal derived from the reception quality. Preferably, the control signal from the FM stereo receiver for controlling the stereo and mono components is also employed to control the multichannel sound reproduction system. For example, stereo, pseudo-stereo or mono reproduction are provided in the multichannel sound reproduction system in response to the stereo component within the output signal.

On-Line Relaxation Algorithm Applicable to Acoustic Fluctuation for Inverse Filter in Multichannel Sound Reproduction System

In this paper, we propose a new on-line adaptive relaxation algorithm for an inverse filter in a multichannel sound reproduction system. The fluctuation of room transfer functions degrades reproduced sound in conventional sound reproduction systems in which the coefficients of the inverse filter are fixed. In order to resolve this problem, an iterative relaxation algorithm for an inverse filter performed by truncated singular value decomposition (adaptive TSVD) has been proposed. However, it is difficult to apply this method within the time duration of the sound of speech or music in the original signals. Therefore, we extend adaptive TSVD to an on-line-type algorithm based on the observed signal at only one control point, normalizing the observed signal with the original sound. The result of the simulation using real environmental data reveals that the proposed method can always carry out the relaxation process against acoustic fluctuation, for any time duration. Also, subjective evaluation in the real acoustic environment indicates that the sound quality improves without degrading the localization.

The effects of acoustical treatment on lateralization of low-frequency sources

Recently, the standard of using a single low-frequency driver in stereophonic sound reproduction systems has come into question. Though it is accepted that lateral discrimination and localization of signals is possible well into the subwoofer frequency range, the use of multiple subwoofers in small reverberant rooms remains of questionable value. While inter-aural level differences (ILDs) are negligible at low frequencies, source lateralization is possible at low frequencies by virtue of inter-aural time differences (ITDs). But when such reproduction is attempted in small rooms, strong early reflections and resonances associated with room modes can cause erroneous ITD information to be detected by a listener, thereby compromising a listener’s ability to accurately locate the source of a low-frequency sound. Acoustical treatment can be employed to reduce the level of early reflections and low-frequency ringing associated with sharp resonant modes in small rooms. Such acoustical treatment often results in more accurate reproduction of ITDs, which enables more accurate localization of sound sources in the horizontal plane. This study investigated changes in measured interaural phase differences after a treatment scheme using both diaphragmatic and Helmholtz-style absorbers. The results show the viability of using multiple low-frequency drivers given adequate acoustical treatment of the reproduction space.

Acoustic reproduction device with improved directional characteristics

A sound reproduction system is disclosed which minimizes unwanted acoustic reflections and the resulting comb-filter effects but which still maintains a broad and uniform directional characteristic throughout the region in the listening room in which listening positions are located.

Hearing aid with adaptive noise canceller

A noise reduction system for a sound reproduction system, in particular for hearing aids, comprises a primary and a secondary microphone for producing input signals in response to sound in which a noise component is present. The system has a first signal processing section comprising a fixed filter and a summing function, wherein the first signal processing section has means for receiving signals from the microphones and producing a speech reference signal and a noise reference signal. A second signal processing section comprises an adaptive filter and an additional summing function, and the second signal processing section has means for receiving the speech and noise reference signals and producing an output signal with an improved signal-to-noise ratio.

Headphones with integrated microphones

A sound reproduction system comprises headphones (11). Said headphones comprise means for generating sound (4, 5) and microphones (6, 7) (i.e. means for recording sound). Further the system comprises filter means (8,9) to filter a signal such that the sound produced simulates external sound sources. The system comprises a feed-back and control system (10) in which a signal (rl(k), rr(k)) from the microphone (6, 7) is used to set the settings WXL(k), WXR(k) of the filter means (8,9).

The Gauss‐Seidel fast affine projection algorithm for multichannel active noise control and sound reproduction systems

AbstractIn the field of adaptive filtering, the fast implementations of affine projection algorithms are known to provide a good tradeoff between convergence speed and computational complexity. Such algorithms have recently been published for multichannel active noise control systems. Previous work reported that these algorithms can outperform more complex recursive least‐squares algorithms when noisy plant models are used in active noise control systems. This paper proposes a new fast affine projection algorithm for multichannel active noise control or sound reproduction systems, based on the Gauss–Seidel solving scheme. The proposed algorithm has a lower complexity than the previously published algorithms, with the same convergence speed and the same good performance with noisy plant models, and a potential for better numerical stability. It provides the best performance/cost ratio. Details of the algorithm and its complexity are presented in the paper, with simulation results to validate its performance. Copyright © 2004 John Wiley &amp; Sons, Ltd.

Perceptual evaluation of multi-dimensional spatial audio reproduction

Perceptual differences between sound reproduction systems with multiple spatial dimensions have been investigated. Two blind studies were performed using system configurations involving 1-D, 2-D, and 3-D loudspeaker arrays. Various types of source material were used, ranging from urban soundscapes to musical passages. Experiment I consisted in collecting subjects' perceptions in a free-response format to identify relevant criteria for multi-dimensional spatial sound reproduction of complex auditory scenes by means of linguistic analysis. Experiment II utilized both free response and scale judgments for seven parameters derived form Experiment I. Results indicated a strong correlation between the source material (sound scene) and the subjective evaluation of the parameters, making the notion of an "optimal" reproduction method difficult for arbitrary source material.