Civil Engineering Reference
In-Depth Information
in the first 50 or 80 milliseconds to the rest of the energy received. We have an
early-to-
late index
C
t
e
defined by
⎛
⎞
t
∞
e
⎜
t
⎟
∫
2
∫
2
C
=⋅
10 lg
p
( ) d
t
t
p
( ) d
t
⎟
,
(4.4)
t
⎝
e
⎠
0
t
e
where
t
e
is 50 ms for speech and 80 ms for music. A recommended value for this
parameter is 0 dB.
An early variant of this parameter was
D
50
, which is denoted
definition
in line with
the original German notion of
Deutlichkeit.
The difference from the above is that, instead
of the late energy, one is using the total energy received. Hence
50ms
∞
=
∫
∫
2
2
D
p
()d
t
t
p
()d.
t
t
(4.5)
50
0
0
The relationship between
C
50
and
D
50
is then given by
⎛
D
⎞
50
C
=⋅
10 lg
⎟
,
(4.6)
⎜
50
1
−
C
⎝
50
making it unnecessary to measure both parameters.
By way of introduction, we pointed out that the direction of sound incidence was
important for the feeling of spaciousness. Of special importance are the lateral
reflections, which also contribute to an impression of widening a source or a source area.
Several early lateral energy measures are proposed, one is the
lateral energy fraction LF
based on measured impulse responses obtained from an omni-directional and a figure-of-
eight pattern microphones. It is defined as
80ms
80ms
=
∫
2
∫
2
LF
p
()d
t
t
p
()d,
t
t
(4.7)
L
5ms
0
where
p
L
is the sound pressure obtained with the figure-of-eight microphone. This
microphone is intended to be directed in such a way that it responds predominantly to
sound arriving from the lateral directions and is not significantly influenced by the direct
sound.
Because the directivity of a figure-of-eight microphone essentially has a cosine
pattern and the pressure is squared, the resulting contribution from a given reflection will
vary with the square of the cosine of the angle between the reflection relative to the axis
of maximum sensitivity of the microphone. An alternative parameter is
LFC
, where the
contributions will be a function of the cosine to this angle. This parameter, which is
believed to be subjectively more accurate, is defined by
80ms
80ms
∫
∫
2
LFC
=
p
()
t
⋅
p t
()d
t
p
()d.
t
t
(4.8)
L
5ms
0
