Rohde & Schwarz R&S UPP, Руководство пользователя

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Instrument Functions
R&S
®
UPP
402 User Manual 1411.1055.32 ─ 10
Nth octave analysis is a selective level measurement performed simultaneously in a
number of adjacent frequency bands. The levels of the individual frequency bands are,
however, not measured by narrow bandpass filters as in the case of conventional
octave or third analysis, but instead with the aid of a special high-resolution FFT by
integration of the FFT bins (frequency lines) in the respective band.
The advantage compared to the filter method is the significantly higher frequency reso-
lution, which enables bandwidths down to 1/24th of an octave. The bandwidth of the
subbands is theoretically fully scalable by varying "n" or using frequency tables, such
as the "Critical Bands" defined by means of the Bark scale. The advantage compared
to pure FFT is the logarithmic or user-definable stepping of the frequency range.
Each subband has the relative bandwidth of upper band limit minus lower band limit:
Equation 5-4: Relative bandwidth
Referred to the band center this gives the following results:
●
Octave analysis 70.71 %,
●
Third octave analysis 23.16 %,
●
Sixth octave analysis 11.56 %,
●
Twelfth octave analysis 5.78 %,
●
Twenty-fourth octave analysis 2.89 %,
The reference frequency is 1 kHz. All other band center frequencies are computed by
reference to this frequency by multiplying or dividing by .
Selecting the frequency bands to be measured involves specifying the upper and lower
limit frequencies. A separate RMS value is determined for each selected frequency
band by integrating all the FFT bins in the said band together with the attenuated bins
in the adjacent band. The total RMS value of all the selected frequency bands is
applied to the display of measurement results for the function.
The measurement range of the nth octave analysis starts at a nominal band center fre-
quency of 16 Hz and ends at half the sampling rate or the bandwidth of the analog
analyzer.
The exact, computed frequency bands are used in measurements and for numerical
displays (e.g. with the X value displayed graphically as a cursor or for values displayed
in the "Data List"). The nominal band center frequencies (in line with DIN 323) are
given only for the numerical display of the third and the twelfth octave. Only the octave
frequencies are captioned in the graphical display due to space restrictions.
Frequency Band Analysis