#### Zita-Rev1 Delay-Line Filters

In `zita-rev1`, the damping filter for each delay line consists
of a low-shelf filter
[449],^{4.19}in series with a unique first-order lowpass filter that sets
the high-frequency to be half that of the middle-band at a
particular frequency (specified as ``HF Damping'' in the GUI).
Since the filter is constrained to be a lowpass,
for , *i.e.*, the decay time gets
shorter at higher frequencies.

Viewing the resulting damping filter
as a
three-band filter bank (§3.7.5), let and denote the
desired band gains at dc and ``middle frequencies'',
respectively.^{4.20} Then the low shelf may be set for a
desired dc-gain of , and its input (or output) signal
multiplied by to obtain the resulting filter

The lowpass filter is also first order, and to provide half the middle-band at the beginning of the ``high'' band, the lowpass should ``break'' to a gain of at the ``HF Damping'' frequency specified in the GUI. A unity-dc-gain one-pole lowpass has the form [449]

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