Reed Ghazala, author of this article, wrote an extensive series of articles for the Experimental Musical Instruments quarterly journal between 1993 and 1999. For a fuller exposition of his circuit-bending techniques, you can find the last of this series, published in EMI in June 1999, posted on the Oddmusic web site.
This article appeared in Experimental Musical Instruments Volume 12 #2, December 1996. The print version of the article contains several photos and an additional sidebar not contained in this version appearing on the World Wide Web.
Copyright 1996, Q.R. Ghazala..
The Casio SK-1: Escapist Sample Shuttle
By Q.R. Ghazala
The glass in my workshop window is 70 years old. Its thickness varies, and the world
outside passes by in fluid, undulating waves. In the cracks of this glass, where a
forgotten autumn's chore may have left its mark, can be seen all the colors of the
rainbow, refracted splendidly for anyone given to close inspection. Glued to a rippled
pane, a fine rubber skink watches a small cricket climb up the yellowed edge of an old
skyharp postcard. Through the Victorian crystal teardrops and hanging stained glass
spheres, through the pinned-up templates and photos and chipped green paint of the
window's dusty sash flows the orange evening sunlight, wavy after passing through the
magic window-lens. A breeze comes now and gently swings the antique glass balls, their
projected optical flares rocking back and forth upon circuit drawings, colored-light
fairies on a rippled orange sea.
The plans, today, upon which the fairies dance are those of the circuit-bent Casio SK-1.
("Circuit-bending" refers to the process of creative short-circuiting by which
standard audio electronics are radically modified to produce unique experimental
instruments. A further description of these techniques can be read in EMI Volume VIII #1,
1992.) Readers of this article series have inquired over the years about the viability of
keyboard instruments as a focus for circuit-bending. While I'm inclined to think the end
result of the bending process is often better suited to less linear sound machines,
keyboards were an early target of mine, and the circuit-bent SK-1 is an exceptional
example of deep-end anti-theory application combined with equal-tempered polyphony.
Abstract sound fields thick and intriguing, complex voices, split keyboards, strange tone
shaping and extended ADSR envelopes begin the list of new possibilities... but more on
such things in a moment.
Casio's SK-1 introduced digital sampling to more individuals than any other sampler to
date. The SK-1 began to appear on store shelves in 1986. For its time, at its price and
with its functions, there was nothing else like it. Main features of this 32-note mid-size
keyboard include:
- | 4-note polyphony, available live and also in memory for digital
record/playback functions of two types: 1) real-time 4-note polyphony, and 2) 3-channel
multi-track memory coupled with a "one key play" system allowing notes in memory
to be manually sequenced for editing purposes; |
- | 5 PCM voices, 1 user-sampled voice, 3 harmonic synthesis voices and one
user-adjustable harmonic synthesis voice (this nice feature provides a tone in which most
of the first 16 harmonics are present and can be adjusted in strength, with up to 14
levels of accentuation for each);* |
- | Thirteen different preset ADSR envelopes which can be applied to any
voice in use;* |
- | Preset portamento and vibrato effects; |
- | 8 bit PCM sampling at 9.38 kHz (sample time is approximately 1.4
seconds); |
- | Built-in condenser microphone for inputting samples, as well as two input
jacks line and external microphone; |
- | Line-output; |
- | Master tuning; |
- | 11 auto rhythms with chord accompaniment; |
... and lastly, that button everyone dreads hitting by accident... the
Demo Tune (which circuit-bending reconstructs in a wonderfully irresponsible manner). |
|
*PCM (Pulse Code Modulation) is a high-quality means of digital audio data processing. ASDR (Attack-Decay-Sustain-Release) describes the four main parameters of sound envelope transients as commonly addressed in electronic synthesis techniques. |
No, it's not a hi-fi sampler. But thousands of people found the SK-1's audio quality good
enough to keep interest on high for some time.
Plenty of SK-1s are still around today, patiently waiting to be reborn through
circuit-bending. Since the resultant instrument is so exotic in its behavior, so
intriguing in its sounds and so attainable through standard rewiring techniques, I'll
devote this column to the SK-1's anti-theory transformation.
My first SK-1 was bought during its heyday at a price of around $90. I quickly made two
modifications and, until lately, thought no further about altering it. These early changes
resulted in two jacks being mounted on the SK-1's case. One was wired so that it would
accept a remote sampling trigger to use in conjunction with an external microphone. The
other jack was wired to accept programmed voltage pulses (such as those generated by drum
machines) so as to trigger the "one key play" function thereby turning the
SK-1's note memory into a nicely controlled sequencer. Push "start" on the drum
machine and both it and the SK-1 perform in tight synch. Fun.
Years pass... the SK-1 is overshadowed by industry changes and pushed to the back of the
shelf (go take out those batteries!). Few things tend to encourage a circuit-bending
experiment more than finding a promising target device at a bargain price. Especially if
the device is a duplicate of an item you already own and care for, and is one you'd like
to bend but are hesitant for fear of damaging it in the process. So I was thrilled to
recently find a SK-1 (with a key missing) for only $1.50 at a thrift shop. Oddly, several
days later I found another SK-1, this time in great shape and costing $5.00 at a different
second-hand shop. The one with the missing key became my prototype, the $5.00 unit became
the finished instrument and my original SK-1 remains as it was before.
Following the usual process of circuit-bending, the instrument was expanded upon to the
degree of now providing 28 new controls (switches, dials and body-contacts), 7 micro green
& red LED logic pilots and an ultra-bright sound envelope LED... 36 modifications.
With all the added controls turned off, the SK-1 operates as normal. The modifications are
easy to find and are open to anyone familiar with the use of a soldering pencil (small,
low-wattage soldering iron).
Once again, the creative short-circuit is on the loose, the repercussions of its catalytic
anti-theory wreaking indeterminate digital havoc within the all-too-proper halls of
previously strict program logic. The new controls were discovered one of two ways. Either
by listening to the instrument's voices while 1) using a wire to momentarily connect
arbitrary circuit board points to each other (this giving rise to 20 of the 22
circuit-bending switches, their purpose being to implement and combine the creative
short-circuits just found), or 2) using fingertips to connect arbitrary circuit points to
each other (the 3 body-contacts and 2 of the 3 dials [potentiometers or pots, variable
resistors] were found in such a way).
This last activity, touching an active circuit-board with the fingers to hear what changes
occur in the sound, should be done only with low-voltage, battery-powered circuitry.
Circuits containing large capacitors or step-up transformers are to be avoided. These are
simple to recognize; check out a beginner's electronic Project book if unfamiliar. These
components usually appear in various types of lighting circuits, practically never in the
audio electronics appropriate for circuit-bending. At any rate, the idea is that
interesting sounds arising from finger contact can be hard-wired into existence by
soldering a pot (variable resistor) between the two points so discovered. The middle
solder lug of the pot is wired to one circuit point, an outside lug of the pot to the
other circuit point. After all, that's exactly what your body is doing in the same
situation. As the electrical energy is conducted through your flesh its potential changes
as you vary the resistance presented it by adjusting the pressure of your fingertips on
the circuit-board. You've become, in essence, a variable human resistor (aren't we all?).
Conductivity will differ from individual to individual, so there is no exact
recommendation I can give as to the resistance rating of the pot. Experiments with a 500K
will provide a good starting point.
My SK-1 circuit-bending applications fell into 9 sections. These are the IMAGE GROUP of 9
switches, the SKEW GROUP of 7 switches + 1 pot, the BODY CONTACT GROUP of 3 brass spheres,
the PITCH control dial, the POLY control dial, the AXIS GROUP of 3 switches, the RESET
GROUP of 2 switches, the LOGIC PILOTS GROUP of 7 LEDs + on/off switch and, lastly, the
SOUND ENVELOPE LED. None of these expansions of the SK-1 were hard to find. Following are
brief explanations of these new circuit-bending discoveries, as well as guidelines for
implementing the changes yourself.
TWO NOTES OF CAUTION
1) Though it seems I haven't harmed any normal functions of my 3 SK-1s, there's no
guarantee that a connection I didn't try exists that could damage or destroy the circuit.
In the same vein, manufacturer's design changes can create a situation in which a
previously trusted circuit-bending connection becomes either inoperative or destructive on
a later model. Therefore, while my instructions are valid in pertaining to my SK-1s, they
may not be advisable for yours.
2) The bending procedure requires a great deal of soldering tiny wires to very closely
spaced IC pins protruding through the underside of the board. Very careful connections
need to be made in order to avoid creating solder bridges between the pins. Quick
connections are also a good idea so as not to overheat the internal IC electronics
connected to the pin. I use a 30-watt grounded soldering station with long, tapered,
1/16" wide chisel-tip on the soldering pencil. For point-to-point connections I use
insulated bought-in-quantity 30-gauge "wire-wrap" wire, the wilder color the
better, and lead-free silver electronic solder.
IMPLEMENTATION AND BEHAVIOR
OF THE CIRCUIT-BENDING EFFECT GROUPS
[Note for web-site readers: while the descriptions that follow will stand on their own,
the photo of the circuit-bent SK-1 that accompanies the print version of this article (EMI
Volume 12 #2) will help in orienting the reader. The photo contains small lettering which
would not reproduce legibly on the screen.]
For persons interested in experimenting on their own SK-1s, my descriptions below assume
the working orientation of circuit is such that the underside of the board faces the
experimenter and that the parallel grouping of three large (28 pin) ICs is to the bottom
left (on reverse of board). In this position a medium-sized electrolytic capacitor is
situated at the top right corner of the circuit-board. This needs to be relocated
elsewhere within the case (on insulated wire extensions) to open up room behind it for new
controls to be mounted.
Image Group
These 9 switches to the right of the keyboard are interconnected between various pins on
the furthest to the left of the three ICs mentioned earlier. Experiment to find these
connections and others. Turning these switches on singly or in combination will create up
to 8-step sound envelopes, up to five keyboard split points (different sounds assigned to
various key groups), oddly evolving tone clusters and extended decays lasting up to 30
seconds or more. The multi-step sound envelopes may combine voices from the SK-1's menu or
create new voices, changing voices, strung end-to-end and finally settling upon an unusual
sustained tone, or slowly fading away. Additionally, choosing a different voice from the
menu may completely change the effect of a given IMAGE switch.
Skew Group
These seven switches and 10K pot make connections between various pins of the same large
IC and a common point on the bottom right-hand side of the board, that being to a pin on
the 14-pin chip just to the left of a board mounting screw. Again, experiment.
Essentially, the five main SKEW switches connect five pins of the large IC to the smaller
IC by running through one of the other two smaller switches in the group. This signal also
passes through the 10K pot. The pot adjusts the strength of the signal passing between the
two chips, and the smaller push-button and toggle switches allow the choice of either
intermittent or continual use of the chosen SKEW effect while playing. So if, say, SKEW
switch 1 is turned on, a connection is made between a pin on the large IC and the pin on
the smaller one. The intensity of the effect is governed with the SKEW pot, and the
musician controls the duration of the effect with the two miniature actuation switches.
The SKEW effects are similar to the IMAGE effects with the addition of adding pulsings to
final voice segments of multi-step sound envelopes. Assorted sustains, echoes, repeats,
doublings, choruses and harmonic distortions also arise from the SKEW effect group.
Body Contact Group
These three brass balls are wired to three circuit traces just to the left of the master
tuning trim pot soldered into position in the center of the board. Primarily pitch
controls, bridging with a fingertip the gap between the center sphere and the one to its
left will lower the frequency. Bridging the gap between center and right will raise the
frequency. Actually, just touching either outside sphere will bend the frequency, but not
as dramatically as when bridging the gaps as mentioned. Very nice real-time vibrato and
pitch-bend are possible in this way. Beyond this application, a moistened fingertip
pressed across all three contacts will bring on an assortment of deep-end audio
calisthenics simply impossible to describe! Tech Note: On a crowded circuit board it can
be hard to tell just which traces your fingers are touching to create the audio changes
heard during this process of exploration. Holding a metal jeweler's screwdriver in each
hand will allow you to touch obvious and specific traces on the board. Electricity will
flow into one screwdriver, through your body and out the other screwdriver back into the
circuit. Varying hand pressure on the screwdrivers will allow you to observe the effect of
changing resistance between the two potential body-contact points.
Pitch Dial
This is simply a 500K pot wired between the two outside body contacts. Decreasing the
resistance raises the overall pitch of the instrument.
Poly Dial
Another 500K pot, this one is connected between the right-hand lug of the SK-1's on-board
master tuning trim pot and any of a number of potential traces on the board. Try traces an
inch or so below center mounting screw. When the resistance is decreased, a note or two of
the polyphony will slowly fade out. This control is used to adjust the degree of
polyphony, especially valuable when applied to the dense abstract sound fields generated
through other circuit-bending controls.
Axis Group
These three switches connect a pin on the large left-hand 28-pin chip (again) to three
pins on the two 28-pin chips to its right. Many possibilities here... experiment! Drastic
voice changing in the form of distant ethereal sounds, rich tonal swells, seemingly chance
music cycles, metallic percussive bursts and endless de-tuned sustains are a few of the
effects created by the AXIS GROUP.
Reset Group
These two switches represent a choice of "HARD RESET" or "SOFT RESET".
As I've stated before, the unusual anti-theory design system of circuit-bending can create
digital exasperation in logic routines, otherwise known as program crash. When the
circuit-bent SK-1 crashes (and it will), four reset options are available. Casio's front
panel "RESET" button might work. If not, turning the SK-1's main power switch
off and back on might work. If both of these fail, my "SOFT RESET" miniature
push-button on the left side of the case could solve the problem. This makes the same
connection as IMAGE switch 2. During initial prototyping I noticed that this connection
could reset certain crashes without powering-down the unit. Yes, I could just flip IMAGE
switch 2 on and back off, but the mini push-button is easier, quicker, and more out of the
way while playing. The "HARD RESET" is a "push-on/push-off" switch
situated next to the mini switch just mentioned. This is the deep crash remedy since it
completely breaks the circuit between the power supply and the board. Therefore, it is
also a MASTER POWER switch. This is the standard reset I include on many circuit-bent
instruments prone to crash. Can you keep a secret? It does the same thing as the tiny
reset switch you're instructed to push with a pencil tip in case of malfunction of your
calculator, answering machine, musical keyboard and lots of other digital whatevers. Yep,
the Big Guys' theory-true toys crash deep enough all by themselves to need as drastic a
thing as battery disconnection to set them straight again too!
Logic Pilot Group
This group of seven miniature red or green LEDs is implemented by connecting the anodes (+
leads) of the LEDs to various pins of the large right-hand 28-pin chip. All LED cathodes
(- leads) then connect through a LOGIC PILOTS power switch (on back of case) to the
negative side of the power supply. The switch to turn them off is needed for two reasons.
First, if left on they continue to drain power unless my added master power switch (HARD
RESET) is turned off. Second, certain IMAGE switches overdrive the LEDs when turned on,
risking eventual burnout. These LEDs flash mysteriously as logic levels (voltages) go high
or low as the instrument functions. These can also be considered STATUS LEDs, and can be
quite informative when gotten used to on this and other circuit-bent instruments. I've
drilled holes for these along the top of the SK-1's case with a few also mounted below,
amidst the control buttons. Circuit connections for these are discovered the same way as
switch connections. Simply use LEDs with alligator clip test lead extensions in place of
the usual short-circuit exploration wire. Remember that LEDs are polarized semiconductors:
if an LED won't light, try reversing its leads and reconnecting it to the circuit. If an
LED glows too brightly or gets hot, try connecting a resistor (experiment around 100 ohm)
between the LED's anode and the circuit.
Sound Envelop LED
This clear, bright, red LED (2,000 mcd) is connected across the speaker terminals and
fluctuates with the intensity of the sound without disturbing sound volume or clarity
(which is not always the case with this parallel wiring scheme). LEDs can also be
connected in series with a speaker if more energy is needed to drive them. Sound envelope
LED connection points can also be found by attaching one LED lead to a speaker terminal
and then touching an extension of the other LED lead to various parts of the active
circuit. In fact, such envelope LEDs can be driven by points discovered on the board
having no direct connection to the speaker whatsoever.
As noted before, circuit-bending the SK-1 does require a good deal of careful work since
tolerances of both soldering and component placement are tight. Much more is possible than
what I've done. Still, a person might want to add, say, only a body-contact and leave the
rest of the SK-1 untouched.
Any newly bent instrument presenting significant sound forms deserves a visual
transformation as well. Once the holes were drilled to accept the new switches, pots, LEDs
and body-contacts, I painted the case of my circuit-bent SK-1 a hi-gloss fire engine red.
Over that went a flat black crackle coat. This is a type of paint that contracts and
cracks apart as it dries, leaving an organic-looking and somewhat fractalized pattern.
From far above the case a sweep in the air of holographic micro glitter (several specks
could fit in the dot of this letter i) was rained down onto the housing, falling like a
star field across the scarlet veins in the black crackle field. These tiny particles
reflect a brilliant spectrum of light, shifting hue in unison as viewing angles change.
A high-solids clear gloss final coating was then applied. This deepens colors, serves as a
sealant and provides a surface upon which an extra-fine-tip opaque paint marker can be
used to label the new controls, and re-label the old, their having been painted over in
the refinishing process. New controls are then mounted, unit is reassembled and wiring is
begun. With the SK-1 I decided not to refinish either the case bottom or the strip above
the keys that contains envelope symbols.
Be forewarned that if you decide to dismantle the entire device to refinish the case as
I've done, the keyboard "trees" need special handling. All the keys, in separate
sets for white and black, are connected to a common tree and remove as single units. It is
the junction of key-to-tree that is very fragile and must be handled with real care. It
takes little force to bend a key out of alignment or snap it off completely.
Exploring the SK-1 circuit is fascinating. In the EFFECT GROUP discussions above I've only
begun to describe the major effects available within the separate groupings. Not only can
each group be depended upon to produce many more effects than those covered, when
multi-group combinations are experimented with (e.g. IMAGE switches 1,3,7 + SKEW switches
2,3 + AXIS switch 1 while touching body-contacts or sweeping POLY dial), the surprising
nature of circuit-bending's ability to always generate new audio behavior becomes evident.
My initial examination of such switching combinations produced 30 strong variations using
the PIANO voice alone.
On some deep-end settings the circuit-bent SK-1 becomes an aleatoric music box, evoking
outlandish chance compositions. Other settings turn the keyboard into an alien sound field
generator, intercombining curtains of relatively pitch-free noises. Peculiar mixtures of
countless types emerge as one moves deeper into switching possibilities... and I now find
myself in the position again of trying to describe the eccentric, many-nuanced voices of
circuit-bending. Like trying to define a rare flavor or shifting color.
As it often is with circuit-bending, these more extreme settings impose a
control/non-control balance that can take some getting used to. Program crash is often
inevitable under these conditions. Charting patch settings and sequences goes a long way
to establish reliable interactions, but the temptation to go a step further and see what
happens is always there. I accept, even enjoy the non-control aspects of circuit-bending,
feeling that they add to the mystery, and knowing that they are an integral part of the
whole fascinating process that I've grown to enjoy so much. I'm reminded of the orange
evening light through my wavy glass, and the prismatic fairy-flares dancing along its
crests upon my SK-1 plans as I sat down to begin writing this article.
I'll admit I thought for a moment of turning on the overhead drawing lamp, chasing the
light fairies away so I could better see my notes. But you know, I didn't.
Reed Ghazala can be reached at :
E-mail: | Anti-Theory POB 20181 Cincinnati, OH 45220 |
|
Reed's full-color Anti-Theory Workshop catalog is now available. A visual treat itself, the 8-panel brochure depicts 19 different instruments and three of Reed's recent music packages. To receive a copy send $1 and a self-addressed stamped envelope to the workshop address above.