futur3soundz XFM2 User manual

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XFM2 User Manual
©2020 futur3soundz inc.

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Contents
XFM2 User Manual ................................................... 1
Contents ................................................................... 2
Thank you for building XFM2! ............................................................ 5
What is an FPGA anyways? ..................................................................
XFM2 Architecture .................................................................................. 7
Voice architecture ................................................................................... 7
Operator structure and parameters ....................... 9
Oscillators ................................................................................................... 9
WAVE 1, WAVE 2 ..................................................................9
OSC MODE .............................................................................9
OSC RATIO.............................................................................9
Oscillator Waveforms ............................................................................. 9
Interconnecting operators .................................................................. 9
ALGO.....................................................................................10
FEEDBACK...........................................................................10
Oscillators synchronization ...............................................................10
SYNC .....................................................................................10
PHASE ...................................................................................10
Pitch controls ..........................................................................................10
MODE ....................................................................................10
RATIO....................................................................................10
RATIO FINE..........................................................................10
FINE.......................................................................................10
Operator level .........................................................................................11
LEVEL ...................................................................................11
LEVEL L, LEVEL R..............................................................11
VELO SENS ..........................................................................11
Keyboard Tracking ................................................................................11
KEY BP..................................................................................11
KEY LDEPTH .......................................................................11
KEY RDEPTH .......................................................................11
KEY LCURVE.......................................................................11
KEY RCURVE.......................................................................11
Amplitude Envelope Generators ....................................................11
DLY........................................................................................12
L0, L1, L2, L3, L4, L5 ...........................................................12
R0, R1, R2, R3, R4, R5 ..........................................................12
RATE KEY ............................................................................12
EG LOOP ...............................................................................12
EG LOOP SEG.......................................................................12
Amplitude Modulation Sensitivity .................................................12
AMS .......................................................................................12
Pitch Modulation Sensitivity .............................................................12
PMS........................................................................................12
Voice structure and parameters ........................... 13
Voice basics ............................................................................................. 13
Pitch Envelope Generator ................................................................. 13
DLY....................................................................................... 13
L0, L1, L2, L3, L4, L5........................................................... 13
R0, R1, R2, R3, R4, R5.......................................................... 13
RATE KEY............................................................................ 13
EG LOOP............................................................................... 13
EG LOOP SEG ...................................................................... 13
RANGE.................................................................................. 13
VELO..................................................................................... 13
Low Frequency Oscillator .................................................................. 14
WAVE ................................................................................... 14
SPEED................................................................................... 14
SYNC..................................................................................... 14
FADE..................................................................................... 14
DEPTH PITCH...................................................................... 14
DEPTH AMP......................................................................... 14
Program settings ................................................... 15
BEND UP .............................................................................. 15
BEND DOWN ....................................................................... 15
TRANSPOSE......................................................................... 15
VOLUME .............................................................................. 15
PAN ....................................................................................... 15
VELOCITY OFFSET ............................................................ 15
LEGATO MODE................................................................... 15
PORTA MODE...................................................................... 15
PORTA TIME........................................................................ 15
Modulations Section .............................................. 1
Pitch............................................................................................................ 1
AFTER................................................................................... 16
BREATH ............................................................................... 16
FOOT..................................................................................... 16
RND....................................................................................... 16
Pitch LFO .................................................................................................. 1
AFTER................................................................................... 16
WHEEL ................................................................................. 16
BREATH ............................................................................... 16
FOOT..................................................................................... 16
Amplitude LFO ....................................................................................... 1
AFTER................................................................................... 16
WHEEL ................................................................................. 16
BREATH ............................................................................... 16
FOOT..................................................................................... 16
EG Bias ....................................................................................................... 17
AFTER................................................................................... 17
WHEEL ................................................................................. 17
BREATH ............................................................................... 17
FOOT..................................................................................... 17
Arpeggiator ............................................................................................. 17
ARP MODE........................................................................... 17

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TEMPO ..................................................................................17
MUL.......................................................................................17
OCTAVES .............................................................................17
Alternate tunings ...................................................................................17
TUNING.................................................................................17
Creating user alternate tunings .......................................................17
Effects Processors .................................................. 18
Bitcrusher ..................................................................................................18
DEPTH...................................................................................18
Decimator .................................................................................................18
DEPTH...................................................................................18
Filter ............................................................................................................18
LO ..........................................................................................18
HI ...........................................................................................18
Chorus/Flanger .......................................................................................19
DRY .......................................................................................19
WET .......................................................................................19
MODE ....................................................................................19
SPEED....................................................................................19
DEPTH...................................................................................19
FEEDBACK...........................................................................19
LR PHASE .............................................................................19
Phaser .........................................................................................................19
DRY .......................................................................................19
WET .......................................................................................19
MODE ....................................................................................19
SPEED....................................................................................19
DEPTH...................................................................................19
OFFSET .................................................................................19
STAGES.................................................................................19
FEEDBACK...........................................................................19
LR PHASE .............................................................................19
Amplitude Modulation........................................................................20
DEPTH...................................................................................20
SPEED....................................................................................20
RANGE ..................................................................................20
LR PHASE .............................................................................20
Delay ...........................................................................................................20
DRY .......................................................................................20
WET .......................................................................................20
MODE ....................................................................................20
TIME......................................................................................20
FEEDBACK...........................................................................20
LO ..........................................................................................20
HI ...........................................................................................20
TEMPO ..................................................................................20
MUL.......................................................................................20
DIV.........................................................................................20
Effects routing ........................................................................................20
FX ROUTING........................................................................20
Global Reverb ......................................................... 21
DRY .......................................................................................21
WET....................................................................................... 21
MODE ................................................................................... 21
DECAY.................................................................................. 21
DAMP.................................................................................... 21
Output level ............................................................................................ 21
OUTPUT................................................................................ 21
Performance Controls ......................................................................... 22
CTL1H, CTL1L..................................................................... 22
CTL2H, CTL2L..................................................................... 22
CTL3H, CTL3L..................................................................... 22
CTL4H, CTL4L..................................................................... 22
Global settings ....................................................... 23
MIDI Channel .......................................................................................... 23
Layer Mode .............................................................................................. 23
Controlling XFM2 via USB ..................................... 24
D ............................................................................................ 24
I.............................................................................................. 24
R ............................................................................................ 24
W ........................................................................................... 24
S............................................................................................. 24
G ............................................................................................ 24
1 ............................................................................................. 24
2 ............................................................................................. 24
$ ............................................................................................. 24
* ............................................................................................. 24
* ............................................................................................. 24
* ............................................................................................. 24
Appendices ............................................................. 25
Factory tunings ...................................................................................... 25
Uploading and downloading programs and banks ............... 32
MIDI implementation chart .............................................................. 33
NOTE-ON, NOTE-OFF NUMBERS .................................... 33
NOTE-ON VELOCITY......................................................... 33
PROGRAM CHANGE .......................................................... 33
PITCH BEND........................................................................ 33
CHANNEL AFTERTOUCH ................................................. 33
ACTIVE SENSING............................................................... 33
MIDI CLOCK........................................................................ 33
CONTINUOUS CONTROLS................................................ 33
MODULATION WHEEL...................................................... 33
BREATH CONTROL............................................................ 33
FOOT CONTROL ................................................................. 33
VOLUME .............................................................................. 33
PAN ....................................................................................... 33
SUSTAIN PEDAL................................................................. 33
PERFORMANCE CONTROL 1 ........................................... 33
PERFORMANCE CONTROL 2 ........................................... 33
PERFORMANCE CONTROL 3 ........................................... 33
PERFORMANCE CONTROL 4 ........................................... 33

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REVERB LEVEL...................................................................33
TREMOLO LEVEL ...............................................................33
CHORUS LEVEL ..................................................................33
DELAY LEVEL.....................................................................33
PHASER LEVEL...................................................................33
ALL SOUNDS OFF...............................................................33
SYSTEM EXCLUSIVE MESSAGES....................................33
MIDI System Exclusive implementation chart .......................... 34
Calculating 7-bit values ...................................................................... 34
Parameter numbers ............................................................................. 35
...................................................................................................................... 35
Bill of Materials ....................................................................................... 37
A brief note from the developer ..........................................................
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Thank you for building XFM2!
XFM2 is a “classic” FM synthesizer module built with the technology of the XXI century.
Essentially based on a powerful FPGA chip, its massive parallelism allows for an outstanding polyphony, with a
complex dual sound generation architecture, plus two complete sound effect processors, each with up to seven
effects running simultaneously.
The power efficiency of XFM2 core processors results in many hours of operation using standard batteries or
USB powerbanks. This, combined with its small size, makes it ideal for portable sound and music creation.
XFM2 is light, small, compact, fast, inexpensive, simple to build and use. It has no latency and boots
instantaneously. It responds expressively to most common performance gestures and MIDI messages, such as
note velocity, pitch bend, aftertouch, modulation wheel, breath control, foot controller, volume, pan, sustain
switch and chorus and reverb levels. It’s incredibly powerful and capable of creating very colorful, rich, and
expressive sounds.
However, it is a complex creation. Please read through this User Manual to ensure you get the most out of your
new device!
As XFM2 is an ongoing project, make sure to regularly check futur3soundz.com for enhancements, updates, and
expansions.

What is an FPGA anyways?
Back in the 80’s, the world had a rapid flooding of electronic devices. Pocket calculators, portable music players
(cassette), watches, microcomputers, and numerous other devices which had been previously only imagined
suddenly become a reality. Advances in the semiconductor technology, particularly in the integrated circuit,
combined with novel mass production techniques and industrial automation led this fast-paced development
which become the golden age of electronics.
One segment of those semiconductors presented particularly notable kinetics, faster than any other: digital
integrated circuits (ICs). At that time, the technology required to industrially produce ICs was mature enough as
to make them accessible at the consumer market. While invented in the late 50’s, they were limited to military
and government uses for a while, particularly to the Apollo missions.
The best-selling CMOS digital integrated circuit series in history, the CD 4000-4500 series, was released in
1968. As a collection, they provided a complete toolset to design and build any homebrew digital circuit. After
several years in which their adoption was hindered by performance issues derived from fabrication process, in
the late 70’s, almost anyone could purchase a 4-nand gate IC for sub-dollar prices.
Designers started to design all kinds of digital circuitry, increasingly complex. While discrete, mid and large-
scale of integration ICs (up to 10,000 transistors) were sufficient for prototyping and development, large product
series required the “etching” of the final design into an Application Specific IC (ASIC) in order to achieve
maximum cost-efficiency.
The ASIC were (and still are) the perfect electronic solution in terms of speed, energy efficiency, space,
reliability, and cost when there’s a fixed problem to solve, and the number of units to produce is very large.
Creating an ASIC can easily be a multimillion-dollar process, so if you want to have one in your product, be sure
you’ll sell it in the tenths of thousands to offset the costs.
And, make sure you got your design right, as you won’t be able to update or change it once it’s in the field. With
microprocessors, it is possible to update the firmware on it, and then fix or expand some functionality. But the
hardware itself is fixed forever, so the field update and fix scope are limited.
It didn’t take long to the industry to identify the need for a digital circuit that could be completely updated in the
field, at a hardware level: imagine having a device with a huge number of digital gates, which you could freely
interconnect to create complex digital circuit designs, and where every connection would be specified by a
software, which you (or your customer) could update anytime, even after years of shipping the final product.
That device is an FPGA (Field Programmable Gate Array). In 1985, Xilinx invented the first commercially
viable FPGA, the XC2064, which presented the world a new technology and market. The 2064 had 64
configurable logic blocks to create your digital designs.
Xilinx did never stop growing since then and today, 35 years later, XFM2 is using one of their FPGAs—the Artix
A7—with over 33,000 configurable logic blocks. The concept of having gates as a complexity measurement unit
is long gone, as higher conceptual level abstractions serve better to represent design complexity (such as lookup
tables and flip-flops). The FPGAs also started featuring hardened elements (easily utilizable fragments of ASIC),
such as memories and DSP blocks, many years ago, to increase performance and efficiency.
So, how FPGA compare against other alternatives to create digital circuits, such as MPUs (microprocessor units),
MCU/SoC (microcontroller units, system-on-chip) or DSP processors? It’s a tricky question. Essentially, it
depends on what you build into the FPGA. As it’s just a “free digital canvas”, one could easily create a
microprocessor inside the FPGA. Or many: XFM2 has three microprocessors running together to hold all
communication in/out. The advantage starts materializing when you design a perfect digital component for each
block in your device.
So, in XFM2, a few hundreds of design blocks have been crafted and optimized down to a gate level. There are
single-core, and hundred-and-twenty-eight-core components running in parallel, depending on the particular
needs of the block. Everything has been designed to run simultaneously (instead of sequentially, as it is the case
in any of the other solutions). The “hot spots” in the design are then massively parallelized.
And still, any part of the circuit could be updated in the future. In fact, the update could be as deep as a
completely different synthesizer (or anything which has a MIDI input and an audio output).

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XFM2 Architecture
XFM2 is composed by two completely independent 32-voice polyphonic synthesizers, each with its own
individual effect processor. Along this manual, each one of the two synthesizer or effect processor will be
referred as a unit.
This dual-unit architecture allows XFM2 to run as a two-part synthesizer, with up to 64-voice polyphony. A
global reverb unit with individual sends for both units completes the XFM2 design.
Voice architecture
Each synthesizer unit can play up to 32 simultaneous FM voices. Each voice features six FM operators, and each
operator has two individual oscillators.
As in standard FM synthesis, each operator can play a role as a carrier, as a modulator, or both simultaneously.
Sounds in XFM2 are produced by interconnecting operators with different roles, in different ways. The diagram
of those interconnections is usually referred to as an algorithm.
Typically, FM synthesizers offer a limited number of algorithms, with fixed interconnection lines.
As an example, the iconic Yamaha DX7 (the world’s most famous FM synthesizer, and one of the best-selling
synthesizers in history), featured 32 algorithms, or fixed ways to interconnect operators.
In the DX7, all algorithms had only one feedback loop, and only two of them had the feedback loop routed from
a different operator (the rest being operator self-feedback). Even with six operators available, only three serial
FM modulations were possible.
XFM2 extends this concept for vastly expanded flexibility: any operator can receive modulation (and feedback)
from any other operator, or any combination of these. It is possible, as an example, to have operator 1 receiving
modulation from all the others, and from itself, at the same time.
Also, XFM2 features a stereo voice mixing bus. In addition to its carrier/modulator role in the modulation chain,
any operator can be routed to the output, in any defined position in the stereo field, by setting the individual level
sent to each channel.

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Communicating with XFM2
As in any synthesizer, the sound creation in XFM2 is regulated by a set of parameters, which are used to specify
the intended sound characteristics, nuances, responses, and expressive behavior.
There are more than 400 parameters in XFM2 to define any sound, including both the parameters for the
synthesizer engine and the complete effect processors chain. A set of all parameters is then called a program, and
each unit can run its own program.
Up to 128 programs can be saved and loaded to/from the internal memory (EEPROM). Programs can also be
automatically loaded from standard MIDI Program Change messages.
As a module, XFM2 does not feature a user interface for direct interaction with its programs and parameters. It
was designed to act as the sound generation core of a greater system, in which the main user performance
gestures come from any standard MIDI controller.
One of the core design concepts of XFM2 was to create a sound engine module which could be controlled
externally by any user interface builders would imagine, from a few LEDs and knobs to a fully-fledged touch
panel or advanced interface.
There are different options to create, edit, save, and load sound programs, and to tweak all parameters in real-
time:
•Using a computer connected to the USB port (see “Controlling XFM2 via USB”).
This is the most immediate way to change parameters and create, save, and load programs in XFM2.
A basic example of how to interact in this way can be shown in the Excel spreadsheet included in the
zip file, in which simply entering the parameter values will update the device instantaneously. Using the
built-in USB-to-RS232 converter in XFM2, it’s simple to create a complete user interface.
•Using an external interface, using standard serial RS-232 communication.
There are dedicated pins in the XFM2 hardware, which expose its hardware serial interface. It is a
simple task to build and use any inexpensive microcontroller (Arduino, etc.) to serve as a real-time
interface with physical controls for XFM2.
•Using MIDI System Exclusive messages.
Each parameter in XFM2 can be changed by defined MIDI System Exclusive messages, sent from a
MIDI controller or sequencer (see “MIDI System Exclusive implementation chart” for details).
For all three options, every parameter message is composed of a parameter number, and a parameter value.
Along this manual, each feature description will indicate the valid value-range for each parameter. Unless
otherwise indicated, all continuous parameters have a one-byte, 256-value range from 0 to 255.

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Operator structure and parameters
Oscillators
Each operator in XFM2 is composed of two identical and independent oscillators, capable of producing a variety
of waveforms.
WAVE 1, WAVE 2 Select the waveform for Oscillator 1 and Oscillator 2, from 0 to 7.
See Oscillator Waveforms image below for graphical waveform representations.
OSC MODE 0 = Only Oscillator 1 is active
1 = Both Oscillator 1 and 2 are active
OSC RATIO Selects the frequency ratio between Oscillators 1 and 2.
Oscillator Waveforms
Each oscillator in any of the six operators in XFM2 can use any of the eight factory waveforms, indicated in the
graphic below.
All waveforms have been carefully hand-picked with a suitable harmonic content for FM synthesis.
Interconnecting operators
As described previously, all six operators can be combined in flexible ways.
When generating sound, operators are calculated sequentially, in reverse order: first operator to be calculated is
operator 6, then 5, and so on down to operator 1. Each operator has a bitwise matrix parameter which defines
which operators will modulate it.
If the operators set to modulate any other operator have a greater index number (i.e. OP1 being modulated by
OP6), the carrier operator receives standard FM modulation. If it has a smaller number (i.e. OP4 modulated by
OP1), it receives the modulation from a feedback loop.
This approach requires a slightly more complex calculation process to define the algorithm, but in contrast, it
allows for millions of radically different algorithms.

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ALGO
Bitwise parameter, selects which operator(s) will modulate the selected operator:
MSB
LSB
- OP6 OP5 OP4 OP3 OP2 OP1 OUT
Bit 0 (the least significant bit) indicates if the operator output is routed to the main stereo
output.
FEEDBACK Sets the operator self-feedback level.
Oscillators synchronization
Oscillators in XFM2 can have free-running phase (meaning that their phase isn’t affected by the notes played in
any way) or be synchronized (they reset their phase with every note-on event, to a specified value).
When in synchronized mode, the initial phase of each operator can be adjusted in 90-degree intervals, useful to
avoid cancellation effects. Both oscillators share the same initial phase setting.
SYNC
Bitwise parameter, sets individual operators to each free-run (0) or sync to note-on (1).
MSB
LSB
- - OP6 OP5 OP4 OP3 OP2 OP1
Example: Use value 7 (0000 0111) to set operators 1, 2 and 3 to synchronize their phase to
note-on events, and the rest to free run.
PHASE
Sets the initial phase in degrees, for the operator, as follows:
0 = 0 deg.
1 = 90
2 = 180
3 = 270
Pitch controls
Each operator can either have a pitch that tracks the incoming MIDI controller notes or generate a definable fixed
pitch.
MODE
Bitwise parameter, defines if each operator either tracks the keyboard (0) or produces a
fixed tone (1).
MSB
LSB
- - OP6 OP5 OP4 OP3 OP2 OP1
Example: Value 4 (0000 0100) will set operator 3 to produce a fixed-pitch tone, and all the
rest to track the incoming MIDI notes.
RATIO Sets the pitch ratio against the standard MIDI note-based pitch that the operator produces,
in integer values (i.e. 3 = 3:1 ratio).
RATIO FINE Sets the pitch ratio against the standard MIDI note-based pitch that the operator produces,
in fractions of an octave (0 = 1:1 ratio, 255 ~= 2:1 ratio).
FINE Adjusts the operator pitch, in cents (128 = 0 cents).