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!

SA249 C4 Synth User Guide 2

- 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.

SA249 C4 Synth User Guide 3

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.

SA249 C4 Synth User Guide 5

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).

SA249 C4 Synth User Guide 7

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.

SA249 C4 Synth User Guide 9

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 tip­negative, 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).

SA249 C4 Synth User Guide 11

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

SA249 C4 Synth User Guide 12

turn the INPUT knob down. For traditional passive pickups it will help to turn the INPUT level
up.

o INPUT 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

SA249 C4 Synth User Guide 13

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.

SA249 C4 Synth User Guide 14

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).

SA249 C4 Synth User Guide 15

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.