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CHAPTER 

21

The Vocoder of the VIRUS

Although vocoder sounds have 
seen a comeback in the recent 
time, many musicians do not spe-
cifically know how they work or 
even more importantly, how they 
sound! Various Vocoder presets are 
stored In the last section of SINGLE 
bank B (grammalogue ”VOC”). 
These SINGLEs require an audio 
signal being fed to the external 
inputs. The keyboard also needs to 
be played on most of the presets. 
The Virus Vocoder is not necessar-
ily easy to handle. You should 
always refer to an existing Vocoder 
preset for editing.

The Vocoder is one of the most 
complex sections of the Virus. For 
this reason, we recommend that 
you use factory sounds that use 
the Vocoder as your point of depar-
ture and edit these to create your 
own sounds. This means that you 
don’t have to start from scratch 
and that the Vocoder’s parameters 
are set to viable values, which will 
facilitate programming consider-
ably.

A Vocoder creates a new sound by 
combining two signals. The timbre 
of the so called analysis signal (or 
modulator signal) forms the carrier 
signal. A typical example for a 
modulator signal is the human 
voice, another suitable carrier sig-
nal can be a steady tone with rich 
harmonics.

The sound characteristic is being 
rendered into the new sound by 
two cascades of bandpass filters: 
The modulator signal is being send 
through several parallel bandpass 
filters, which only pass through a 
certain part of the whole spec-
trum. Every bandpass filter is fol-
lowed by an envelope follower 
which uses the level of the signal 
to create a control signal. This part 
of the vocoder is called a modula-
tor bank. 

The carrier signal is treated in a 
similar way. It is split into several 
bands by a chain of bandbass fil-
ters. Different to the technique 
used above, the bandpass filters 
are not followed by envelope fol-
lowers. The circuit uses amplifiers 
which are levelled by the control 
signal output of the envelope fol-