Civil Engineering Reference
In-Depth Information
have a bandwidth Δ
f
≈ 0.71⋅
f
0
and a one-third-octave band a bandwidth Δ
f
≈ 0.23⋅
f
0
. As
mentioned above, specifications for such filters are given in IEC 61260.
p
(
t
)
p
(
t
,
f
0
,
Δ
f
)
3
3
2
2
Δ
f
1
1
0
0
-1
-1
f
0
-2
-2
-3
0
0.01
0.02
0.03
0.04
0.05
-3
0
0.01
0.02
0.03
0.04
0.05
t
t
L
p
Equation (1.24)
f
0
f
Figure 1.12
Frequency analysis of a sound pressure signal using fixed filters of bandwidth Δ
f
. A filter having a
centre frequency
f
0
is indicated.
We shall also give a specific example of such analysis using these two types of
band pass filter.
Figure 1.13
shows the result of the analysis on a signal which could
represent the sound pressure measured at a certain distance from a given source. In
addition to the sound pressure levels using these filters, analysis is performed using a
discrete Fourier transform as described in section
1.4.4
.
100
90
1/1
80
1/3
70
DFT
60
50
40
100
1000
60
200
500
2000
5000
Frequency (Hz)
Figure 1.13
Stochastic noise signal with added pure tone components. Analysis in octave bands (1/1) and one-
third-octave bands (1/3) together with discrete Fourier transform analysis (DFT).
