note # 7
in time and frequency domains
performing MLS measures in
noisy environments, a large
part of the background noise (uncorrelated with MLS signal)
but a small part still remains especially when the disturbance
is louder than the MLS.
In these cases an
average of impulse responses may
be useful to increase considerably the Signal/Noise Ratio.
is an example of impulse response measurement:
1 - Impulse response measured in a noisy environment
2 - Same impulse response of figure 1 measured in a noisy environment
in frequency domain may be useful not only to maximize
S/N Ratio, but also to obtain a lower noise floor.
following example plots frequency data from a measurement of
2 tones at 19 kHz and 20 kHz (typically used for evaluating
intermodulation distortion) windowed in the time domain using
a Full Blackman-Harris window. Figure 3 is obtained from a single
measure, figure 4 from an average of 64 cycles. Note that the
noise floor is much lower, when data are averaged!
3 - Frequency data from a single measure
4 - Frequency data from an average of 64 measures
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