The Vocoder Of The Virus - Access VIRUS CLASSIC User Manual

The Vocoder Of The Virus

Although vocoder sounds have seen a comeback in the recent time, many musicians do not
specifically know how they work or even more importantly, how they sound! Various Vocoder
presets are stored In the last section of SINGLE bank D (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 necessarily 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 departure and edit these to
create your own sounds. This means that you don't have to start from scratch and that the Voc-
oder's parameters are set to viable values, which will facilitate programming considerably.
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 signal 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 spectrum. Every bandpass filter is followed by an
envelope follower which uses the level of the signal to create a control signal. This part of the
vocoder is called a modulator bank.
The carrier signal is treated in a similar way. It is split into several bands by a chain of bandbass
filters. Different to the technique used above, the bandpass filters are not followed by envelope
followers. The circuit uses amplifiers which are levelled by the control signal output of the enve-
lope followers of the modulator banks. This part of the vocoder is called the carrier bank or syn-
thesis part.
As soon as the modulator detects a signal in a certain frequency range, its envelope follower
levels the corresponding band in the synthesis part. In other words: Just the frequency band of
the carrier signal (the steady tone), which is a part of the modulator signal (the spoken voice) in
this second, is being passed to the output. This is why the steady tone starts to speak. The
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The Vocoder Of The Virus