MicroDexed (also called MD) is a software which runs on a Teensy(-3.6/4.x) microcontroller. It simulates a well know 6 operator FM synthesizer with some additions (like effects) and is controlled and mostly programmed via MIDI. The sound engine is based on [Dexed](https://github.com/asb2m10/dexed), a famous open-source VST plugin.
## Requirements
To use MD, you need suitable hardware. For example [TeensyMIDIAudo (TMA)](https://codeberg.org/dcoredump/TeensyMIDIAudio/src/branch/master/Rev-1.8) was developed directly for MD. The schematics and layouts are open-source, so you can easily build a TMA board. You can also build it on a stripe grid board or use completely different variants - it's up to you how you build the hardware. Another option (with a few extensions) is the [Teensy Guitar Audio Shield](http://blackaddr.com/products/).
Basically your MD "board" needs the following:
* I2C connector for connecting a LCD display (software is written for a 2*16 character display, but a bigger one should do also).
* 2 Encoders (for each encoder one digital input for the button and two digital inputs for the encoder directions).
* A DA converter supported by Teensy (something like a "audio shield", e.g. the Teeensy audio shield, or (the simplest way) you can use the 12bit DA output pins of the Teensy-3.6 (not possible for Teensy-4.x!)).
* "A way to get MIDI into the Teensy", like the onboard USB port (will not work for USB-MIDI-keybords, because it is not a host port!), the USB-Host port (with soldering a header) or external IO-components for DIN-MIDI.
* A small FAT32 formated SD card.
* The Arduino-IDE and TeensyDuino for compiling and uploading the program code (tested with Arduino-1.8.12 and TeensyDuino-1.52).
The complete hardware build manual for the TMA-board can be found inside the [TMA-Build-Manual](https://codeberg.org/dcoredump/TeensyMIDIAudio/src/branch/master/Rev-1.8/Build-Manual/TMA-Build-Manual.pdf). So for now we expect that you have a running hardware with installed MD software.
* __Turn left/right__: Change the volume (MIDI-CC 7). The volume-change-screen appears when turing and disapears after a short time and you get back, where you left off.
- [<img src="../../images/LCD_characters_green/small_1_inv.png" width="12"/>](../../images/LCD_characters_green/small_1_inv.png) indicates that you are using timbre 1.
- [<img src="../../images/LCD_characters_green/key.png" width="12"/>](../../images/LCD_characters_green/key.png) indicates that you currently use the monotimbral engine.
- [<img src="../../images/LCD_characters_green/bracket_open.png" width="12"/>](../../images/LCD_characters_green/bracket_open.png)[<img src="../../images/LCD_characters_green/bracket_close.png" width="12"/>](../../images/LCD_characters_green/bracket_close.png) are showing which parameter you currently edit with the __PRESET__ encoder.
- [<img src="../../images/LCD_characters_green/note.png" width="12"/>](../../images/LCD_characters_green/note.png) below the timbre symbol(s) indicates that there was an MIDI event (if using a Teensy -4.x different height bars (depending on velocity) are displayed per timbre).
The individual menu items are described below. MD knows three different states:
* Voice/Bank selection
* Adjust volume
* Menu
After switching on, you are in the voice/bank selection. To enter the menu you have to press the volume encoder. You can return to the voice/bank selection by holding down the preset encoder. If you turn the volume encoder, the volume screen appears and you can see which value is set. After a few seconds the system automatically returns to the previous screen.
To select items in the menu, the preset encoder must be turned. On the right side you will see where you are in the menu list. You can select a menu item or jump to a submenu by pressing the preset encoder.
If you want to leave a menu point or change to a higher menu, the volume encoder must be operated.
> You can translate MD with different options and accordingly some features may or may not be available. This also depends on what kind of microcontroller you use. In > this manual the standard options are used. These are:
If you use the *dual-timbral* engine, in many menus a small <imgsrc="../../images/LCD_characters_green/small_2_inv.png"width="12"/> will appear (right of the <imgsrc="../../images/LCD_characters_green/small_1_inv.png"width="12"/>) instead of the key. To switch between the two engines and change their parameters, simply press the preset encoder.
The most important screen will be the selection for the sounds. The screen displays the selected bank number (top left) and the selected voice number (below). Next to the numbers are the corresponding names. The paramater, which is shown in square brackets, can be changed by turning the preset encoder.
MD can manage 100 banks (0-99) and 32 voices per bank. If you turn the encoder over the 32 voices, the first voice of the next bank will be loaded automatically - that is if you are not already inside the latest bank (bank 99). This happens the same way if you go lower than voice number 1.
To switch between voice and bank selection, the preset encoder must be pressed for a long time.
Next to the bank name is the symbol for the active engine. As described above, we use the *mono-timbral* engine for this manual, so the display next to it has a key symbol and is therefore not available. In this case we can not switch between the two instances by pressing the preset encoder.
When the voice is changed, MD sends a voice dump in the background via MIDI SYSEX on its selected MIDI channel. This has the advantage that external devices (like a voice editor on a PC) synchronize the data directly.
By changing (and later saving) this value you can compensate for differences in volume between different sounds. The value ranges from 0 to 127. Default is 100, but you can make the sound louder by increasing the value.
MD comes with some effects. Basically, each MD instance has its own resonant low-pass filter, (mono) Chorus and a separate (mono) delay (500 ms for mono-timbral / 250ms for bi-timbral). This is followed by the placement in the stereo image (see panorama) and a stereo reverb. A complete picture of the generation of the audio signal is stored in the [Repository](https://codeberg.org/dcoredump/MicroDexed/src/branch/master/doc/MicroDexed-Audio-FlowChart.png).
A simple chorus created on the mix of the original signal and a pitch-modulated original signal. The effect is only audible when frequncy, depth and level are all somehow greater than 0.
Parameter:
* Frequency (0-10 Hz)
* Waveform (Triangle/Sine)
* Depth (0-100)
* Level (0-100)
###### (Mono-)Delay
The delay has a feedback loop and can be mixed into the original signal by means of level. Therefore time and level must be greater than 0.
Parameter:
* Time: (0-500ms for *mono-timbral* or 0-250 for *dual-timbral* (on Teensy-3.6))
The reverb is a port of the freeverb. With the *mono-timbral* engine the parameter *Reverb Send* seems to be superfluous and can be set to 100. But if you use the *dual-timbral* version, you can set the amount of reverb send for each of the two sound generators separately. The reverb can only be heard when the roomzize and level, as well as *Reverb Send* are greater than 0.
> Pitch and amplitude modulations are set inside the voice presets by two parameters : *PMD* (*P*itch *M*odulation *D*epth) and *AMD* (*A*mplitude *M*odulation *D*epth)
>
> Those settings cannot be edited using MDs interface (but can be edited via MIDI-SYSEX).
>
>---
> Pitch modulation:
>
> The LFO, internal to MD, will affect all operators in the same way. Its frequency (or rate) and depth are common to all those operators.
>
> Depending on the LFO’s waveform, the effect will sound like a faint vibrato or a large wobble (sine or triangle), a trill (square), a series of random pitches (sample and hold), to name a few.
>
>---
> Amplitude modulation:
>
> The LFO, internal to MD, will affect all operators independantly: Rate will be common, but modulation depth can be set differently on each operator.
>
> If the operator is a carrier, the LFO will affect the general volume of the preset. A sine wave LFO applied to a carrier operator will result in some kind of tremolo effect.
>
> If the operator is a modulator, the LFO will affect the harmonic content of the preset. A sine wave LFO applied to a modulator operator can, in most cases, be compared to an automatic Wah-Wah effect. A sample and hold LFO applied to a modulator operator will result into a series of notes with random brightness.
>
>---
> MDs controller menu
>
> Even if pitch and amplitude modulations are already set inside the Dexed preset, it is still possible to add modulation using external controllers.
>
> Controllers are physical or virtual devices, external to MD, which will have an effect on some parameters, via MIDI-CC messages.
>
> On MD, sources are : Pitch Bend, Modulation, Breath Controller, Foot Pedal, Aftertouch.
>
> Destinations are : pitch modulation by internal LFO, amplitude modulation by internal LFO, EG Bias.
>
> On a physical synth or master keyboard, pitch bend is usually controlled by a wheel or one axis of a joystick, modulation by a second wheel, or the second axis of the joystick, a breath controller by an external pressure sensor, and foot pedal is obvious.
>
> But in fact, if this is a common setting, other combinations can occur, depending on the keyboard/controller and of the musician’s choice.
>
> Those MIDI messages can as well be produced by virtual controllers as DAW, virtual keyboards or MIDI command softwares.
>
> The devices named in this manual refer to the MIDI message, no matter which organ of the controller device produces them.
>
> MD will not produce those MIDI CC messages, but will define their destination, their operating mode, and their intensity.
The pitch of the note can be raised or lowered using the Pitch Bend control (Usually a dedicated wheel or joysitck on a master keyboard). The range can be set up to 1octave on both directions (up/down). *Range* setting defines the highest possible variation: from one semitone to a full octave.
*Steps* define if the control is continuous (step = 0) or by discrete values (steps) of 1, 2 ... 12 semitones.
The other MIDI controllers all have the same modification possibilities. The allocation of modulation can affect different destinations: PITCH (pitch envelope), AMP (loudness envelope), EG (see note below). It is possible to specify targets or any combination of targets but to be able to hear an effect, the voice preset must be configured accordingly.
> Each of the 6 operators has similar settings, no matter if it is a carrier or a modulator.
>
> Amongst those settings, an envelope generator, and an output level.
>
> Output level could as well be named “Gain” and can be compared to a mixer entry fader (in case of a carrier) or a modulation index (in case of a modulator).
>
> EG stands for EG bias, and could as well be called EG depth. It could be compared to the filters EG depth on an analog synthesizer.
>
> When a controller is routed to EG (aka EG Bias), the *Range* value will define how much the controller will affect each operator’s envelope depth.
>
> Depending on a parameter which is internal to the sound engines preset, this will have a different effect, and on many cases, no effect at all.
>
> On MD, this internal parameter is called *AMD* (for *A*mplitude *M*odulation *D*epth) and the controller routed ot EG will only have an effect on the operators when their individual *AMD* is set to a value greater than 0.
> If those operators are modulators, the controller routed to EG will affect the modulation indexes, which have an effect on the harmonic content of the sound (the higher the modulator’s level, the richer the harmonics, leading to a brighter sound).
> If carriers and modulators have an *AMD* setting with a value greater than 0, then the controller routed to EG will affect, at the same time, volume and brightness of the sound.
This parameter sets the MIDI receive channel. MD will react on messages coming from this channel. A channel between 1 and 16 can be selected. Alternatively *OMNI* can be selected if data should be received from all MIDI channels.
> You have to check by yourself if the note ranges you entered make sense. If you set *Lowest Note* to C6 and *Highest Note* to C4 you won't hear anything!
> Each musical instrument has a specific way to produce notes. Some have frets, keys, pistons and will produce discrete notes inside a scale… In european temperament, those notes are usually a chromatic scale (C, C#, D, D#, ...).
>
> On these instruments, it is uneasy, or even impossible, to produce a note between those. The pitch will then abruptly switch from one note to another, it will only vary by steps, and no intermediate pitch will be produced.
>
> On other instruments, such as violin or trombone, the pitch of the note can vary continuously, depending on the exact position of the finger on a string, or the length or the air column inside the pipe: this allows the pitch to slide continuously from one note to the next one. This is known as portamento.
> Depending on the instrumentist technique, this slide can be fast or slow. On MD, this speed is defined by the *Time* parameter. Higher values for portamento rate will produce a fast slide when lower values will result in a slower slide.
>
> In monophonic setting, the choice is given to have a constant (*Full*) portamento (all notes are concerned) or a *Fingered* portamento, which will only happen when you keep the initial key pressed, when playing a new key (legato).
>
> *Glissando* is different in that instead of producing a continuous slide between the pitches of the subsequent notes, it will play all the notes of the scale which are between those 2 notes, like a pianist gliding his finger on the keyboard, or a guitarist on his fretted guitar neck.
> A glide between C3 and E3 will play subsequently C3, C#3, D3, D#3, E3, when a portamento would result in a continuous rising of the pitch, from C3 to E3.
You can reduce the maximum of parallel heared voices if needed. If you recognize glitches in sound maybe reducing the polyphony by one can help to avoid these glitches.
> Maximum polyphony depends on the used Teensy and the used clock speed at compile time. Setting the polyphony to 0 means that no sound will be produced. In *Monophonic* mode you need at least a polyphony of 2.
With these parameters you can adjust the pitch. By means of *Transpose*, this is done in semitone steps (+/- 24 semitones) and by *Fine-Tune*, in +/- 99 cents.
MD can be set to a monophonic mode. In this mode, the envelopes are not restarted when playing legato. In combination with *portamento* this can lead to good sounding effects.
> Please do not confuse this parameter with *Polyphony*! *Mono/Poly* limits the polyphony only indirectly by using only two of the maximum available internal sound generators. If *Polyphony* is set to one, it is still different from playing with *MONOPHONIC* mode enabled. Furthermore, a polyphony of at least two is required for the *MONOPHONIC* mode!
With *Note Refresh* you can influence the behaviour when playing the same note.
For example: if you play a G5 and press and hold the sustain pedal, the next time you strike the same note, another of the maximum available tone generators will hit the note. So the note sounds double and its envelope would also run out seperate for both notes (with a corresponding time delay). This would, however, limit the maximum available notes, since the same note sounds multiple times.
With *RETRIGGERED*, the envelope of the same note is started again and more remaining tone generators are available for other tones.
You should try out this setting and decide yourself which variant fits better.
Presets which have been programmed on some editors, like DEXED for example, would benefit from setting Velocity Level to 12. Other presets coming form other sources or editors, might sound better with Velocity Level set to 100. If you have a hard to play keyboard or just want everything to sound "louder" or "more brilliant" and you don't have to press the keys so hard anymore, you can set a higher value here.
The original Dexed offers three different routines for generating sound, all of which sound a little different. These three engines can also be found in MD and you can try out which one sounds best. *Mark 1* is modeled after an original FM synth (also in the calculation), *Modern* is more modern and more accurate and *OPL* is the attempt to recalculate the sound generation like it was done on OPL chips back then.
Operator enable/disable is a function often used when creating sounds. As an example, let's assume that operator 2 is disabled and we want to enable it again:
Pushing the encoder again turns the operator off (<imgsrc="../../images/LCD_characters_green/small_2.png"width="12"/>). If you turn off all operators (or only the carrier operators), nothing can be heard.
MD can save the additional settings for effects and voice, independantly from the voice/bank presets. Furthermore it is even possible to call up finished combinations of these three variants.
A performance is a combination of an effect setup, voice setup and the selected voices themselves (see below for descriptions of effect setup and voice setup). A performance doesn't store the voice or effect data itself - it stores only references. Different performances can use the same voice or effect config. If you modify a voice/effect config it will affect all performances which use these config.
Voice configurations store all data beyond the sound data itself that is necessary for playing. Voice-Configs should not be confused with the voice data (inside a bank) that describes the sound. All data that are not stored in the voice data are stored there:
Effect configurations save all settings for the effects and are independent of voice configurations or the voices themselves. The following parameters are stored:
A bank consists of 32 voices. These can be sent in a block to MD. Before you can send them, you have to select a bank slot and maybe want to edit the name of the bank on MD's side.
5. Now you can choose to edit the name of the new bank. The blinking cursor is located on the first character (on the left) and can be moved with the preset encoder in this example to the position of character the "4").
10. Now can go to step 5 and edit the other characters like the first one, or you can go one position after the last character to leave the edit screen. An OK prompt will apear on the right.
MD can be operated both in stereo and mono. In addition, the mono signal can also be output on both channels or only on one channel. This is unseful when you want to to use only one cable, but even more, when you want to chain 2 MDs, via Audio IN, and have their outputs separated on 2 different audio channels.
MD has a real MIDI-THRU connection on the TMA circuit board. But if this is not used, it is possible to output all incoming MIDI data via the existing interfaces.
MIDI Soft THRU is also a MIDI merger. When two controllers are plugged into MD, one in the MIDI DIN input, and one on the USB socket, the MIDI messages are merged and sent back to the MIDI DIN output.
Resetting the EEPROM can sometimes be necessary if the internal data has been messed up (by a new firmware). By resetting the EEPROM only the current data is overwritten. All bank/voice data and configurations on the SD card are __not__ affected.
The sound generation (msfa) from the free VST-plugin Dexed. So you can use Dexed as MIDI SYSEX editor or you can use sounds programmed with Dexed on MD. For the original Dexed/msfa software take a look at [Dexed on Github](https://github.com/asb2m10/dexed) and [Music Synthesizer for Android on Github](https://github.com/google/music-synthesizer-for-android).
As mentioned before: you can use external editor software for MIDI SYSEX editing of MD voice presets. Here is a collection of freely available editors:
* (https://www.thisdx7cartdoesnotexist.com/) - not really an editor but a system which generates a bank of voice presets with a KI behind. The names of the voice presets are mostly not readable at the time of writing, but the sounds were not bad.
* (https://dx7.vstforx.de/) - an online editor inside the browser, tested with Google Chrome or Chromium.
* (https://synthmata.com/volca-fm/) - also an online editor whic was written for Volca-FM but also works for Dexed/MD.
