Ando - A Diagnostic System Measuring Orthogonal.Pdf - Akustyka - pg2464

Journal of Sound and < ibration (2000) 232(1), 231}237

doi:10.1006/jsvi.1999.2695, available online at http://www.idealibrary.com on

A DIAGNOSTIC SYSTEM MEASURING ORTHOGONAL

FACTORS OF SOUND FIELDS IN A SCALE MODEL

OF AUDITORIUM

M. S AKURAI

Graduate School of Science and ¹ echnology , Kobe ; niversity , I Rokkodai , Nada ,

Kobe 657-8501, Japan and > oshimasa Electronic Inc ., 1-58-10 > oyogi ,

Shibuya , ¹ okyo 151-0053, Japan

S. A IZAWA

> oshimasa Electronic Inc ., 1-58-10 > oyogi , Shibuya , ¹ okyo 151-0053, Japan

AND

Y. S UZUMURA AND Y. A NDO

Graduate School of Science and ¹ echnology , Kobe ; niversity , I Rokkodai , Nada ,

Kobe 657-8501, Japan

( Accepted 30 June 1999)

Based on the model of auditory}brain system which consists of the

autocorrelation mechanism, the interaural cross-correlation mechanism between

both the auditory pathways, and the specialization of human cerebral hemispheres

(Y. Ando 1998 Architectural Acoustics , Blending Sound Sources , Sound Fields , and

¸ isteners New York: AIP Press/Springer-Verlag), a new diagnostic system was

developed. After obtaining the binaural impulse response, four orthogonal factors

including the SP ¸, the initial time-delay gap between the direct sound and the "rst

re#ection, the subsequent reverberation time and the IACC can be analyzed for the

calculation of the scale values of both global and individual subjective preferences.

In addition, two more factors extracted from the interaural cross-correlation

function

and =

IACC

, can be "gured out. Also, the sound energy,

(0), the

, and "ne structures of autocorrelation function of sound

signals including the magnitude of "rst maximum,

q e

, can be

analyzed. As an example of the measurement, e!ects of re#ectors' array above the

stage in a 1/10 scale model of auditorium at each seat are discussed here.

(

/ 1

, and its delay time,

q 1

2000 Academic Press

IACC

[1}6] , and also the running ACF of sound "eld at each seat in a scale model as well

as in a real auditorium, a diagnostic system is developed. Based on the model of

D ¹

, ¹

sub

, IACC ,

q IACC

, and =

0022-460X/00/160231#07 $35.00/0

(

2000 Academic Press

q IACC

e!ective duration,

1. INTRODUCTION

In order to measure orthogonal factors, SP ¸,

232

M. SAKURAI E ¹ A ¸.

Figure 1. A model of auditory}brain system.

auditory}brain system which consists of the autocorrelation mechanism, the

interaural cross-correlation mechanism between both the auditory pathways, and

the specialization of human cerebral hemispheres as shown in Figure 1 [1],

a diagnostic system was designed. The system works on PC for Windows with

AD&DA converters; there is no need for special additional devices. After obtaining

the binaural impulse responses, four orthogonal factors including the SP ¸, the

initial time-delay gap between the direct sound and the "rst re#ection, the

subsequent reverberation time and the IACC are analyzed. These factors are used

for the calculation of the scale values of both the global and individual subjective

preferences. In addition to the four factors, two more factors,

q IACC

and =

(0), the e!ective duration,

,de"ned by the delay at which the envelope of normalized ACF becomes 0)1 (see

Figure 3), and "ne structures of autocorrelation function of sound signals including

the magnitude of "rst maximum,

, of source signals are

analyzed. In order to examine e!ects of the re#ectors' array above the stage in a

, and its delay time,

q 1

scale model of auditorium, the IACC measurements are demonstrated here.

2. OUTLINE OF A DIAGNOSTIC SYSTEM

Because the complex requirements made the system di$cult to evaluate, an

advanced diagnostic system and a high-power computer was used. The measuring

system was utilized to obtain the binaural impulse response at each listening

de"ned in Figure 2, extracted from the interaural cross-correlation function can be

"gured out for evaluating the image shift of sound source and the apparent source

width [6] respectively. Also, the averaged sound energy,

IACC

q e

/ 1

A DIAGNOSTIC SYSTEM FOR SOUND FIELDS

233

Figure 2. De"nitions of the IACC ,

q IACC

and =

IACC

in the interaural cross-correlation function.

Figure 3. A practical example of determining e!ective duration of ACF de"ned by the ten-

percentile delay, with the straight line-"tting envelope of ACF from 0 to !5 dB.

scale model of dummy head (a sphere with a diameter of 25 mm) was sampled after

passing through a low-pass "lter (see Figure 4) . The binaural-impulse-response

measurement may be performed by a summation of the output data from the linear

system, without any multiplication operation [7, 8]. The measurement was done

automatically within only a few seconds by pushing a single button. It took another

few seconds for the analysis of the orthogonal acoustic factors and the scale value of

the subjective preference. And at the same time this program can take the result to

compute the acoustic parameters and prepare the reports.

position. The sound was created by using an omni-directional loudspeaker fed with

a maximum length signal produced by a diagnostic system in a notebook PC. The

period of the maximum length signal (MLS) was between 1024 and 524 288

samples, and the sampling rate can be changed between 8 and 48 kHz. The acoustic

signal ampli"ed from the two microphones placed at the entrances of ears of a

234

M. SAKURAI E ¹ A ¸.

Figure 4. A block diagram of the measurement system.

Figure 5. An example of display window of the diagnostic system, with binaural impulse responses.

A DIAGNOSTIC SYSTEM FOR SOUND FIELDS

235

3. MEASUREMENT OF ORTHOGONAL ACOUSTIC FACTORS

3.1. PROCEDURE

The diagnostic system developed may examine e!ects of scattered re#ections of

complex boundary conditions of the room. The re#ectors above the stage are

designed mainly for the performer obtaining the preferred re#ections according to

the program sources. We measured the IACC of the sound "eld at each seat to "nd

the e!ects of the re#ectors' array above the stage [9] . The e!ective direction of

re#ections to listeners for the 2000 Hz range is centered on $183 from the median

plane, which might be realized by a re#ectors above the stage [1] . Therefore, the

IACC of the 2000 Hz frequency band is selected here to be examined.

In order to obtain reliable results, measurements were repeated several times

until the same results for the binaural impulse responses were obtained. The sound

is produced by using an omni-directional loudspeaker fed with the MLS produced

by the diagnostic system in a notebook PC. Figure 5 shows the window on PC of

actual diagnostic system with the data obtained from the impulse responses. In the

measurement, special attention should be paid to maintain a suitable value of the

signal-to-noise ratio adjusting the power level of the loudspeaker.

Figure 6. Measured IACC for the 2000 Hz frequency band with re#ectors above the stage.

Ando - A Diagnostic System Measuring Orthogonal.Pdf

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