SCHLAPPI ENGINEERING THREE BODY User manual

THREE BODY MANUAL
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Technical Information 3
Voltage Levels 3
Sample Rates and Bit Depth 3
Current Draw 3
Module Description and Features 4
Introduction 4
Block Diagram 5
States 6
Controls 7
Inputs 7
Outputs 8
Indicators 8
Modulation Normalization 9
Ratio Normalization 9
Patches to start exploring with: 10
Unmodulated Ratios 10
Phase modulation with ratios 11
Stereo Frequency modulation 12
Theory and Usage 13
Phase Vs Frequency Modulation 13
Through-Zero Eects 14
Modulation Depth 15
Cross Modulation 16
Phase Related Outputs and Stereo Usage 17
External Tracking 19
Conguration Headers 20
Calibration 21
More Recommended Patches 22

Technical Information
Voltage Levels
The Three Body is designed for compatibility ith Eurorack voltage standards. Inputs are
scaled to certain ranges to optimize ADC precision. Inputs and outputs are voltage and
current protected and should not but damaged by any level ithin the Eurorack ecosystem
(-12V to +12v, or 24v peak to peak).
All inputs and outputs are DC coupled.
Sample Rates and Bit Depth
All inputs are sampled at 12bit 96kHz but volts per octave and indexes are over sampled to
achieve 14 bit precision at the expense of a lo er eective sample rate closer to a fe
kilohertz.
The internal sample rate of the Three Body audio path is 12.5MHz to achieve lo aliasing
and high quality modulation eects.
The outputs are implemented ith delta sigma modulation on the FPGA itself and are
approximately 16 bit quality ith 96kHz sample rate.
Current Draw
+12V: 95mA
-12V: 50mA
Inrush current on +12V: approx 200mA
The Three Body has been designed for low power usage, however it will draw a bit
more current on startup than during operation as indicated by the inrush current listed
above.
SIGNAL TYPE LEVEL Notes
Volts per octave CV input -8V to +8V Best tracking between -5V and +5V
Phase or frequency CV
input
-8V to +8V Will clip bipolar signals above 16 volts peak
to peak or unipolar inputs above 8V
Index CV input 0 to 10V Unipolar inputs for envelopes, will clip
below 0V and above 10V
Sync input 0.7V
threshold
Comparator input stage triggers around
0.7V
Output -5 to 5V All outputs are bipolar 10V peak to peak (or
slightly higher, up to 12V peak to peak)

Module Description and Features
Introduction
The Three Body is a phase and frequency modulation toolkit, designed to bring digital
techniques to an analog interface.
It consists of three oscillators hich can be used independently but hich have normalized
connections to facilitate exploration and improvisation.
The separate oscillators can be identied by diering knobs colors and the boundaries
sho n in the panel design.
Each oscillator has three s itches to dene it’s state (or mode) as ell as a collection of
inputs and outputs (identied by the boxes around the jack).
SCHLAPPI ENGINEERING
THREE BODY
FREE
PHASE FM
FM
INDEX SYNC
V/OCT
FM PHASE 1
PHASE 1
INDEX SYNCPHASE 2
PHASE 2
INDEX PHASE FM
FM
INDEX SYNC
COARSECOARSE COARSE
FINEFINE
FINE
FM
INDEX
PHASE 1
INDEX
PHASE 2
INDEX
PHASE
CV FM
CV
PHASE
CV
TRANSPOSE
(COSINE 2)
FREE
TYPE
LIN
EXP
RANGE
LOW / DIV
HI / MULT
LIN
EXP
LOW / DIV
HI / MULT
TYPE
FM
MODE
RANGE
FREE
LIN
EXP
LOW / DIV
HI / MULT
FM
MODE
FM
INDEX
(SINE 2)
V/OCT V/OCT
(SINE 1) (SINE 3)
(SINE 3) (SINE 1)

Block Diagram
OUTER
OSCILLATOR
VCA
FREQUENCY IN
PHASE IN
(CENTER
SINE)
(OPPOSITE SINE)
(10V)
FM INDEX
VOCT/RATIO
SYNC
COARSE/
MULT
FINE/
DIV
FM IN
PHASE IN
WAVEFORM
OUTS
OUTER
OSCILLATOR
VCA
FREQUENCY IN
PHASE IN
(CENTER
SINE)
(OPPOSITE SINE)
(10V)
FM INDEX
VOCT/RATIO
SYNC
COARSE/
MULT
FINE/
DIV
FM IN
PHASE IN
WAVEFORM
OUTS
VCA
CENTER
OSCILLATOR
VCA
(10V)
(10V)
(SINE L)
(SINE R)
PHASE 2 INDEX
PHASE 2
PHASE 1
PHASE 1 INDEX
VOCT/RATIO
SYNC
COARSE/
MULT
FINE/
DIV
WAVEFORM
OUTS

States
At the heart of the three body is a digital logic state machine ith 8 states (per oscillator)
dened by three s itches (per oscillator). This determines hether the oscillator is free,
operating much like an analog oscillator, or tracking in a ratio mode as is necessary for
Cho ning style digital FM. It also determines the behavior of the VOCT/RATIO CV,
frequency modulation, and sync inputs.
Each oscillator also has a phase modulation input hich is not state dependent and a SYNC
input. In FREE mode the SYNC input ill act as a classic hard sync and in RATIO mode the
oscillator ill track hatever signal is at the SYNC input.
FREE/
RATIO
EXPO/
LIN
LOW/HIGH/
DIV/MULT
DESCRIPTION
FREE EXPO LOW LFO with exponential frequency modulation
FREE EXPO HIGH VCO with exponential frequency modulation
FREE LIN LOW LFO with linear frequency modulation
FREE LIN HIGH VCO with linear frequency modulation
RATIO PHASE DIV Tracking oscillator with phase modulation and CV
over division
RATIO PHASE MULT Tracking oscillator with phase modulation and CV
over multiplication
RATIO LIN DIV Tracking oscillator with linear frequency modulation
and CV over division
RATIO LIN MULT Tracking oscillator with linear frequency modulation
and CV over multiplication
TYPE
MODE SWITCHES
for each oscillator
FREE
RATIO
FM
EXPO/PH
LIN
HI/MULT
LOW/DIV
RANGE

Controls
Controls aected by the FREE/RATIO state, works the same for each oscilllator.
Modulation controls are the same for the outer oscillators, but the inner oscillator has
an extra phase input and index control (VCAs) on phase modulation instead of
frequency
Modulation inputs are the same for the outer oscillators, but the inner oscillator has
an extra phase input and index control (VCAs) on phase modulation instead of
frequency
Inputs
Inputs aected by the FREE/RATIO state, works the same for each oscillator
CONTROL FREE RATIO
COARSE/MULT Coarse pitch control Tracking multiplier
FINE/DIV Fine pitch control Tracking divider
INPUT FREE RATIO notes
TRANSPOSE Global Volts per octave
input, adds to all
oscillators pitch
Has no eect Aects all oscillators in
free mode, including
those in LFO mode
VOCT/RATIO Volts per octave input CV adding to
multiplier or divider
Bipolar, can be used at
audio rate
SYNC Hard sync Tracking input threshold at 1V, tracks on
rising edge
INPUT RATIO
PHASE Phase input, breaks internal normalization
PHASE
INDEX
CV control over amount of phase, breaks normalization to 10V Outer osc
FM Frequency modulation input, expo or lin, breaks internal
normalization
FM INDEX CV control over amount of phase, breaks normalization to 10V Inner osc
CONTROL DESCRIPTION Oscillator
PHASE CV Attenuator over phase input outer
PHASE INDEX 1 Attenutor for CV control over amount of phase input 1 inner
PHASE INDEX 2 Attenutor for CV control over amount of phase input 2 inner
FM CV Attenuator for amount of FM input inner
FM INDEX Attenuator for CV control over amount of phase input outer
FREE
COARSE
PITCH
CONTROL
FINE
PITCH
CONTROL
VOLTS
PER
OCTAVE
CV
COARSE/
MULT
FINE/
DIV
VOCT/RATIO
TRACKING
MULTIPLIER
TRACKING
DIVISOR
RATIO
CV
RATIO

Outputs
All outputs are bipolar, approximately 10V peak to peak (may be a bit higher), and
aected by the phase or frequency modulation of the related oscillator.
Indicators
The three large LEDs across the top are all tied to the respective sine wave output of
that oscillator. When this oscillator is below audio rates it will show blue when positive
and red when negative and when at or above audio rates it will show as some
variation of purple.
The four small LEDs across the middle are all tied to the output of the index VCA
next to it. This way you will see both the intensity and the rate of the modulation.
LABEL NAME DESCRIPTION
SINE Sine wave output, modulation subtracting from the phase
COSINE Cosine output, 90 degrees oset ahead of sine output with
modulation adding to the phase. center oscillator only
TRIANGLE Triangle wave output, modulation adding to the phase
SAW Sa ave output, modulation subtracting from the phase
COSAW Saw wave 90 degrees oset ahead of saw output with
modulation adding to the phase. center oscillator only
SQUARE Square wave output, modulation subtracting from the phase

Modulation Normalization
While the three oscillators can be used totally independently, there are some normalization
in place to aid easy exploration as a stereo fm oscillator, drone bank, or even a standalone
noise box.
The inner oscillator PHASE inputs are normalized to received modulation from the outer
oscillators sine outputs.
The outer oscillators FM inputs are normalized to the inner oscillators sine (for the left side)
and cosine (for the right side).
The outer oscillators PHASE inputs are normalized to the opposite outer oscillators sine
ave output (so the left sine goes to the right phase in, and the right sine out goes to the
left phase input).
Ratio Normalization
The t o outer oscillators are set to track the inner oscillator if set to RATIO mode ith no
cable plugged into their respective SYNC jacks.
CENTER
OSCILLATOR
NORMALIZATION
PHASE
PHASE
PHASE
FREQUENCY
PHASE
FREQUENCY
RIGHT
OSCILLATOR
LEFT
OSCILLATOR
RATIO TRACKING
RATIO TRACKING

Patches to start exploring with:
Unmodulated Ratios
Start with all modulation related controls fully counter clockwise. Listen to a sine or
triangle output from the center oscillator as well as one from the right oscillator.
Set the center oscillator to “free” and “high” and the right oscillator to “ratio”.
If the division (the FINE DIV knob) of the right oscillator is set to one (fully counter
clockwise) then turning the multiplication (COARSE MULT) will travel up and down
the harmonic series.
If the division is set higher than one then changing the multiplication value will travel
through a scale of sorts, moving in half octave intervals in the case of a division of 2,
or third octave ratios in the case of a division of three.
Next take a modulation signal like an envelope or LFO, attenuate it with an attenuator
or VCA (this is important) and plug it into the V/OCT RATIO input of the right
oscillator.
Depending whether the range/ratio mode switch is in LOW/DIV or HIGH/MULT this
will add to either the multiplication or division value. If you attenuate the signal
enough you can limit it to only one or two values which will create an arpeggiation
eect if both the mult and div knobs are set fully counter clockwise.
Try also setting the left oscillator to ratio mode and listening to all three oscillators
while sending CV to the outer oscillators, depending on the modulation this can turn
into a wall of arpeggios or slowly moving harmonic drones.
A variation is to set the center oscillator to ratio as well and plug an external oscillator
into the SYNC jack. The center oscillator will then track the external oscillator at a
ratio and the other two oscillators will still track the center oscillator (unless you mult
the external signal and run it into those SYNC jacks as well, then they will track it
instead).