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ACCESS VIRUS OS4

Envelope Follower

This function of the Virus is a spe-
cial delicacy. It really upgrades the 
process of filtering (or any other 
processing) of an external audio 
signal. What we have here is a so 
called Envelope Follower that can 
evaluate the volume envelope of 
an external audio signal with a 
selectable speed or inertia and 
then creates an appropriate modu-
lation signal. This signal can be 
used to control any Virus parame-
ter via the Modulation Matrix. In 
UNISON Mode the Envelope Fol-
lower works in true stereo, you can 
find the parameters in the effects 
menu under INPUT. One example 
for its application: A drumloop 
serves as the external signal; the 
Envelope Follower controls the fil-
ters cutoff frequency and creates a 
typical "Autowah" effect, whereby 
the filter is opened according to 
the drumloop's volume (respec-
tively its beats). In addition to this, 
or as an alternative, you can con-
trol other parameters. Of course 
you can also use the external sig-
nal as the modulation source with-
out processing it in the Virus at all.

When the Envelope Follower is 
activated it replaces the filter 
envelope, so that when Env 
Amount is turned up, it directly 
affects the filter frequencies. Any 
other parameter can be modulated 
with the Envelope Follower via the 
Modulation Matrix (ASSIGN). 
Select FiltEnv as the modulation 
source

Three filter envelope knobs are 
used to control the envelope fol-
lower when it is active:

Knob: FILTER ATTACK  It controls 
the attack rate of the envelope fol-
lower. With this parameter, you 
can determine how fast the enve-
lope follower will respond to the 
rise in signal level. Higher values 
slow the envelope follower down 
and delay its response.