Compared to modern-day synthesizers that have extensive modulation matrices – some that feel as if you can modulate anything with anything – the Yamaha DX7, and in turn dexed, has a limited set. That isn’t to say that you can’t create remarkably dynamic and evolving sounds in dexed, it’s just pointing out that there are some limitations. Additionally, given that dexed sorta “hides” the modulation matrix off the main screen, there are challenges to getting what mod sources you have available into your sounds. Let’s take a look at the “undercarriage” of our VST synth, evaluating how we can best use the dexed LFOs and modulation sources we have available.
LFOs
Dexed has one LFO available to use as a source with each voice. It’s a fairly standard implementation – selectable Waveshape, Speed, Delay, and Key Sync. The shape of the LFO waveform offers six options: Triangle, Sawtooth Down, Sawtooth, Up, Square, Sine, and Sample/Hold – the last providing a “random” waveform. Regardless of the waveshape you select, a Pitch Modulation Depth from 0-99 with the P Mod Sens(itivity) parameter. This parameter operates separately in the voice from the controllers that can affect PMD and AMD in the Mod Matrix, which we’ll discuss in a moment.
Similarly to the Pitch Modulation Depth, you can apply the LFO to modulate the Amplitude, or level of operators within a voice. This is handy for tremolo-type effects. Each operator can be programmed to be more or less sensitive to the Amplitude Modulation that’s generated by the LFO – keep that in mind as well.
The Delay parameter is straightforward – 0 means there is no delay between the key being pressed and the LFO effect being applied to the voice, and 99 is the longest delay. LFO Key Sync forces the LFO to start at the beginning of its waveshape upon key down, so if you are modulating pitch and want to ensure that no P Mod is happening at the moment you press a note, then this parameter will help.
Tucked away in the LFO section is also the OSC Key Sync parameter, which doesn’t really have anything to do with the LFO, and probably ended up here due to real estate issues on the UI when dexed was being developed. It’s very similar in function to the LFO sync in that when this parameter is ON, the operator sine waves are forced to start at the beginning of their shape – at zero degrees – when a key is pressed. When this parameter is OFF, the waveform will “free run” and be heard at its current playback phase from note to note. Quite honestly, with dexed generating sine waves as base waveshapes, this difference in most applications will be subtle – except when using an operator as a low-frequency generator as discussed in our Operator walkthrough.
The Pitch EG
The Pitch Envelope Envelope Generator, or Pitch EG, behaves differently to other EGs within dexed and can have dramatic consequences when used. The major difference between the Operator EGs and the Pitch EG is that the Pitch EG is bipolar, meaning it can affect the Pitch positively and negatively within one envelope. In the Operator Level EGs, the value of 0 for any level means at that point in the envelope, the output will be 0, or off at that instant. In the Pitch EG, the value of 50 is our “zero”, meaning that when L1 – L4 are programmed to “50”, there is no pitch modulation. If Levels are programmed to values other than 50, up to 4 octaves (either Level 0 or 100) can be programmed.
The Pitch EG can be tricky to program on dexed if you only rely on the visual representation of the envelope. In the past, I’ve made mistakes by programming something that appeared visually to return to a zero-pitch offset but indeed was off-pitch. Fortunately, dexed also shows the exact parameter value under edit in the “status window” under the lower left corner of the user interface. With this insight, you can ensure that your desired pitch offsets are exactly where you want them to be.
The Modulation Matrix
As we mentioned before, there *is* a limited modulation matrix in dexed, which is somewhat hidden. Where is it? It’s located under the PARM button, in the lower left corner of the UI. Pressing that button displays several parameters. Let’s start with the mod matrix/controller routing assignments first, then review the other parameters available.
Dexed gives you a limited set of controller routings, sensitivity amounts, and switches in its limited modulation matrix. When the DX7 was first released in 1983, MIDI itself was only new, and engineers across companies were just figuring out what to do with this newly developed technology. In the case of the DX7, Modwheel (MIDI Controller #1), Foot Pedal (MIDI Controller #4), Breath (MIDI Controller #2), and Aftertouch (or Pressure) were implemented. These controllers are adjusted via a sensitivity percentage from 0-99 (more likely 100% for 99) before they are applied to their destinations. The possible destinations within dexed are Pitch, Amp, and EG Bias (EG Amount). Even with this limited set of Modulation inputs and outputs, there are plenty of options here for allowing MIDI controllers and Aftertouch to modify your sounds in real time.
As we learn more about basic FM in later editions, we’ll find that taking the Modwheel and routing it to the EG Bias, and then having one Operator respond to that can have a tremendous impact on the sound. The case is similar to routing a modulation source to Pitch – especially considering that FM relies on pitch for most of its waveform-altering magic.
The Other Global dexed Parameters
In the dexed Parameters screen, in addition to the Modulation Matrix programming, you can set the DX7 Global parameters, as well as some dexed specific and modern MIDI and audio settings. As on the DX7, dexed allows a programmable Pitch Bend range to be set. On the DX7, this was programmable to be +/- one octave, but the dexed implementation is +/- 4 octaves. Additionally, different from the DX7 is that the Pitch Bend range for positive range and negative Pitch Wheel can be programmed separately.
Two dexed visual User Interface parameters are also available in this section. First is the availability to show a keyboard along the bottom of the UI – suitable for quick tests while making adjustments to sounds, and the ability to scale the dexed User Interface to 150% of its default size. The latter is especially handy on high-resolution computer monitors – dexed can appear quite tiny at its default size.
The Engine Resolution parameter allows the emulation of three Digital Audio Converter (DAC) types for dexed. “Mark I” emulates the original DX7, which had a 12-bit DAC. “Modern” allows a 24-bit DAC, and the “OPL” series setting emulates the prevalent sound-card FM chips from the 80s and 90s, which had 8-bit DACs. I generally leave this on the 24-bit DAC setting. While I love the tones I can generate from the original DX7, I don’t like the noise inherent in a 12-bit DAC.
The “DX7 Out” and “DX7 Channel” parameters allow the use of dexed to be an editor for a hardware DX7, one of its attractive “bonus” features. “DX7 Out “specifies the system MIDI Output where the hardware DX7 is attached – which MIDI Output and cable. The “DX7 Channel” is its programmed base MIDI channel.
The MPE setting allows the reception of the recent MIDI Polyphonic Expression protocol. If you happen to have an MPE controller, you can enable this parameter to have things like aftertouch and more be polyphonic in nature. Enhanced control and aftertouch information can be processed on a note-by-note basis, beyond what a single channel of aftertouch that affects all notes can do,
The tuning section containing the SCL, KBM, and transposition parameters is a section that is supposed to support standard micro tuning files and thereforemicrotuned playback. While I haven’t ventured into the world of microtuning, the latest version of dexed imports micro-tuning files and allows this functionality.
Wrapping up
FM synthesis as implemented in the DX7 and dexed has a limited set of modulation parameters available in the interface, but they still offer significant ways to twist sounds in drastic ways. There are options, using today’s modern DAW environments to even grow the sound-twisting capabilities further, and we’ll get into that in future installments. In the meantime, we’ll focus on the tools that are immediately at hand as we start to enter the world of FM Synthesis programming in future posts. Thanks for reading!
Resources
- The dexed plug-in:
- The sounds included with dexed:
- SoundEngine’s Rebuild: dexed (Sounds, documentation, and tutorials):
- Our custom programmed banks – Flywheel and Crankshaft: dexed:
- Our dexed series so far:
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