Yoshinari Yamada’s research while affiliated with Samsung R&D Institute Japan and other places

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Publications (3)

A new definition of boundary point between early reflections and late reverberation in room impulse responses
  • Article

August 2007

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256 Reads

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65 Citations

The Journal of the Acoustical Society of America

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Yoshinari Yamada

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Takehiko Nakagawa

The early reflections in the room impulse response are usually defined as those observed within the initial 80 ms after the arrival of the direct sound, after which time the sound field is called reverberant. This number was chosen from measurements of other functions in a limited number of halls. In order to give an objective foundation to this time separation and to establish a physical indicator for it, a new method is proposed that defines a "transition time t(L)," which is the time at which the energy correlation between the direct plus initial sound and the subsequent decaying sound first achieves a specified low value. For various halls this number is shown and its relevance as a new parameter is discussed.

Fig. 1. Block diagram of experimental setup and synthesis of test signal.
Fig. 4. Threshold level measured with additional reflection (arrow) along with that of single reflection (open circle) and the envelope of test signal. Error bar is the standard deviation.  
Fig. 6. An example of RMS output signals from the identified RC circuit, and definitions of EI and CEI. Input signal is the envelope of a reftectogram in a real hall.
Fig. 7. Relationship between score and CEI for the hall Dl.  
Fig. 8. Same as Fig. 7 but for four halls. Enclosed data arc singular cases in which repetitive reflection or discontinuity of reverberation was observed.  

+2

A simple method to detect audible echoes in room acoustical design
  • Article
  • Full-text available

September 2006

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165 Reads

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2 Citations

Applied Acoustics

Yoshinari Yamada

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Yôiti Suzuki

A simple method to detect audible echoes is proposed as an objective criterion for room acoustics. This method evaluates the perceptibility of sound reflections that are generated by an impulsive sound source and identifies from reflectograms harmful reflections perceived as echoes. Particularly with this method, the masking effect of reverberation is taken into consideration, which cannot be treated sufficiently by the existing objective criteria. The applicability to room acoustical design is verified by evaluating the impulse responses measured in real halls where audible echoes occurred. It is shown that the proposed method detects audible echoes at an accuracy of more than 90% and would be suitable for practical use.

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FIG. 5. Same as Fig. 4 but for different condition. FIG. 6. Same as Figs. 4 and 5 but for different condition.
FIG. 8. Focusing effect of circular, parabolic, and elliptic cylinders: a L amp of circular cylinder as a function of the radius to wavelength ratio a −1 , the parameter is the included angle; b difference with L amp of parabolic and elliptic cylinders as a function of included angle, the parameter is the eccentricity = 1 for parabolic cylinders.
FIG. 10. Same as Fig. 9 but for different source position. FIG. 9. Spatial distribution of reflected sound from four cylinders with 10 m radius and included angle of 90°: a circular, b parabolic, c elliptic eccentricity 0.67, and d hyperbolic cylinder eccentricity 1.25. Average value of L amp over one octave bandwidth for midfrequency of 500 Hz is presented as contour lines together with source position circle, the shadow boundaries broken line, and the caustics solid line.
FIG. 11. Same as Figs. 9 and 10 but for different source position. FIG. 12. Same as Fig. 9 but for included angle of 60° and the midfrequency 250 Hz.
FIG. 15. Plot of L amp averaged over one octave bandwidth vs the receiver distance to radius ratio s r / a, for circular cylinder with the included angle 10°. Upper: the source distance is s 0 =2a; lower: the source distance is s 0 = a / 3. The radius to wavelength ratio a −1 is a 60, b 235, c 941, and d .

+3

Reflection of a spherical wave by acoustically hard, concave cylindrical walls based on the tangential plane approximation

August 2005

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357 Reads

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7 Citations

The Journal of the Acoustical Society of America

Yoshinari Yamada

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The tangential plane approximation (TPA) is introduced to investigate the spherical wave reflection from smooth concave cylindrical walls, and as a practical calculation scheme, asymptotic expression of the reflected sound from that surface with a relatively large dimension is derived. The physical condition under which TPA holds is derived for the spherical wave incidence; moreover, the essential properties of the reflected sound from the curved walls, which cannot be treated by the geometrical acoustics, are discussed through the numerical calculation for infinitely long cylinders. A formula of the reflection factor of the two-dimensional curved surface is obtained for the purpose of the room acoustical design. This formula coincides with that based on the geometrical acoustics when the frequency is infinitely high.

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Citations (3)

... However, until now, in the general case the usage of the GTD succeeded only for single reflection, because of too complex mathematical formulas arising in frames of the GTD. If for reflection from an arbitrary absolutely rigid and absolutely smooth surface a certain, at least sufficiently small, vicinity of the mirror reflection point * = ( 1 * , 2 * , 3 * ) ∈ is fully visible from the point source 0 = ( 1 0 , 2 0 , 3 0 ), being also visible from the receiving point = ( 1 , 2 , 3 ), and if the harmonic wave of the unit amplitude generated by the point source is of the form exp[ ( − )]∕ as a function of distance , then theoretically with → ∞ the following general expression for the acoustic pressure at the receiving point takes place (see Fig. 1 Here is the wave number, 1 and 2 are principal curvatures of the surface at the reflecting point * , 0 and are the distances from the source and the receiver, respectively, to the point of mirror reflection * , = 1 2 is the Gaussian curvature of the surface at the reflecting point * , 2 is the sign, i.e. the difference between the number of positive and negative eigenvalues of the symmetric matrix 2 of dimension 2 × 2: 2 = ⎛ ⎜ ⎜ ⎝ 11 12 12 22 ⎞ ⎟ ⎟ ⎠ , 11 = ( 0 + ) sin 2 + 2 0 1 cos , 12 = −( 0 + ) cos cos , 22 = ( 0 + ) sin 2 + 2 0 2 cos . ...

Reference:

Explicit short-wave representations and Ray Tracing method for reflections from curved surfaces in room acoustics
Reflection of a spherical wave by acoustically hard, concave cylindrical walls based on the tangential plane approximation

The Journal of the Acoustical Society of America

Yoshinari Yamada

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... There are uncertainties related to both the lower and upper limit of reflection delay that are detrimental to clarity. Based on these findings, forward integrated impulse responses have been calculated, as used by Yamada, Hadaka and Suzuki to detect audible echoes [18]. The forward integration is performed by integrating the squared pressure impulse response with an exponential decaying integration function. ...

Reference:

Early subjective and objective studies of concert hall stage conditions for orchestral performance
A simple method to detect audible echoes in room acoustical design

Applied Acoustics

Yoshinari Yamada

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Yôiti Suzuki

... where, t m is the approximate mixing time as given by [45] and calculated as t m = 80 · RT 500Hz . w n (t) is the first half of a Hanning window of 0.2 ( 2 · t w ) s and w e (t) is the later half of the window. ...

Reference:

An end-to-end approach for blindly rendering a virtual sound source in an audio augmented reality environment
A new definition of boundary point between early reflections and late reverberation in room impulse responses
  • Citing Article

  • August 2007

The Journal of the Acoustical Society of America

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Yoshinari Yamada

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Takehiko Nakagawa