45
f
Δ
Freq
Display Line
This real peak is not shown in
graph
Real Spectrum
This points are displayed in
the graph
[Fig. V-2-11] Picket Fence Error
3. FFT Based Octave Analysis
FFT analysis is named narrow band frequency analysis, but octave analysis which is describing in
this paragraph is called broad band analysis. Octave means the twice frequency of reference’s
frequency. Reference frequency is defined as 1kHz in the International Standards-ANSI S1.11.
Therefore, we can make bandpass filters with center frequency which is based on octave of 1kHz.
Octave analysis uses a lot of defined bandpass filter. The 1/1 octave bandpass filter with 1kHz
center frequency is shown in [Fig. V-3-2]. This 1/1 octave filter means bandpass filter with a full
octave band. 1/3 octave filters are realized by bandpass filter with bandwidth that is divided an octave
by 3. Therefore, you can get 1/1 octave data from 1/3 octave data.
[Fig. V-3-1] Concept of Octave
f
c
=1000
f
l
=708
f
u
=1410
Bandwidth
Frequency
L
[Fig. V-3-2] 1/1 Octave Based Bandpass Filter with 1kHz Center Frequency and an octave bandwidth
Содержание SLA-PA201
Страница 64: ...64 Appendix 1 The Theory for calculating RMS by ISO2631 and ISO8041 ...
Страница 67: ...67 Appendix 2 Frequency Response of Filter in the Vibration Level Meter ...
Страница 75: ...75 Appendix 3 Theory of WBCombined Filter and Frequency Response ISO6954 Filter ...
Страница 79: ...79 Fig 2 Lowpass Filter with 100Hz Cutoff Fig 3 a v transition Frequency Response ...
Страница 88: ...88 Fig 12 Error between theoretical value and measured value ...