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*** 180K THRU-ZERO FM STRETCH ACHIEVED ***
RECENTLY ADDED REWARD
Reward sticker artwork, for backers at all levels. 2in x 3in, water-resistant vinyl.
INTRODUCTION
The E370 Quad Morphing VCO is a DSP-based, quad oscillator Eurorack module from Synthesis Technology. Using improved algorithms from the E350 Morphing Terrarium, the E340 Cloud Generator and the new E330 Multi-Mode VCO, the E370 is the most technically advanced Euro oscillator available. The four VCOs can be individually controlled, used in a set of two pairs, or ganged in “Unison”. A full-color TFT display is used in a ‘shallow depth’ menu system and can show each VCO’s output in real-time (oscilloscope mode). A micro-SD card slot allows users to load in their own custom wavetables and to save & load presets into the E370.
The E370 is 54HP wide and has a depth behind the panel of 48mm (1.89in). It uses a 16-pin shrouded header (standard Euro power, the cable is included) and the target power consumption is +12V @155ma and -12V @40ma. The final power will be available once the project is funded and the module is running the code and the TFT backlight current is determined. About 35% of the current off +12V is determined by the setting of TFT brightness.
BACKGROUND
Two prototypes were built to test the limits of the fastest ARM processors available in non-BGA packages. These breadboards have been thoroughly tested (these are what you will be seeing in the demo videos and audio files). It was decided after testing to wait for faster ARM processors to be available and also ones with more internal memory. Now such processors are available and allow the E370 to be built with the performance our customers expect. We have now built a small test breadboard using the new DSP (STM32F746) and have the “audio core engine” 100% running.
Due to both limitations of the older DSP and available time, what we present here with the prototypes is just a subset of what we will ship with the E370. For example, the prototypes cannot 2-D morph (the E350 X/Y morph) nor do they have the FM mode of the E330. The SPECIFICATION section will detail what the E370 will be able to do right out of the box.
The prototype was called E370/E371 in the videos.
The core algorithms used in the E370 are taken and improved from existing Synthesis Technology Euro modules. Please visit www.synthtech.com and look over the E330, E340 and E350 modules. On the site you will find the manuals and some demos of these modules.
OVERVIEW
The E370 has 3 sections: the display/user interface, 4 VCOs and the jack field.
DISPLAY/UI
The display is a 2.4in (diag.) color TFT (non-touch, 240 x 320 pixels) with a rotary encoder/pushbutton and micro-SD card. The large size of the display allows for “shallow menu diving”, so that every major function (reading wavetables, setting up the mixer, etc) has a minimal subset of pages (the majority is a single sub-page). Data is entered/selected using the rotary encoder which has a “mouse click” shaft. The display is refreshed using high-speed SPI over a DMA channel for minimal ‘lag’.
Please note the prototype uses a smaller screen with 1/4 the pixel resolution
The micro-SD (mSD) slot can handle up to 16GB size cards and uses an industry-standard file/FAT system. There are specific restrictions of the directory structure and file naming convention used, in order for the DSP firmware to access the mSD. These specifications will be extensively documented once the project reaches funding. The file system is “OS agnostic” in the sense users can use PC, Mac, Linux or any OS to read and write data to the mSD.
The mSD card can optionally load and store presets in the E370. The factory presets contain all 192 wavetables from the E350. When a preset is loaded into or saved from the E370, all the wavetables for the 4 VCOs are also stored. Each VCO can have its own set of 64 wavetables. See the CUSTOM WAVETABLES section for more information.
A special mSD card file can be used to field-upgrade the E370's operating system if the need arises.
UI MENU PAGES
The breadboard implements the following ‘pages’ for setting up the operation of the E370. A few more pages may be added to accommodate the added features.
VCO page – sets the overall system VCO setting (individual/2 pairs/unison) and sets each VCO for the type of oscillator (wavetable/cloud/2OP FM). Each of the 3 modes then has a page to setup that specific mode.
Tuner page – each VCO’s output frequency is shown in a large font for easy system tuning
Oscilloscope page – Each VCO’s waveform output is shown on the display
Mixer page – each VCO’s output can be a mixture of all 4 VCOs.
Presets page – load and store presets
SD card page – reads and writes wavetable files into the VCOs
VCO IMPLEMENTATION
The E370 contains 4 identical digital VCOs running 96KHz sample rate audio at 16 bits (internal math is 32-bit floating-point).
1 – COARSE/FINE controls set the initial frequency (no external modulation applied). The range of each VCO is set in the VCO page and can range from 1 cycle in 22 minutes to over 18KHz.
2 – FM controls the depth of frequency modulation by the external CV. The FM can range from DC to over 15KHz without aliasing.
3 – MOD A/B controls – each VCO has 2 programmable modulation CVs and associated attenuator. The function of MOD A and MOD B are dependent on the VCO mode. For example, in Cloud Mode, MOD A is the ‘SPREAD’ and MOD B is the ‘CHAOS’ function of the E340.
It is important to note that the E370 uses higher resolution, lower noise wavetables than the E350. The E350 uses 8-bit wavetables.
VCO TRACKING AND CALIBRATION
The E370 is a collection of four VCOs controlled by a precision crystal oscillator. The temperature drift is < 50ppm (parts per million), which is 0.005%. Any actual drift is therefore a function of the input CV summers, the level-shifter voltage reference and the op amps offset voltage drift. The E370 uses 0.1%, 25ppm resistors in the CV summers, a 5ppm voltage reference to level shift and low-drift op amps. The temperature drift is virtually non-existent.
The tracking
accuracy is based on the design of the input summers mentioned above and the
INL (Integral Non-Linearity) of the A/D converter that reads the CVs and then
converts to a 12-bit word for the E370 to read. The circuity in the E370 is
high-precision so that the tracking is within 3 cents over a 10-octave range.
The E370 features an auto-calibration function, so there are no physical
1V/OCT trimmers that need adjusting (in fact there are no trim pots on the E370
at all). Calibration data is stored and recalled in internal FLASH memory. The
E370 comes factory calibrated using our accurate 1V/OCT test equipment.
However, everyone’s MIDI/CV converter or other pitch CV source may differ. The
auto-calibrate feature is fast and easy to use.
CUSTOM WAVETABLES
The file OS in the E370 allows for reading custom wavetables into the VCOs. The wavetables are 2s-complement signed 16-bit integers (standard .WAV format). Each wavetable is a single-cycle (but can have multiple zero-crossings) and is 256 samples in length. Each VCO can load in 64 wavetables at once. There is no limit to the number of wavetables sets on the mSD card other than the overall 16GB size limit.
STRETCH GOAL – CUSTOM WAVETABLE CREATOR/LIBRARIAN/PRESET MANAGER
Although the overall file requirements for the custom wavetable banks are straightforward, we have added a stretch goal of an additional $15,000 to develop a cross-platform (PC/Mac/Linux) wavetable development package. If the stretch goal is reached, the editor will be available for free downloading.
The environment has 3 separate components:
1 – Wavetable editor and creator. Several different modes to load in existing wavetables or create your own from scratch. Tools included are free-hand drawing, sine harmonics and curve-fitting. Once a waveform is generated, you can then apply wave-folding, clipping, distortion and other effects. Audio preview lets you listen to the ‘raw’ wave. Lower resolution files (like 8-bit samples) are interpolated into the E370 16-bit format.
The Editor comes with the full 192 wavetables of the E350, but expanded to 16-bit, 256-samples format.
2 – SD card librarian. The interface to edit/name/cut & paste/format the physical mSD card. Uses a ‘DOS’ file and a naming structure.
3 – Preset Manager. Allows the state of the E370 VCOs (but not the knob positions) to be loaded from or stored to the mSD card.
Here is a sample layout of the wave editor. Note that the ‘look and feel’ of the editor will be done once the stretch goal is funded.
PROJECT TIMELINE
E370 AUDIO DEMOS
SPECIFICATIONS
The following are the design specifications for the E370. This is the guaranteed minimal set to be delivered. Additional functions may be added as time and DSP bandwidth permit.
Size: 54HP
(10.8in/274.3mm) wide
Depth behind panel: 1.89in/48mm
Power consumption: +12V @155ma, -12V @40ma (based on nominal TFT brightness)
mSD card: 16GB max size supported (mSD card is not supplied)
Control voltage input range: -5V to +5V, 15Khz
Temperature drift: < 50ppm (crystal-controlled)
VCO specifications
Frequency
range: 1 cycle in 22min to 18KHz in 3 ranges (set in VCO page)
Sample rate: 96KHz, 16 bits
Number of wavetable: 64 at any given time (8 x8 matrix as in the E350)
Number of samples: 256
Wavetable mode specifications
Interpolation:
1-D (Z MORPH in E350), 2-D (X-Y MORPH in E350) or none
E350 Phase Mode: yes
E350 Glitch mode: 8 levels of Glitch Energy, or none (default)
Cloud Generator Mode
Number of
virtual VCOs per cloud: up to 8
E340 Sine: yes
E340 Saw: yes
Wavetable clouds: yes (any of the 64 wavetables associated with the VCO can be
used to ‘Cloud’)
E340 Spreading: yes
E340 Chaos/Chaos BW: this is combined into a single control, whose parameters
are set in the VCO page
LFO mode: yes (not available on the E340)
2-OP FM mode
E330 modes:
yes
Additional FM modes: Non-quantized carrier ratios (variable)
Non-sine carrier (any wavetable can be
a carrier)
Risques et défis
Synthesis Technology has been building Euro modules for over 7 years. As a design company that started in 1986, we have engineered over 100 products and shipped over 25,000 units ranging from consumer electronics to military communications hardware. Our first modular product was the 5U MOTM family of modules. Chief Engineer Paul Schreiber was the co-designer of the Radio Shack MG-1 mono synth.
The main risk is in the design of the printed circuit board. Although we have 2 100% functional prototypes, it is not the correct physical size for Eurorack. Once funded, work begins to convert the prototype into 3 individual pc boards: the DSP controller, the pots/display board and the jack board. The DSP board is the only technical challenge, and the schedule allows for 2 iterations to correct possible errors. A 100% working DSP breadboard is currently running all 4 VCOs with only 10% CPU load. We are 100% confident there is no slip due to DSP firmware.
The other schedule risk is having the contract manufacturer miss promised ship dates. For a board of this magnitude, we have doubled the normal delivery time to allow for a large schedule slip at assembly. The hi-grade potentiometers used have a long lead time. These will be ordered the day of funding. We have enough in reserve to build all the necessary prototypes and beta units. Production schedule is such the boards begin assembly the day the pots arrive, as all other parts will be ordered and in stock.
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