Vco - Voltage Controlled Oscillator - Roland SH-1 Instruction Manual

VCO
-
VOLTAGE CONTROLLED OSCILLATOR
6.
PULSE WIDTH
AND
PULSE WIDTH
MODULATION
Puise
width
refers to
the
ratio
of the widths
of the top and
bottom
portions of the pulse
wave. Puise
width
is
measured
in
per-
centages
as
shown
in
the
drawing
at
the
right.
10%
pulse width produces
a
sound
very
rich in
harmonics and
is
often used for
synthesizing sounds such
as
the oboe,
bassoon, and
human
voice.
Note
that a
50%
puise
width
is
nothing
more
than
a
square
wave.
In
addition to using fixed pulse widths,
it
is
possible
to
modulate
the
puise
wave
so
that
the width
of the pulses
varies
con-
tinually,
as
shown
in
the drawing
at the
right.
Using the
LFO
to
modulate
the pulse
width
produces chorus-like sounds.
The
output
of the
envelope generator can
be
used to modulate the
pulse
width to
produce sounds
very
much
like
those of
pizzicato
strings.
With the
PWM MODE
switch at
MANUAL,
this
control allows
manual
adjustment
of
the pulse width.
Note
that
the lowest
position,
50%,
will
produce
a
square wave.
At
the top
is
MIN
(minimum) which
produces
a
pulse
width
of
about 10%.
With the
PWM MODE
switch
set at
LFO
or
ENV-1
,
this slider
controls the depth of the
LFO
or
ENV-1
modulation.
7.
PWM MODE
SWITCH
With
this
switch
at
MANUAL,
the pulse
widths
may
be
set
manually by
means
of
the
PULSE
WIDTH
MOD
slider.
In
LFO,
the pulse
width
will
be
modulated by
the
LFO
output,
and
in
ENV-1, by
the
output
of
ENVELOPE GENERATOR
1.
(1)
PULSE
WIDTH
WAVEFORM
10%
25%
50%
,
—
PULSE WIDTH MOD
PULSE WIDTH
MIN
1
i
to
Imanual
ENV-1
o
AX
(2)
PWM BY LFO
—
PULSE WIDTH
MOD
—
PULSE WIDTH
MSN
A
.
AA
LFO
OUTPUT
WAVEFORM
(3)
PWM BY
ENV-1
ENV-1
SIGNAL
OUTPUT
WAVEFORM
r
ENV-1
—
PULSE WIDTH MOD
—
PULSE WIDTH
min
n
.
. AA
LFO
y
ENV-1
WAVEFORMS AND HARMONICS
All
waveforms except the
sine
wave
can be
generated
by
a
combination
of a
fundamental
sine
wave
of the
pitch
frequency and
a
group of
sine
waves which
are
multiples of the
fundamental; therefore,
any waveform
can be synthesized
by combining
a
fundamental
sine
waveform
with
a
proper
ratio
of harmonics.
The drawing
below shows
a
funda-
mental with
its
harmonics.
The white
notes are
even
numbered harmonics
and the black notes
are
odd num-
bered harmonics. (True
harmonics
are
actually slightly
different
from
the
pitches
produced by the equally
tempered
scale.) Ail
waveforms, except
the
sine
wave,
contain harmonics.
It is
this
harmonic content
that gives
each
sound
its
particular
tone
color.
~e~
8v*V
-e-
i
FUNDAMENTAL 2ND 3RD 4TH 5TH 6TH 7TH
8TH
9TH 10TH
HARMONIC
8' 4* 2-2/3' 2' 1-2/3'
1-1/3"
-
r
8/9'
4/5'
11