CLIOwin 6.5 PCI User's Manual - Audiomatica Srl

deal with this in more detail later. Here is enough to say that CLIO uses this size also
for the FFT. This is important as the frequency resolution you get is calculated as the
sampling frequency divided by the FFT size. Again for the default settings this is 51200/
16384=3.125Hz. This is already a high resolution. However thinking in terms of octave
or fraction of octave, which are the terms of a logarithmic frequency axis, 3.125Hz is
around 1/2218 of an octave at 10kHz while is around 1/3 of an octave at 10Hz.
Again one example is better than one thousand words. We will measure a twin T notch
filter, probably the most demanding situation for frequency resolution with two sizes,
8k and 64k, and two centre frequency, 10k and 63Hz. Results are in Fig.10.7.
20.0
CLIO
180.0
dBV
Deg
0.0 108.0
-20.0 36.0
-40.0 -36.0
-60.0 -108.0
-80.0 -180.0
20 100 1k Hz
10k 20k
Figure 10.7
Interestingly, the measurements are four but we can see only three curves. In fact the
8k size gives by far enough resolution at 10kHz and the relative curve is completely
hidden by the 64k one. At 63Hz instead the 64k curve, red, differs from the 8k, blue.
We have seen that there is another parameter involved here, which is sampling
frequency. While experimenting with it, we will also make our first impedance
measurement. We will use CLIO internal mode. This is again the default setting, so all
we have to do is to change the Y scale unit to Ohm. We are going to measure a big 15"
professional woofer using 51.2kHz and 6.4kHz leaving size at 16k. The output level is
set at +12dB. Fig.10.8 and 10.9 shows the results.
Chapter 10 - MLS 91