User`s manual

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size 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 48000/16384=2.929 Hz. This is already a high resolution. However thinking
in terms of octave or fractions of an octave, which are the terms of a logarithmic
frequency axis, 2.929Hz is around 1/2218 of an octave at 10kHz while is around
1/3 of an octave at 10Hz.
Again an example is better than a 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 center frequencies, 10k and 63Hz. Results are in
Fig.10.7.
Audiomatica Srl MLS - Frequency Response 06/07/2001 15.02.28
CH A dBV Unsmoothed 51.2kHz 65K Rectangular File: fig3a.mls
100 1k 10k 20k20 Hz
20.0
dBV
180.0
Deg
0.0 108.0
-20.0 36.0
-40.0 -36.0
-60.0 -108.0
-80.0 -180.0
CL IO
Figure 10.7
Interestingly, while we took four measurements we can only effectively see three
curves. In actual fact the 8k size gives by far enough resolution at 10kHz and the
associated curve is completely hidden by the 64k one. The 64k curve (Red) only
differs from the 8k curve (blue) at 63Hz.
10 MLS & LOG CHIRP 121