ba 7660-06, 1 basic frequency analysis of sound contents: frequency and wavelength frequency...
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BA 7660-06, 1
Basic Frequency Analysis of Sound
Contents: Frequency and Wavelength Frequency Analysis Perception of Sound
BA 7660-06, 2
[Hz]1 10 100 1000 10 000
Frequency
Frequency Range of Different Sound Sources
BA 7660-06, 3
1 10 100 1000 10 000 [Hz]
Frequency
Audible Range
BA 7660-06, 4
Wavelength, [m]
Speed of sound, c = 344 m/s
Wavelength
BA 7660-06, 5
c
f
20 10 5 2 1 0.2 0.1 0.05
10 20 50 100 200 500 1 k 2 k 5 k 10 k
Frequency, f [Hz]
Wavelength, [m]
Wavelength and Frequency
BA 7660-06, 6
b
Diffraction of Sound
Example:
b = 1 m
= 0.344 m (f = 1 kHz)
Example :
b = 0.1 m
= 0.344 m (f = 1 kHz)
b
b b
BA 7660-06, 7
Example:
b = 0.5 m
= 0.344 m (f = 1 kHz)
b b
Example :
b = 0.1 m
= 0.344 m (f = 1 kHz)
b bDiffusion of Sound
BA 7660-06, 8
Imaginary Source
Source
SourceSource
Reflection of Sound
BA 7660-06, 9
Basic Frequency Analysis of Sound
Contents: Frequency and Wavelength Frequency Analysis Perception of Sound
BA 7660-06, 10
p Lp
time
Frequency
time
time
p
p
Lp
FrequencyLp
Frequency
Waveforms and Frequencies
BA 7660-06, 11
p Lp
time
Frequency
time
time
p
p
Lp
FrequencyLp
Frequency
Typical Sound and Noise Signals
BA 7660-06, 12
FastSlow
Impulse
87.2
RMSPeakTime
pFrequency
Lp
Frequency
Lp
Time
p
Filters
BA 7660-06, 13
B0
0
- 3 dB
Frequency Frequency
Frequency
Ideal filter
Practical filter anddefinition of 3 dB Bandwidth
Ripple
f1 f0 f2
f1 f0 f2
=
Bandwidth = f2 – f1
Centre Frequency = f0
f1 f0 f2
Practical filter anddefinition of Noise Bandwidth
Area Area
Bandpass Filters and Bandwidth
BA 7660-06, 14
0 1k 2k 3k 4k 5k 6k 7k 8k 9k 10k
B = 400 Hz
Linear Frequency Axis(primarily used in vibration analysis)
2 4 8 16 31.5 63 125 250 500 1k 2k 4k 16k8kFrequency[Hz]
Logarithmic Frequency Axis(primarily used in acoustic analysis)
B = 400 Hz B = 400 Hz
B = 1/1 Octave B = 1/1 Octave B = 1/1 Octave
Frequency[Hz]
L
L
1
Filter Types and Frequency Scales
BA 7660-06, 15
Frequency[Hz]f1 = 891
f0 = 1000
f2 = 1120
f f2 12
B f 0 7 70%0.
f f f23
1 12 125 .
B f 0 23 23%0.
B = 1/1 Octave
f1 = 708
f0 = 1000
f2 = 1410
B = 1/3 Octave
Frequency[Hz]
L
L
1/1 Octave
1/3 Octave
1/1 and 1/3 Octave Filters
BA 7660-06, 16
500 1000 2000
800 1000 1250
L
L
Frequency[Hz]
Frequency[Hz]
B = 1/1 Octave
B = 1/3 Octave
3 × 1/3 Oct. = 1/1 Oct.
BA 7660-06, 17
Band No. Nominal CentreFrequency Hz
Third-octavePassband Hz
OctavePassband Hz
123456
1.251.62
2.53.15
4
1.12 – 1.411.41 – 1.781.78 – 2.242.24 – 2.822.82 – 3.553.55 – 4.47
1.41 – 2.82
2.82 – 5.62
272829303132
500630800
100012501600
447 – 562562 – 708708 – 891891 – 1120
1120 – 14101410 – 1780
355 – 708
780 – 1410
40414243
10 K1.25 K16 K20 K
8910 – 1120011.2 – 14.1
14.1 – 17.8 K17.8 – 22.4 K 11.2 – 22.4 K
Third-octave and Octave Passband
BA 7660-06, 18
L
Frequency[Hz]
1/1 Octave
1/3 Octave
The Spectrogram
BA 7660-06, 19
Basic Frequency Analysis of Sound
Contents: Frequency and Wavelength Frequency Analysis Perception of Sound
BA 7660-06, 20
Infra Audio Ultra
0.02 0.2 2 20 200 2000 20.000 200K HzFrequency
Sound Frequencies
BA 7660-06, 21 960423
140
dB120
100
80
60
40
20
0
20 50 100 200 500 1k 2k 5k 10k 20 kFrequency [Hz]
Sou
nd P
ress
ure
Leve
l
Thresholdin Quiet
Limit of Damage Risk
Threshold of Pain
Speech
Music
Auditory Field
BA 7660-06, 22
Sound
pressure
level, Lp (dB re 20 Pa)
120
100
80
60
40
20
Phon0
1020
3040
50
6070
80
90
100110
120130
20 Hz 100 Hz 1 kHz 10 kHzFrequency
970379
Equal Loudness Contours for Pure Tones
BA 7660-06, 23
Change in Sound Level (dB)
Change in Perceived Loudness
3
5
10
15
20
Just perceptible
Noticeable difference
Twice (or 1/2) as loud
Large change
Four times (or 1/4) as loud
Perception of Noise
BA 7660-06, 24
40
20
0
20 Hz 100 1 kHz 10 kHz
40
0
-20
-40
20 Hz 100 1 kHz 10 kHz
40
Lp (dB)
Lp (dB)
A-weighting
40 dB Equal Loudness Contour normalized to 0 dB at 1kHz
40 dB Equal Loudness Contour inverted and compared with A-weighting
40 dB Equal Loudness Contours and A-Weight
BA 7660-06, 25
0
-20
-40
10 100 1 k 10 k
Lp [dB]
AB
CD AB + C
D
Lin.
Frequency[Hz]
-60
20 k2 k 5 k200 50020 50
Frequency Weighting Curves
BA 7660-06, 26
0
-20
-40
10 100 1 k 10 k
Lp [dB]
A-weighting
Frequency[Hz]
-60
20 k2 k 5 k200 50020 50
L = 8.6dB
Calibration and Weighting!
BA 7660-06, 27
FastSlow
Impulse
87.2
RMSPeak
Weighting
Use of Frequency Weighting
BA 7660-06, 28
FastSlow
Impulse
RMSPeak
87.2
321 n
Serial Analysis
BA 7660-06, 29
FastSlow
Impulse
RMSPeak
87.2
321 n
Parallel Analysis
BA 7660-06, 30
FastSlow
Impulse
87.2
RMSPeak
Weighting1/1, 1/3 oct
125 250 500 1k 2k 4k 8k L A20
40
60
80
100dB 1/3 Octave Analysis
The Sound Level Analyzer
BA 7660-06, 31
L[dB]
Frequency[Hz]
1/1 Octave
1/3 Octave
LA [dB(A)]LB [dB(B)]LC [dB(C)]LD [dB(D)]LLin. [dB]
The Spectrogram and Overall levels
BA 7660-06, 32
Conclusion
Headlines of Basic Frequency Analysis of Sound
Basic introduction to audible frequency range and wavelength of sound
Diffraction, reflection and diffusion of sound Frequency analysis using FFT and Digital filters Fundamental concepts for 1/1 and 1/3 octave filters Human perception of sound and background for A,B,C
and D-weighting Signal flow and analysis in Sound Level Meters
BA 7660-06, 33
Literature for Further Reading
Acoustic Noise Measurements
Brüel & Kjær (BT 0010-12)
Noise Control - Principles and Practice
Brüel & Kjær (188-81)
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