Source Audio C4 Synth User manual

SA249 C4 Synth User Guide 1
C4 Synth User Guide
Welcome
Thank you for purchasing the C4 Synth. This advanced piece of gear offers all the sound construction
tools of a classic Eurorack modular synthesizer and packages them in a compact and easy-to-use
effects pedal for guitar and bass. It is essentially a Eurorack modular synth in a box with
unprecedented tracking abilities, lightning-fast response, and countless sound options. Out of the
box the C4 offers six unique and dynamic synthesizer effects. Connect it to the Neuro Desktop Editor
or Neuro Mobile App and unlock this pedal’s true power. Use the Neuro Editors to create your own
synth sounds with its classic Eurorack inspired editing interface or simply call up an effect from
countless presets created by the Source Audio team or the growing legion of C4 users. Create
incredible tones with the C4’s choice of four parallel voices, three oscillator wave shapes, ten-plus
envelope followers, twenty-plus modulating filters, distortion, tremolo, pitch shifting, intelligent
harmonization, programmable sequencing and more.
The pedal comes in a compact and durable brushed aluminum housing with stereo inputs and
outputs, a three-position toggle switch, a simple four-knob control surface, and full MIDI
functionality via its USB port.
The Quick Start guide will help you with the basics. For more in-depth information about the C4
Synth move on to the following sections, starting with Connections. Enjoy!

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-The Source Audio Team
Overview
Six Preset Positions: Use the C4’s three-position toggle switch and two preset banks to save six easily
accessible presets.
Growing Library of Published Presets: For quick access to a world of great tones, try sampling sounds
from a vast collection of published presets created by the Source Audio team and the ever-growing
C4 Neuro Community.
Unprecedented Sound Sculpting Options: The powerful Neuro Desktop Editor (Free download for
Mac and Windows) and Neuro Mobile App (iOS and Android) offer maximum sound exploration
possibilities. Use Neuro’s modular synthesizer inspired editor to create custom C4 Synth presets that
can be burned directly to the pedal, saved to a private cloud based library or shared publically with
other members of the Neuro Community.
Supreme Tracking: If tracking matters to you (and it should), you will be amazed by the lightning
quick, imperceptible latency of the C4 Synth.
128 MIDI Accessible Factory Presets –The addition of a third party MIDI controller with USB host
provides access to any of the pedal’s 128 Factory presets.
Four Independent Voices: Mix together any of the C4’s four independent Voices. Assign any of the
Voices to an oscillator wave shape, monophonic or polyphonic pitch shifter, intelligent harmonizer,
sequencers, or dry signal to distortion, tremolo, and filter effects.
Three Types of Oscillators: Mix and match any of the C4’s three oscillator wave shapes for pure
synthesizer tones. Choose from sine, square, and saw shaped oscillators.
Eleven Envelope Followers: Select from a comprehensive collection of envelope followers with
adjustable attack/decay as well as ADSR triggering envelopes.
25 Filter Effects: Choose from a huge collection of filters, controllable with an envelope follower or
independently modulating LFOs.
14 Different LFO Wave Shapes: Use LFO (Low Frequency Oscillators) to control the modulation of
filter, vibrato, or tremolo effects. Choose from eight different LFO wave shapes, including sine,
square, sample and hold, saw tooth, and more.
Two Programmable 16-Step Sequencers: Run two simultaneous sequencer patterns. Choose from
several preprogrammed sequencer patterns or create custom patterns.
Stereo Inputs and Outputs: Use the Neuro Editor’s panning controls to route each Voice to any
location in a full stereo spread.
Compact Design –The durable, anodized aluminum housing has a small footprint and sturdy
hardware. Dimensions: L: 4.5 in./11.4cm x W: 2.75 in./7cm x H: 2 in./5.1cm (including knobs).
Universal BypassTM –Select either analog buffered or relay based True Bypass.

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USB Port - Class compliant USB-MIDI allows the C4 to work as a plug-and-play device with recording
software running on Mac and Windows recording software or any third party MIDI controller with
USB host. The USB port also offers connectivity to the Neuro Desktop Editor providing access to deep
editing possibilities and pedal firmware updates.
External Expression and Tap Tempo Control —Use the Control Input jack with the Source Audio
Dual Expression Pedal (expression control to multiple parameters) or Tap Switch (adjust LFO rates on
the fly).

SA249 C4 Synth User Guide 4
The C4 Synth: How Does It Work?
Before diving fully into the C4 Synth and its Neuro Editor, it is important to understand the basic
internal layout and signal path. Below is a simple block diagram that illustrates the C4’s Signal Path
and Resource Blocks:
Step 1. The Voices: First in line are the C4’s Voices (there are four of them, hence the name “C4”).
Assigned each activated Voice to its own Sound Source (Sine, Square, or Saw Oscillator / Monophonic
Pitch / Polyphonic Pitch/ Dry Signal). Mix together multiple Voices to create a single amazing preset.
Step 2. Route the Voices: Send each Voice to either Processor Path 1 (Drive 1, Filter 1, etc.) or
Processor Path 2 (Drive 2, Filter 2, etc.). Route each individual Voice through your desired blocks: the
Drive, the Filter, or directly to the Wet Mix.
Step 3. Program Your Resource Blocks: Use the Resource blocks (blue blocks in the diagram) to do
things like control Filter Modulation, set Pitch Shifting intervals, program the Sequencers, and more.
Step 4. Set Your Output Path: Decide which Voice goes to which of the Stereo Outputs.

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Quick Start
Power
To power the unit, connect the included 9V DC power supply to the jack labeled DC 9V on the back
panel. When running a 3rd party power supply, the C4 Synth requires an isolated 9V DC power source
with a minimum of 165mA and a center-negative plug.
Warning: Using a non-Source Audio supply, especially an unregulated supply, could damage the unit.
Please be very cautious when using 3rd-party power supplies.
Guitar/Audio Connections
Using standard ¼” mono cables, connect your guitar, bass, or other instrument to the INPUT 1 jack
and your amp (or the next audio device in the signal chain) to the OUTPUT 1 jack. When running a
stereo rig, also use Input and Output 2.
Once the power and audio connections have been made, the C4 is ready to play.
Brief Knob, Footswitch, and Button Descriptions
Please note that the INPUT/SENS and MIX/VOL knobs each control two different parameters. To
access the secondary parameters (SENS and VOL –printed with white graphics), press the ALT
(Alternative Function) button located on top of the pedal. Upon pressing the ALT button the ALT LED
(small LED on the top face of the pedal) will begin to blink indicating the accessibility of the Alternate
knob parameters. The secondary parameters will remain accessible while adjustments are being

SA249 C4 Synth User Guide 6
made then automatically switch back to the primary parameters five seconds after the last knob
adjustment.
INPUT/SENS Knob: A dual function knob that adjusts the level of INPUT signal going to the processor,
and also the SENSITIVITY of the envelope filter. To access the
•INPUT (the Primary (Default) Parameter): Adjusts the volume level of the input signal. Given
the reactive nature of the C4’s pitch detectors and envelope followers and the varying output
levels of different instruments and their passive or active pickups, it is important to set the
level of signal going to the processor. The C4 also includes a simple process for calibrating
your instrument to the INPUT level (go to the INPUT/SENSE Knob section for calibration
instructions).
•SENSITIVITY (the Alternate Parameter): Adjusts how reactive the envelope filter is to the
incoming signal. If you like to play hard, but still want a smoother, more relaxed envelope
filter, you should turn down the SENSITIVITY. For a sharper response to lighter playing, turn
up the SENSITIVITY.
MIX/VOL Knob: A dual function knob that adjust the overall wet/dry MIX and also adjusts the overall
output VOLUME.
•MIX (the Primary (Default) Parameter): Adjusts the balance between the natural dry tone of
the instrument and affected wet signal. A 50/50 mix of wet dry signal resides at roughly 12
o’clock on the knob.
•VOLUME (the Alternate Parameter) Adjusts the master VOLUME/Output of the pedal. Keep
in mind that the overall VOLUME will likely vary depending on the signal density of the preset.
CONTROL 1 and CONTROL 2: The functions of these knobs vary depending on the selected synth
engine.
Effect Selector Toggle Switch: Use the C4’s three-position toggle switch and two preset banks to
easily access six different presets. First Preset Bank (Indicated by the green center LED): default the
center toggle switch selects between three presets stored in the first bank of presets. Second Preset
Bank (Indicated by the red center LED): Pressing the ALT button on the topside of the pedal opens
access to the second bank of presets. After pressing the ALT button the small LED at the top of the
pedal’s face will start to blink, indicating that the second preset bank is accessible with the toggle
switch. Upon moving the toggle switch the center LED will turn red indicating the current preset is
drawn from the second bank.
Footswitch: Enables or bypasses the effect. Also, pressing and holding the footswitch from the
bypassed state toggles between the first and second preset banks.
ALT (Alternate Function) Button: The small black button located on the topside of the pedal next to
the CONTROL INPUT jack. Pressing the ALT button temporarily puts the pedal into Alternate Control
Mode (indicated by the blinking top center LED). Alternate Control Mode switches from the Primary
to Secondary function of the INPUT/SENS and MIX/VOL knobs. Also moving the center toggle switch
will switch between the Green and Red Preset Banks (go to the Preset Banks section for more info).

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Contents
Welcome..................................................................................................................................................1
Overview..................................................................................................................................................2
The C4 Synth: How Does It Work?...........................................................................................................4
Quick Start ...............................................................................................................................................5
Connections.............................................................................................................................................8
Controls..................................................................................................................................................11
Accessing the Green and Red Preset Banks...........................................................................................14
Three Different Preset Modes ...............................................................................................................14
Universal Bypass TM................................................................................................................................15
External Control.....................................................................................................................................16
Neuro Mobile App & Neuro Desktop Editor..........................................................................................19
Browse, Burn, and Play!! .......................................................................................................................19
The Neuro Desktop Editor .....................................................................................................................19
Daisy-Chaining Neuro Communication..................................................................................................40
MIDI Through the USB Port or Neuro Hub ............................................................................................41
C4 Synth Specifications..........................................................................................................................43
Troubleshooting.....................................................................................................................................44
Frequently Asked Questions..................................................................................................................45
Rubber Feet ...........................................................................................................................................46
Waste Disposal Notes............................................................................................................................46
Warranty................................................................................................................................................47
Version History ......................................................................................................................................48

SA249 C4 Synth User Guide 8
Connections
Input Side Connections
Input 1
This is the primary input for guitar, bass, or other instruments. It can also accept line-level inputs of
up to +6.54 dBV / 8.76 dBu. Connect it to your instrument or other audio source using a mono (TS) ¼”
cable.
Input 2
Input 2 acts as either a second audio input, the data connection for the Neuro Mobile App, or an
input for both audio and Neuro Data simultaneously.
Input 2 as an Audio Input
The tip contact on Input 2 acts as a secondary input for guitar, bass, or other instruments. It is only
active when the C4 is configured with a signal routing option that uses stereo inputs. Connect it to
your instrument (or the previous effect in the signal chain) using a mono (TS) ¼” cable. By default,
the C4 will auto-detect the routing mode. Other routing options are available using the Neuro Mobile
App or Desktop Editor. For more information about stereo routing, refer to the I/O Routing Options
section.
Input 2 as a Neuro App Data Input
The ring contact on Input 2 acts as a data connection for the Neuro App. Connect it to your mobile
device using a stereo (TRS) ¼” cable. It can also accept simultaneous audio and daisy-chained Neuro
data from another Neuro-compatible pedal in the chain, provided that a TRS cable is used. The audio
signal (if applicable) will be on the tip contact of the plug, and the Neuro App data will be on the ring
contact.
Input 2 accepts data from the Neuro Mobile App. Data from the Neuro Hub comes through the
CONTROL INPUT port.

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Output Side Connections
Output 1
This is the primary mono Output. Connect this Output to your amplifier, recording interface, or the
next device in your effects signal chain using a mono (TS) ¼” cable.
Output 2
Acts as either an audio output, the daisy-chain data connection for the Neuro App, or both audio and
Neuro Data simultaneously.
Output 2 as an Audio Output
The tip contact on Output 2 acts as the secondary audio output. It carries an audio signal when the
C4 is configured with a signal routing that uses stereo outputs. Connect it to your amplifier, recording
interface, or the next device in your effects signal chain using a mono (TS) ¼” cable.
Output 2 as a Neuro App Data Daisy-Chain Output
The ring contact on Output 2 acts as a data connection for the Neuro App, passing data from the C4
to the next Source Audio effect in your signal chain. You can daisy-chain the Neuro App data
regardless of whether Output 2 is configured to output audio or not. Connect Output 2 to the next
pedal’s Neuro App Data input (Input 2) using a stereo (TRS) ¼” cable. The audio signal (if applicable)
will be on the tip contact of the plug, and the Neuro App data will be on the ring contact. See the
Daisy-Chaining Neuro Communication section for more info.

SA249 C4 Synth User Guide 10
Power and Control Connections
DC 9V (Power)
Connect to the included 9 Volt DC power supply. The power supply must be regulated at 9 Volts
(direct current), able to source at least 165 mA (milliamps) of current, and the plug should have a tip-
negative, sleeve-positive polarity (the center tip is ground and the sleeve is power).
USB
Connect your computer (Mac or Windows) to the C4’s USB port (denoted by the icon) using a
standard mini USB cable. The USB port handles communication between the pedal and the Neuro
Desktop Editor or a digital audio workstation (DAW). The C4 will also respond to MIDI messages from
an external MIDI Controller with USB host support. The C4 is a class compliant USB device, meaning
that Mac and Windows computers will recognize it automatically. For more information about the
C4’s USB capabilities, refer to the USB section of the User’s Guide.
CONTROL INPUT Port
The 3.5 mm CONTROL INPUT Port connects to external control devices such as the Source Audio
External Tap Switch, Dual Expression Pedal, Neuro Hub, and Hot Hand 3 Motion Controller. For more
information, refer to the External Control and Neuro Hub sections of the User Guide.
ALT (Alternate) Button
The small black button located on the topside of the pedal, next to the CONTROL INPUT jack.
Pressing the ALT button temporarily puts the pedal into Alternate Control Mode (indicated by the
blinking top center LED). Alternate Control Mode switches from the Primary to Secondary function of
the INPUT/SENS and MIX/VOL knobs. Also moving the center toggle switch will switch between the
Green and Red Preset Banks (go to the Preset Banks section for more info).

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Controls
Knobs
ALT (Alternate) Button
The small black button located on the topside of the pedal next to the CONTROL INPUT jack. Pressing
the ALT button temporarily puts the pedal into Alternate Control Mode (indicated by the blinking ALT
Function LED). Alternate Control Mode switches from the Primary to Secondary function of the
INPUT/SENS and MIX/VOL knobs. Also moving the center toggle switch will change the Preset Bank.
There are two Preset Banks the first is indicated by a green center LED, the second is indicated by a
red center LED.
INPUT/SENSE
A dual function knob that adjusts the level of the INPUT level signal going into the processor or the
SENSITIVITY of the envelope filter. See the ALT (Alternative) Button section above for instructions on
accessing the Secondary Parameter.
•INPUT (Primary (Default) Parameter): Adjusts the volume level of the input signal. Given the
reactive nature of the C4’s pitch detectors and envelope followers and the varying output
levels of different instruments and their passive or active pickups, it is important to set the
level of signal hitting the pedal’s processor. For hotter, active pickups it is probably best to

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turn the INPUT knob down. For traditional passive pickups it will help to turn the INPUT level
up.
oINPUT CALIBRATION FUNCTION: We have provided a unique Input Calibration
Function to assure that you are getting the best possible interaction between your
instrument and the C4. The Calibration process is as follows:
1. Turn the INPUT knob all the way down.
2. Continuously pluck your instrument at your average plucking velocity.
3. Slowly turn up the INPUT knob up until the center LED starts flashing red.
This flashing indicates that you have reached the optimum INPUT level.
Leave the knob where it is –the process is complete.
•SENSITIVITY (Secondary Parameter). Adjusts how reactive the envelope filter is to the
incoming signal. If you like to play hard, but still want a smoother more relaxed envelope
filter, you should turn down the SENSITIVITY. For a sharper response to lighter playing, turn
up the SENSITIVITY.
MIX/VOL
A dual-function knob that adjust the wet/dry MIX and the overall output VOLUME.
•MIX (Primary (Default) Parameter): The wet/dry MIX control adjusts the balance between
the natural dry tone of the instrument and affected wet signal. A 50/50 mix of wet dry signal
resides at roughly 12 o’clock on the knob. For a 100% wet signal turn the knob fully clockwise
- for a 100% dry signal turn the knob fully counter-clockwise.
•VOLUME (Secondary Parameter): Adjusts overall output VOLUME of the pedal. Be aware of
that the overall VOLUME will likely vary depending on the signal density of the preset, so
make sure to A/B test the levels between your bypassed and engaged signals and adjust the
VOLUME accordingly.
CONTROL 1 & 2
The functions of these knobs vary depending on the selected synth engine. Use the Knob Assignment
section of the C4 Neuro Sound Editor to learn which parameter has been assigned to the CONTROL 1
and CONTROL 2 knobs.
Effect Toggle Switch
Use the C4’s three-position toggle switch and two preset banks to easily access six different presets.
First Preset Bank (Indicated by the green center LED): by default the center toggle switch selects
between three presets (Circle, Triangle, Square) stored in the first bank of presets. Second Preset
Bank (Indicated by the red center LED): Pressing the ALT button on the topside of the pedal initiates
a blinking pattern from the small LED on the pedal’s face, indicating that the second preset bank is
accessible with the toggle switch. Upon moving the toggle switch the center LED will turn red
indicating the current preset is drawn from the second bank. Follow the same process to switch back
to the green bank.
ALT Button (Alternate Function)
This is a small black button located on the topside of the pedal next to the CONTROL INPUT jack.
Pressing the ALT button temporarily puts the pedal into Alternate Control Mode (indicated by the

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blinking top center LED). Alternate Control Mode switches from the Primary to Secondary function of
the INPUT/SENS and MIX/VOL knobs. Moving the toggle switch while the pedal is in Alternate Control
Mode will switch between the green and red preset banks.
LEDs
Engage / Bypass LED
The Engage / Bypass LED above the footswitch indicates if the effect is active (lit) or bypassed (not lit).
The color of this LED indicates whether the current preset is stored in the first bank (green LED) or
the second bank (Red LED).
The Engage / Bypass LED also plays a role when calibrating the INPUT level. Go to the INPUT/SENSE
Knob section of this manual for instructions on calibrating the INPUT level.
Alternate Function LED
The small LED located between the INPUT and MIX knobs is the Alternate (ALT) Parameter LED.
Pressing the ALT button puts the C4 into Alternate Parameter mode, indicated by the blinking LED. If
a period of 6 seconds passes without moving any knobs or the toggle switch, the Alternate
Parameter LED will stop blinking and the knobs will return to their primary parameter.
The Alternate Function LED also indicates (when lit solid/not blinking) that external control mode
(expression, hot hand, or MIDI) is active.
Footswitch
Enables or bypasses the effect. The footswitch is also used to toggle between the first (green LED)
and second (red LED) Preset Banks. Go to the Accessing the Green and Red Preset Banks section of
this manual for more info on changing Preset Banks.

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Accessing the Green and Red Preset Banks
The C4 can store up to six presets (2 banks of 3 presets) accessible without a MIDI controller or the
Neuro Editor.
•Green Preset Bank (Indicated by the green center LED): By default the center toggle switch
selects between three presets (Circle, Triangle, Square) stored in the first (green) bank of
presets.
•Red Preset Bank (Indicated by the red center LED): Pressing the ALT button on the topside of
the pedal initiates a blinking pattern from the small LED on the pedal’s face, indicating that the
second preset bank is accessible with the toggle switch. Upon moving the toggle switch the
center LED will turn red indicating the current preset is drawn from the second bank. Follow the
same process to switch back to the green bank.
Also, pressing and holding the footswitch from the bypassed state toggles between the first
(Green) and second (Red) preset banks. Note: if “Quick Bank Switch Using Footswitch” has been
selected from the Neuro Editor’s “C4 Synth Hardware Options,” it is also possible to change
preset banks with the footswitch while the pedal is still engaged.
Three Different Preset Modes
Connecting the C4 Synth to the Neuro Desktop or Neuro Mobile App (See the Neuro Section for more
info) allows you to select between three different Preset Modes: Standard (Default), Preset, and
WYSIWYG (“What You See Is What You Get”). To select which mode your C4 operates under, go the
C4’s Hardware Options Menu (the C4 gear icon in the Connection section) and use the Preset /
WYSIWYG menu. Each mode is universal applies to all six presets available in the green and red
preset banks.
Standard (Default) Mode
In Standard Mode each preset engages with a pre-programmed preset, meaning the physical
positions of the knobs do not affect the sound of the preset. It is, however, possible to reach down
and make knob adjustments on the fly. If, after making a knob adjustment, the pedal is bypassed
then reengaged without moving the toggle switch, the sound will continue to reflect the new knob
positions. If the toggle switch is moved (regardless of whether the effect is engaged or engaged), the
pedal will revert to the parameter settings of the saved preset.
Preset Mode
Preset Mode works similar to the Standard (Default) Mode with one key difference, it allows you to
re-save the preset after making knob adjustments. So upon the initial engagement of a preset the
knob parameters will instantly jump to their saved values, regardless of the physical position of the
knobs. However, if you do make a knob adjustment, the center LED will start to blink, indicating that
edits have been made. After making an adjustment you can save the new settings by pressing and
holding the footswitch until the center LED stops blinking (around five seconds).

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WYSIWYG (What You See Is What You Get) Mode
In WYSIWYG Mode the C4 functions much like a traditional effects pedal. It is a” What You See Is
What You Get” experience, meaning that the current physical positions of the knobs will indicate the
settings of the primary knob functions. Note: If you move the toggle switch to a new position all the
primary knob parameters will maintain the settings of the physical knob positions, but the secondary
knob functions (SENSITIVITY and VOL) will revert to their default settings.
Universal Bypass TM
Most effect pedals offer either true bypass or buffered bypass. The C4 Synth contains two separate
circuits for bypass mode, allowing you to choose the method you prefer. The true bypass path uses
signal relays, which are electromechanical switches. This provides an ultra-low resistance path from
the input jacks to the output jacks, which is effectively the same as a single wire. The buffered bypass
path uses extremely low noise buffers, which provide very low output impedance and are effective
for driving long cables or long chains of effects following the C4’s audio output.
Out of the box, the C4 operates in true bypass mode. To select a different bypass mode, open the
C4’s Hardware Options menu in the Neuro Mobile App or Desktop Editor, then select an option from
the “Hardware Bypass Mode” pull down menu.
We recommend using the bypass method best suited for your signal chain. Ideally, the first pedal in a
signal chain is a buffered input followed by true bypass in the rest of the signal chain.
Both bypass methods have pros and cons associated with them. Buffered bypass provides consistent
input impedance so that if the source is susceptible to variations in input impedance (similar to a
guitar pickup), there won’t be a noticeable change in tone. True bypass has the benefit of providing a
dedicated hardwired bypass signal path. The C4 features small-signal relays for true bypass switching
that offer reduced pops and clicks compared to the traditional true bypass switching method using a
mechanical switch.

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External Control
The CONTROL INPUT port opens a variety of external control options, allowing for direct control over
many of the C4’s parameters. It is an input for the, Source Audio Tap Switch, Source Audio Dual
Expression Pedal, or a data port for the Neuro Hub.
The Source Audio Tap Switch
The Source Audio Tap Switch connects directly to the CONTROL INPUT with a 1/8” TRRS cable. The
Tap Switch can be used for a variety of tasks.
•Tap Tempo: Manually tap in the rate of the LFO. Use the Beat Division pull-down menu in the
LFO 1 & 2 block of the Neuro Editor to select the rhythmic subdivision of the tap tempo. The
beat division options are Whole, Half, Quarter, Eighth, Triplet, and Sixteenth notes.
Expression Pedals
The C4’s effects parameters can be controlled directly by a Source Audio Dual Expression Pedal or the
Hot Hand 3 Wireless Controller connected with a 1/8” TRRS cable to the CONTROL INPUT port.
Source Audio’s expression pedals are configured as follows: the tip connection is power, the first ring
is the X-axis expression signal, the second ring is the Y-axis expression signal, and the sleeve
connection is ground.
Ground Power
Y Exp X Exp

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Although the CONTROL INPUT port expects a 4-contact TRRS plug, it is still possible to use a 3rd party
expression pedal with a 3-contact TRS plug (Note: you should make sure the expression pedal’s TRS
configuration is the same as the graphic below). Use a 3-contact 1/4” to 1/8” (3.5mm) TRS plug
converter - the expression pedal’s output will be connected to the C4’s X-axis. For proper operation,
the configuration steps in the next section must be followed when using any expression pedal,
whether from a third party or from Source Audio.
Expression pedals with TS (Tip Sleeve) plugs will not work correctly with the C4.
The resistance/impedance of the expression pedal does not matter. The C4 will automatically adjust
itself to the range of the expression pedal when it is configured.
Configuring the Expression Pedal
Use the C4 Synth’s Neuro Sound Editor to assign expression control to up to three parameters.
Expression editing is accomplished in the External Control block of the Neuro Sound Editor. For more
info on assigning expression control to the C4 go to the External Control section of this manual.
Hot Hand 3 Universal Wireless Controller
The Hot Hand 3 Wireless Effects Controller connects directly to the C4’s Control Input with a 1/8”
TRRS cable and can be used to control up to three parameters. Hot Hand 3 works similarly to an
expression pedal, but rather than rocking an expression treadle to move parameters, Hot Hand
moves parameters with hand motions via its wireless ring. Visit the Hot Hand 3 Page on the Source
Audio website for more details on HH. The Hot Hand has two axes of expression: X and Y. These
signals are carried on the two rings of the TRRS cable that comes from the Hot Hand receiver.
Ground Power
Expression
Ground Power
Y Exp X Exp

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Configuring the Hot Hand
Use the C4 Synth’s Neuro Sound Editor to assign Hot Hand control to up to three parameters. Hot
Hand expression editing is accomplished in the External Control block of the Neuro Sound Editor. For
more info on assigning expression control to the C4 go to the External Control section of this manual.

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Neuro Mobile App & Neuro Desktop Editor
The C4 Synth was designed to be a simple plug-and-play effects pedal. Straight out of the box, the C4
offers six great sounding guitar/bass synth effects, but connecting the C4 to the Neuro Mobile App
and Neuro Desktop Editor a vast Library of easy-to-access Presets created by the Source Audio team
and the ever-growing community of C4 Synth users. The Neuro Editor also offers a super-powerful
Sound Editor for creating, saving, and sharing your own custom Presets.
Browse, Burn, and Play!!
It’s just that easy. If you don’t have time to dive into the Sound Editor, but you want a quick listen to
the vast landscape of sounds the C4 has to offer, simply jump to the Cloud and check out all the
available User Presets. When you find something your love, simply hit the BURN button and upload
that Preset directly to your C4 and bring it to the next gig. For more info on Burning Presets to your
C4 go to the Cloud section of this manual.
The Neuro Desktop Editor
The Neuro Desktop Editor is an excellent tool for accessing, creating, and organizing Presets for your
C4 Synth. The Desktop offers an expanded collection of deep editing parameters, and an advanced
cataloging system for naming and storing C4 presets. The Desktop is also a tool for installing the
latest updates to your C4 Synth firmware.
Downloading and Connecting the Neuro Desktop Editor
The Neuro Desktop Editor is a free download for Mac and Windows PCs. To download the Neuro
Desktop, go to the Source Audio Downloads page. In the Software tab click and download the
appropriate file. The latest firmware versions for the entire line of One Series pedals, including the C4
Synth, are included with the Neuro download. If there is trouble installing the software, select
System Preferences // Security and Privacy // Open Anyways.
After the downloading process, open the Neuro Desktop Editor and connect your C4 Synth with a
USB Type A male to mini Type B male data cable (Warning: don’t use a charger cable). Connect the
cable from the mini USB port on the pedal to the USB port on your computer. Once you’ve made the

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connection a blue box will appear in the Connections field of the Neuro interface indicating that the
C4 is ready for editing.
If your C4 Synth is in need of a firmware update, the Firmware Update icon (the arrow icon) will be
framed in yellow. Upon clicking the arrow icon, you will be instructed on the updating procedure.
(Note: It is important disconnect all other Source Audio pedals and turn off MIDI software during the
firmware updating process.)
Neuro Desktop Editor User Interface
The Neuro Desktop’s user interface features three primary sections: Connections, Preset Editor, and
Presets.