User`s manual

12.4 MAKING A CUMULATIVE SPECTRAL DECAY
A cumulative spectral decay starts loading an impulse response from disk. Suppose
we have taken an anechoic response of a medium sized two ways loudspeaker; the
impulse response is shown in Fig.12.3.
Let's first select a reflection free part of it. By selecting the start and stop window
points we obtain the first two information parameters required for the waterfall
facility: zero time will be referenced to the start of the start window, while the Z
axis will provide the measurement range between the stop and start window points
(unless a Time Shift is chosen).
Figure 12.3
Going inside the Waterfall Settings dialog we decide to view our measurement
between 150 and 20000Hz, then apply 1/12 octave smoothing. We are now ready
for a waterfall!
Figure 12.4
The Go button is enabled. Press it, you should obtain a waterfall like the one in the
left part Fig. 12.5. Press now the Color Scale button followed by the Interpolate
Colors buttons, now you should have the color map shown in the right part of Fig.
12.5. The two representations are not exclusive, they mutually complement each
other; you will gain experience understanding all the subtle details of a waterfall
processing and how they are represented either in the 3D or in the color map. For
example the color map represents better the frequency of decaying modes as they
result as straight color patterns parallel to the time axis; the 3D waterfall is more
familiar when you look at zero time frequency plot and try to visualize how it
modifies during decay.
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