>@9
Multitone Audio Test System
User Manual
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3.32
Comparability of Multitone Measurements
One has to be aware that the results of multitone testing cannot be compared directly with
conventionally acquired results. For instance, distortion products may appear over the entire
band due to the fact that each signal bin produces harmonics and intermodulates with other
signal bins. The strict separation between harmonic distortion and intermodulation cannot be
guaranteed, since at certain signal bins some intermodulation products and harmonic
frequencies may fall together, thus influencing the Distortion as well as the SINAD results..
However, a multitone signal comes much closer to a "real-world“ signal than any single tone
test signal. The results are in qualitative terms comparable with conventional measurement
results as long as the specific theory behind multitone testing is considered. With a single
tone stimulus, the achieved results are directly comparable to conventional analyzers.
Please refer to the corresponding application note, filed in the appendix of this manual.
Signal Table
>@9
supports five different blocklengths. According to
Equation 3
to
Equation 5
, each
blocklength results in the parameter of
Table 1
. Please observe that the minimum signal bin
frequency is
≥
20Hz and that the overall duration of a burst always is longer than of a block.
Blocklength
Min. Burst Duration
(without Header)
Typical Burst
Duration
Generator
Resolution
Analyzer
Resolution
512
154 ms
260 ms
93.8 Hz
46.9 Hz
1024
284 ms
390 ms
46.9 Hz
23.4 Hz
2048
344 ms
450 ms
23.4 Hz
11.7 Hz
4096
684 ms
790 ms
11.7 Hz
5.9 Hz
8192
854 ms
960 ms
5.9 Hz
2.9 Hz
Table 1 Available Blocklengths
Blocklength 512
Frequency spacing
∆
f 93.75
Hz
Analyzer resolution
46.875 Hz
Bin_Min (f
min
) 1
(93.8
Hz)
Bin_Max (f
max
) 213
(19.969
kHz)
Table 2 Signal Parameter with Blocklength 512 @ f
s
=48kHz
0
0.005
0.01
0.015
0.02
0.025
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
Crestfactor=7.87
Fig. 14 Non-Optimized Multitone Signal
0
0.005
0.01
0.015
0.02
0.025
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
Crestfactor=2.71
Fig. 15 Optimized Multitone Signal
