Soft dB Zen-Ten User guide - Manual (Page 13)

User manual for the ZEN 3-channel X-LMS controller Soft dB inc.
Figure 8 : Autospectrum of a reference signal (control ON and subtraction OFF)
To be able to make an adequate subtraction of the control output contributions, the
primary path control filters must be identified (filters CxRx). To reduce calculation time,
only the direct primary control path filters are used. This relies on the following
hypothesis: the major part of the control output contributions on a specific reference
signal (x) comes from the associated control source (x). In others words, CxRy (where
Y≠X) are negligible.
In most cases, the identification precision of the CxRx filter is not critical. If the distance
between the reference sensor and the control source is small (which is suitable in almost
all cases), a filter with a small length is adequate. In some cases, the control is stable even
if no subtraction is done. Most control systems do not have this feature. But with the ZEN
controller, the user can bypass this feature if the case does not require the subtraction of
the control output contribution.
ZEN User Manual p. 13