Eventide PS101, Инструкция по эксплуатации

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part 2 Instant Phaser Mk II
2.1 The Instant Phaser
Originally released in 1971, the Eventide Clockworks Instant Phaser was designed to
replace the tedious and costly effort required to set up tape flanging. Because, at the
time, the cost of the electronic components required to produce a delay of the neces-
sary length was prohibitively expensive, the Instant Phaser uses a series of electronic
phase shift networks. The phase shift produced by these phase shift networks was elec-
tronically controllable, allowing the user to sweep the nulls produced in the frequency
spectrum in a manner similar to the effect of varying a time delay. Although the effect
of varying these phase shift networks approached that of tape flanging, it wasn’t quite
the same. This technique is now recognized by musicians everywhere as Phasing.
2.2 Phasing
The basis of phasing, both electronically and digitally, is a filter known as the all-pass
filter. As one might assume, this filter is so named because it passes signals of all fre-
quencies, but its output phase varies as a function of frequency. For a single all-pass
section, the maximum phase variation is 180 degrees. By adding the input of the filter
to the output of the filter in a 1:1 ratio, the added signals will be reinforced at frequen-
cies where the phase shift is near zero and cancelled where the phase shift is near 180
degrees.
To produce the desired notches in the output spectrum, several such all-pass filters are
connected in series. For any such phase shift network there will be half as many notches
in the output spectrum as there are all-pass filters. The Eventide Clockworks Instant
Phaser has 8 all-pass filters arranged in pairs, resulting in 4 notches in the output spec-
trum.
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