CLIOwin 6.5 PCI User's Manual - Audiomatica Srl

9.5 AVERAGING
Averaging plays a very important role in FFT and RTA analysis. It is vital when analyzing
signals buried with noise. It is also important when taking spatially averaged measurements.
CLIOwin has flexible averaging capabilities. Averaging basically means adding
and dividing for the number of additions made. To start an averaged FFT measurement
you need to set a number bigger than one in the Target Average drop down; otherwise
you have a continuously refreshing single measurement that will continue until the Stop
button is pressed. It is possible to choose between linear and exponential averaging.
The instrument behaves differently in the two averaging modes. In linear averaging the
measurement is continued until the target is reached, then it automatically stops. What
you got is exactly what we just explained. In exponential averaging the measurement
never stops. When the target is reached the averaging continues relying on a
mathematical formula which discards the oldest acquisitions and gives more and more
importance to newer ones. The exponential averaging is the default one.
As an example Fig. 9.4 compares a single 1kHz sinusoid FFT analysis and 100 averages
one.
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0.00 2000 4000 6000 8000 10000 12000 14000 16000 Hz 18000 20000 0.00 2000 4000 6000 8000 10000 12000 14000 16000 Hz 18000 20000
Figure 9.4
This is a classical example of signal buried with noise: the sinusoid's 9th harmonic is
clearly visible after 100 averages, but invisible for a single acquisition.
Another important feature, when averaging, is the possibility of continuing averaging
after a measurement is stopped, has reached its target or a previous measurement has
been loaded from disk. CLIOwin has this capability when selecting continue in the drop
down menu available aside the Go button (Fig.9.5).
Figure 9.5
Selecting the continue option allows, as an example, for spatially averaged measurements.
Fig. 9.6 shows two 1/3 octave RTA measurements of a small HT satellite at
listening position: the black one is a single 10 averages measurement taken on axis;
the red one is, instead, built, using the continue option, adding a total of eleven 10
averages measurements taken moving from -25 degrees left to +25 right of the speaker
itself.
82 Chapter 9 - FFT