Reverberation design based on acoustic parameters for reflective audio-spot system with parametric and dynamic loudspeaker

Transcription

1 PROCEEDINGS of the 22 nd International Congress on Acoustics Signal Processing Acoustics: Paper ICA Reverberation design based on acoustic parameters for reflective audio-spot system with parametric and dynamic loudspeaker Ryosuke Uemura (a), Tomoyuki Wada (b), Takahiro Fukumori (c), Masato Nakayama (d), Takanobu Nishiura (e) (a, b) Graduate School of Information Science and Engineering, Ritsumeikan University, JAPAN, (c, d, e) College of Information Science and Engineering, Ritsumeikan University, JAPAN, Abstract A three-dimensional sound field reproduction system is required in the field of the entertainment. We have previously proposed the three-dimensional sound field reproduction system using the parametric loudspeaker which represents the sound image with a high accuracy. This method can design the sound image for the target by reflecting the sound emitted from the parametric loudspeaker. This designed sound image is called reflective audio-spot. However, this method has a problem that the parametric loudspeaker can t represent the room reverberation. Therefore, we have previously proposed the method using the parametric and dynamic loudspeakers to represent the room reverberation. This method controls the room reverberation on the basis of the reverberation time. However, the room reverberation has not only the reverberation but also various acoustic parameters. These acoustic parameters are important for the human perception at room positions. In this paper, we therefore propose the reverberation design based on acoustic parameters for the reflective audio-spot system using parametric and dynamic loudspeakers. In the proposed method, we utilize the reverberation time and the direct-to-reverberant ratio to perceive the sensation of the listener position in the room. We confirmed the effectiveness of the proposed method through the evaluation experiment. Keywords: Three-dimensional sound field reproduction, Parametric loudspeaker, Dynamic loudspeaker, Reverberation time, Direct-to-reverberant ratio

2 Reverberation design based on acoustic parameters for reflective audio-spot system with parametric and dynamic loudspeaker 1 Introduction A three-dimensional sound field reproduction system can provide listeners with a sense of presence. A binaural and a transaural systems [1, 2] have been proposed as the threedimensional sound field reproduction system. Although the binaural system can reproduce the sound field by using the head-related transfer function of listeners, they feel troublesomeness because this system forces listeners to use a headphone. On the other hand, the transaural system can reproduce the sound field by utilizing inverse filters with multiple remoteloudspeakers. However, it requires a large-scale system with a lot of loudspeakers and high computational costs. We have previously proposed the three-dimensional sound field reproduction system using the parametric loudspeaker [3] ~ [5] which represents the sound image with a high accuracy. This method can design the sound image for the target by reflecting the sound emitted from the parametric loudspeaker. This designed sound image is called reflective audio-spot. However, this method has a problem that the parametric loudspeaker can t represent the room reverberation. Therefore, we have previously proposed the method using the parametric and dynamic loudspeakers to represent the room reverberation. This method controls the room reverberation on the basis of the reverberation time [6]. However, the room reverberation has not only the reverberation but also various acoustic parameters. These acoustic parameters are important for the human perception at room positions. In this paper, we therefore propose the reverberation design based on acoustic parameters for the reflective audio-spot system using parametric and dynamic loudspeakers. In the proposed method, we utilize the reverberation time and the direct-to-reverberant ratio (DRR) to perceive the sensation of the listener position in the room. 2 Three-dimensional sound field reproduction system using parametric loudspeaker and indirect dynamic loudspeakers We have previously proposed the method using the parametric and dynamic loudspeakers to represent the room reverberation as shown in Fig. 1. The indirect dynamic loudspeaker is an dynamic loudspeaker for representing an indirect sound such as an indirect illumination that represents indirect light. In Fig. 1, this system represents the sound image from the parametric loudspeaker and the reverberation from indirect dynamic loudspeakers. This method controls the room reverberation on the basis of the reverberation time. Then, we measure the impluse response at the listening point and design the filter which propagates the reverberation time in this point. Here, this filter h(t) is derived as follows: 2

3 Figure 1: Overview of the three-dimensional sound field reproduction system using the parametric loudspeaker and indirect dynamic loudspeakers h(t) = w(t) exp ( αt), (1) where t is a time index, w(t) is a white noise, α is a constant of an exponential slope corresponding to the desired reverberation time. This conventional method convolves the filter and the sound source, and realizes desired reverberation time by emitting this sound from the indirect dynamic loudspeaker. However, this method can imperfectly reproduce reververant environments because the room reverberation has not only the reverberation but also various acoustic parameters. These acoustic parameters are important for the human perception at room positions. 3 Proposed method 3.1 Principle of proposed system As mentioned previously, the conventional method has a difficulty to reproduce reverberant environments with a high accuracy. Therefore, in the proposed method, we utilize the reverberation time and the DRR influenced the perception of the distance example of the sound source and a wall. Figure 2 indicates the component of the three-dimensional sound field production with the proposed method. In Fig. 2, this method measures the impulse response in the target sound field by designing the reverberation control filter. In addition, we measure the impulse response in the whole room. This method arranges control points to control the reverberation in the whole room. Reverberation control filters are designed adaptively using the reverberation time and DRR. Here, the DRR is derived as follows: 3

4 Figure 2: Component of the three-dimensional sound field reproduction with the proposed method DRR = 10 log 10 ( τ 1 t=0 h2 (t) T 1 t=τ h 2 (t) ), (2) where τ is a duration time of the direct sound, T is a length of the sound signal, and h(t) is a reverberation control filter. The proposed method calculates the ratio of the reverberation for the direct sound. Finally, each indirect dynamic loudspeaker emit the sound convolved the reverberation control filter and given the delay time. Then, the target sound field is reproduced by emitting the amplitude modulated (AM) wave from the parametric loudspeaker. Even if the target listener is everywhere, this method can reproduce reverberant environments by controling the reverberation time in the whole room. 3.2 Reverberation control in whole room based on acoustic parameters The proposed method reproduces the reverberation in the target sound field by controlling the reverberation in the whole room based on reverberation time and the DRR Design of reverberation control filters based on reverberation time Figure 3 indicates the block diagram of designed reverberation control filters based on the reverberation time. In Fig. 3, t is a time index, l(= 1,2,, L) is the number of the control point, m(= 1,2,, M) is the number of indirect dynamic loudspeakers, i is the iteration number of times of reverberation control filters based on the reverberation time, MIC l is control points, SP 0 is the parametric loudspeaker, SP m is indirect dynamic loudspeakers, h m,i (t) is the reverberation control filter based on the reverberation time, g l,0 (t) is the impulse response between the 4

5 Figure 3: Block diagram of designed reverberation control filters based on the reverberation time control point and the parametric loudspeaker, g l,m (t) is the impulse response the control point and the indirect dynamic loudspeaker, o l (t) is the observed signal in the control point, d is the desired reverberation time, r l is the reverberation time calculated in the control point, e l is the error between the calculated reverberation time and the desired reverberation time, w l is the weight vector and e is the weighted average vector. Here, iteration equations are derived as follows: h m,i+1 (t) = w(t) exp ( α m,j+1 t), (3) α m,i+1 = α m,j + μ e m, (4) α m,0 = 0, (5) where μ is the step size, α m,i is the parameter of h m,i (t). In the proposed method, reverberation control filters are modified by the iteration equation based on the error of the reverberation time Design of Reverberation Control Filters Based on DRR Figure 4 indicates the block diagram of designed reverberation control filters based on the DRR. In Fig. 4, j is the iteration number of times of reverberation control filters based on the DRR, h m,i (t) is the reverberation control filter based on the DRR, o l (t) is the observed signal in the control point, d l is the DRR calculated in the control point, d l is the desired the DRR in the control point, e l is the error between the calculated DRR and the desired the DRR, and ê l is the weighted average vector. Here, iteration equations are derived as follows: ĥ m,j+1 (t) = p m,j+1 (t) + h m,opt (t), (6) p m,j+1 (t) = p m,j (t) β e m, (7) h m,opt (t) = w(t D) exp ( α m,i (t D)), (8) 5

6 Figure 4: Block diagram of designed reverberation control filters based on DRR where I is the iteration number of times, β is the iteration parameter of the reverberation control filter based on the DRR, h m,opt (t) is the reverberation filter given the delay time at h m,i (t), and D is the delay time. In the proposed method, each indirect dynamic loudspeaker emit the sound convolved the designed filter. In addition, the proposed method can reproduce the desired reverberation time and the DRR by emitting the AM wave from parametric loudspeaker. 4 Evaluation Experiment In the proposed method, the parametric loudspeaker represents a sound image, and indirect dynamic loudspeakers represent a reverberation. Therefore, we carried out evaluation experiments on the performance of the sound image localization, the reverberation time and the DRR to confirm the effectiveness of the proposed method. 4.1 Experimental Conditions Table 1 indicates experimental conditions, and Fig. 5 indicates experimental arrangements. This experiment utilizes the parametric loudspeaker and six indirect dynamic parametric loudspeakers as shown in Fig. 5. An impulse response was recording using the dummy head in advance. In the evaluation of the sound image localization, we utilize the Inter-Aural Cross Coefficient (IACC). The IACC represents the correlation of acoustic signal arriving at left and right ears. It is based on the normalized Inter-Aural Cross Function (IACF) [7]. Here, the IACF and the IACC are derived as follows: IACF t1,t 2 (τ) = t2 p l(t) p r (t+τ) t=t1, (9) t2 p 2 l (t) t2 p2 t=t1 t=t1 r (t) IACC t1,t 2 = max IACF t1,t 2 (τ), τ 1 [ms], (10) where t is a time index, t 1 and t 2 are the measured time, p l (t) is the acoustic signal arriving at left ear, p r (t) is the acoustic signal arriving at right ear, and τ is the delay time. Next, in the evaluation of the reverberation time, we utilize the error between the calculated reverberation time using the proposed method and that using the target sound field. Here, the error of the reverberation time e rtime is derived as follows: 6

7 Table 1: Experimental conditions Carrier frequency 40 [khz] Sound source TSP (2 20 [point]) Sampling frequency 192 [khz] / 16 [bit] Reverberation time of the room T 60 =0.4 [s] Ambient noise level 43.1 [db] Temperature / Humidity 13 [ ] / 15 [%] Figure 5: Experimental arrangements e rtime = max t reproduced t target 100, (11) where t reproduced is the calculated reverberation time using the conventional and proposed methods, and t target is the calculated reverberation time using the target sound field. Finally, in the evaluation of the DRR, we utilize the error between the calculated DRR using the proposed method and that using the target sound field. Here, the error of the DRR e drr is derived as follows: r reproduced r target e drr = , (12) where r reproduced is the calculated DRR using the conventional and proposed methods, and r target is the calculated DRR using the target sound field. In addition, we also carried out the subjective experiment the same. The subjective experiment utilizes the evaluation sheet as the evaluation method of the sound image localization as shown in Fig. 6. Table 2 indicates evaluation scales of the reverberation time and the DRR. 4.2 Experimental results Figure 7 indicates the experimental result of the sound image localization. In Fig. 7(a), the horizontal axis indicates directions of arrival, the vertical axis indicates the average error of the angle, and the error bar is the standard deviation. In Fig. 7(b), the horizontal axis indicates the presented angle, the vertical axis indicates the answered angle, the solid line indicates the 7

8 Figure 6: Evaluation sheet Table 2: Evaluation scales of the reverberation time and DRR Length of the sound Sense of the distance from the wall 5 Long Far 4 Slightly long Slightly far 3 Same extent Same extent 2 Slightly short Slightly near 1 Short Near reproduced drection, and the dotted line indicates the perception error between the front and the rear. Most error of the sound image localization are less than 5 [deg] as shown in Fig. 7, and the conventional and proposed methods can exactly reproduce the sound image. However, the error of 60 [deg] can t exaclty reproduce the sound image because the sound image was localized at the position of the indirect dynamic loudspeaker. Figure 8 indicates the experimental result of the reverberation time. In Fig. 8(a), the horizontal axis indicates directions of arraival, the vertical axis indicates the average error of the reverberation time, and the error bar is the standard deviation. In Fig. 8(b), the horizontal axis indicates directions of arrival and the vertical axis indicates the score of the reverberation time. The conventional and proposed methods can reproduce the reverberation time of the target sound field in evaluation points because it is less than 7 [%] considered to be a difference threshold. Figure 9 indicates the experimental result of the DRR. In Fig. 9(a), the horizontal axis indicates directions of arraival, the vertical axis indicates the average error of the DRR, and the error bar is the standard deviation. In Fig. 9(b), the horizontal axis indicates directions of arraival and the vertical axis indicates the score of the distance from the wall. The proposed method can reproduce the DRR exactly compared with the conventional method because the error with the proposed method is less than it with the conventional method. As three results of evaluation experiments, we could confilm the effectiveness of the proposed method. 8

9 (a) Objective experiment (b) Subjective experiment Figure 7: Experimental result of the sound image localization (a) Objective experiment (b) Subjective experiment Figure 8: Experimental result of the reverberation time (a) Objective experiment Figure 9: Experimental result of the DRR (b) Subjective experiment 9

10 5 Conclusions In this paper, we therefore proposed the reverberation design based on acoustic parameters for the reflective audio-spot system using parametric and dynamic loudspeakers. As results of evaluation experiments, we confirmed the effectiveness of the proposed method. In future work, we will attempt to reproduce multiple sound images and the other sound field. Acknowledgments This work was partly supported by COI and JSPS KAKENHI Grant Numbers JP ,JP ,JP15K References [1] Moller, H. Fundamentals of binaural technology, Applied Acoustics, Vol 36 (3-4), 1992, pp [2] Bauck, J.; Cooper, H. D. Generalized transaural stereo and applications, Journal of the Audio Engineering Society, Vol 44 (9), 1996, pp [3] Sugibayasi, Y.; Kurimoto, S.; Ikefuji, D.; Morise, M.; Nishiura, T. Three-dimensional acoustic sound field reproduction based on hybrid combination of multiple parametric loudspeaker and electrodynamic subwoofer, Applied Acoustics, Vol 73 (12), 2012, pp [4] Yoneyama, M.; Fujimoto, J.; Kawamo, Y.; Sasabe, S. The audio spotlight: An application of non-linear interaction of sound waves to a new type of loudspeaker design, The Journal of the Acoustical Society of America, Vol 73 (5), 1983, pp [5] Westervelt, J. P. Parametric acoustic array, The Journal of the Acoustical Society of America, Vol 35 (4), 1963, pp [6] Kuttruff, H. Room Acoustics, Elsevier Science Publishers Ltd, London (UK), first edition, [7] Fujii, K.; Soeta, Y.; Ando, Y. Acoustical properties of aircraft noise measured by temporal and spatial factors, Journal of Sound and Vibration, Vol 241 (1), 2001, pp