The Audio Mixer also contains aslider controlling
the amount of input accepted from any electronic
instrument signal inserted into the External Audio In
jack on the back panel of the SH-09. The SH-09
12
may be used in several different ways to process
external instruments (in contrast to processing its
own VCO signal), and these are discussed in this
manuals Interfacing section.
Voltage Controlled
Filter
The basic VCO sound now passes automatically
from the Audio Mixer on through the Voltage Con-
trolled Filter (VCF). Here the tone resulting from
choices made within the VCO and Audio Mixer
may be finely adjusted and manipulated.
The basic patch passes the VCO sound directly
through the VCF unchanged, opened by raising the
Cutoff Frequency slider fully. An understanding of
the effect of the filter Cutoff is basic to an unders-
tanding of the entire VCF section.
The SH-09 VCF is ahigh quality Low Pass Filter.
With the Filter Cutoff slider set at '10', it has no
effect on the sound. As this slider is lowered, the
tone becomes progressively more mellow as the
higher parts of the tone are removed, becoming a
pure sine tone just before it is filtered away to
silence. Lower and raise this slider at different
speeds using each basic waveform from the VCO
to obtain an aural picture of the various colors
available and also of the effect of motion within the
filter.
Motion within the filter, changing the tone during
musical notes, is critical to many synthesizer
sounds. Some synthesized sounds are based on a
'passive' filter, afixed Cutoff Frequency setting with
no motion or change in tone. Others depend on the
tone changing 'actively' during the length of each
note, either arepeating change controlled by the
LFO Modulator or asingle sweep initiated by the
Envelope control. The most basic demonstration
would be to compare the basic brass and string
patches presented in this manuals section on
Patches. The prime difference between these two
sounds is the 'passive' filter of the string patch as
contrasted to the 'active' filter of the brass patch.
Move the Cutoff Frequency slider to '1 0' while its
selector is in the middle, ENV (positive envelope),
positioa Press any key and the note will change
both in volume and tone according to the shape
set in the ENV section of our basic patch, getting
brighter and louder, then more mellow and soft
The volume level followes the tone just as it did
when the slider was manually moved. This experi-
ment moves the filter exactly the way it could be
done manually, but with more potential speed, pre-
cision and ease through automatic control. Repeat
this procedure with different waveforms and
different amounts of VCF Envelope Control.
Return the Cutoff Frequency slider to '10', move the
selector to EMV (inverted envelope) and
move the VCF Envelope Control to '6'. Your effect
is now reversed, closing the filter rather than open-
ing it moving this time from bright and loud to
mellow and less loud and back again each time a
key is pressed. This inverted envelope is very use-
ful in creating plucked or strong, punching syn-
thesizer sounds with lots of dynamic motion.
Experiment here with different waveforms and
different Cutoff Frequency starting points and
amounts of Envelope Modulation. Patches are
given later for specific applications of this feature.
The ENV FOL'R position on the three position VCF
Envelope Mode Selector uses the natural shape of
notes introduced at the External Audio In to move
the filter, allowing instruments such as electric
piano or electric guitar with no Gate Voltage out-
puts to drive the SH-09. Specifics on this pro-
cedure are given in the Interfacing section of this
manual.
The MOD slider within the VCF section allows you
to change the tone of your note with the IFO
Modulator. Begin with your basic patch, lower the
Cutoff Frequency slightly to 7', and gradually raise
the MOD slider. You will hear atone/volume tre-
molo (the speed and shape are determined again
in the Modulator section), the depth of tremolo
varying with the MOD slider position. It is useful to
note here that the tremolo is smoothly, alternately
both raising and lowering the Cutoff Frequency (for
brighter and more mellow tone, respectively). For
this reason the Cutoff Frequency slider has been
lowered slightly to make room for both actions. If
the Cutoff Frequency slider was in either extreme
position, any tremolo would lose its smoothness as
only half of its cycle could have any influence on
what is heard. Experiment with this now and later
check the Vibraphone patch for aspecific exam-
ple.
The Resonance slider in the VCF section emphas-
izes the tone at the precise edge of the Cutoff Fre-
quency. Place the Cutoff Frequency slider at any
point that allows atone to pass, then add any-
where from '0' to '6' of the Resonance slider and
you will hear aslight difference in tone. Leave the
Resonance slider at '6' and move the Cutoff Fre-
quency slider. Resonance emphasizes the edge of
the Cutoff and when it is moved the motion is
emphasized. The prime use of Resonance is to
emphasize tone in motion, such as the twang of
the bass guitar in the Shuffle Bass patch given
later in this manual. You may wish to leave the
Resonance slider at '6' or less and repeat the
experiments with Envelope or LFO Modulation of
the VCF to learn how these automatic changes in
tone are emphasized using Resonance.
Once that is completed, push the Resonance slider
fully to '10', and again move the Cutoff Frequency
slider. You will now hear an extra pitch in addition
to that produced by the VCO, one whose pitch is
determined by the VCF Cutoff point Silence the
VCO at the Audio Mixer and experiment with
various kinds of modulation using the Resonance
as an extra oscillator —all functions which altered
the tone using the VCF will now move the pitch of
the VCF produced note in the same manner. This
use of the Resonance as an extra oscillator may be