\.
CONTROLLE
D
VCO
PITCH
=
FREQUENCY
VCF
TONE
COLOR
=
HARMONIC
CONTENT
VCA
LOUDNESS
*
AMPLITUDE
CONTROLLER
\
KEYBOARD
The most
common
use
of the key-
board control
voltage
is
for the
control
of
the pitch of a VCO; the
pitch produced will correspond
to
the key pressed.
The
tone color of most
instruments
will vary with pitch; higher pitches
often produce
brighter
tone
colors,
lower pitches darker tone
colors.
For this purpose, the VCF
can
be
controlled
by
the keyboard.
The control of loudness
by
means
of
the keyboard is of little practical use;
the
SH-1
has
no
provision for this
type
of
control.
ENVELOPE
With some sounds, it is
desirable
to
incorporate
pitch changes during
the
production of each note.
The
SH-1
contains a
special envelope
generator (autobend) provided
exclu-
sively for this purpose.
The tone color of many
instruments,
particularly the wind instruments,
changes during the production of
each
note.
This effect can
be
produced
with envelope generator control of
the VCF.
Raising the VCF
RESO-
NANCE
control will produce sounds
possible only on
the synthesizer.
The loudness pattern
(or articulation)
of
a
sound is produced
by
using
the
output
of the envelope generator to
control the VCA.
LFO
(MODULATOR)
The LFO (Low
Frequency Oscilla-
tor) produces low
frequency wave
forms. Using the LFO
sine wave out-
put to
control the
pitch of the VCO
will produce vibrato
effects. The LFO
square wave output
will produce
trills.
With some sounds, the tone color
will vary
at
the same rate as
vibrato.
This can be done with LFO
control
of
the
VCF.
Raising the VCF
RESO-
NANCE
control will produce "growl"
effects.
The
SH-1 does not provide
for LFO
control of the
VCA;
however, the
square wave
output
of the LFO
can
be used for triggering
the
envelope
generators to produce rapidly repeat-
ing
notes.
BASIC SYNTHESIZER
THEORY
In the
synthesizer, then, the
three qualities
of
sound
are
controlled by the
VCO (pitch),
VCF (tone color), and
VCA (loudness).
The
tremendous
versatility of the
synthesizer is due
to
the
principle of voltage control. The
above
table
shows some of the
possibilities.
The keyboard
has
two
outputs: a control voltage
and
a
gate pulse. The
level of the control voltage
will correspond to
the last key pressed.
The
control voltage output
is most often
used
to
control
the frequency of the VCO, thus,
when
8 key
is pressed, the VCO
will produce
the
pitch
which
is related to
that key. The key-
board produces a
gate pulse each time a key
is
pressed. The
gate pulse is most often
used to
trigger the envelope
generator into operation.
The
control voltage output
of the envelope
generator, then, "opens"
the VCA
to
let
the
sound wave out, thus the
synthesizer
produces
sound each time a key
is depressed.
The
shape of the envelope is controlled by
the
envelope
generator sliders. When the
sliders are
set, the
envelope generator will generate a
con-
trol voltage which
corresponds
to
the shape
of
the desired envelope.
When this control
voltage
controls the VCA, it
regulates the loudness
level
of the
sound
so
that the
loudness will rise
and
fall in
the desired
pattern.
Fig.
4 shows
the
output
sound
wave when the
envelope generator
controls are set to
produce a
violin-like envelope,
and
Fig.
5
shows the output
sound for
a
piano-
or
guitar-like envelope.
The tone
color of many
types of sound
will
often change during
the production
of each
note.
This can be
done with the
synthesizer
by
using the output
of the
envelope generator to
control
the VCF.
There
are two other
sources of control voltage:
the
LFO
(Low Frequency
Oscillator)
and the
S/H
(Sample and Hold),
each of which can be
used to
control various
synthesizer functions.
In
the
following pages, the
functions of each
of
the
synthesizer elements is
explained in detail.
When trying
various sounds, try to
analyze
exactly
what is happening;
this will give you
a
better
understanding of thesynthesizer.
Synthe-
sizer sounds
are very much enhanced by
the use
of
effects units
such as echo chambers,
re-
verberators, chorus
effects, phase
shifters,
flangers,
etc,
thus
their
use
is highly
recom-
mended.
FIG.
4
-VIOLIN-LIKE SOUND
FIG.
5
-PIANO-LIKE
SOUND
FIG.
6
-
PARTS
OF
ENVELOPE
-A*|*»D-
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