The Jam Corner

GNX Expression Assignments

This article applies to GNX3, GNX4, and GNX3000 units, referred to collectively as “GNX units”. This is an introductory article to using expression assignments; In this article and this I showcase some examples of what this stuff can do for you!

Introduction

Expression assignments is one of the features of GNX units that make it a versatile, programmable tool. This versatility comes in most useful in live situations, but can be effectively applied when recording or mixing, as well.

The three categories of expression controllers are (1) assignable footswitches, (2) assignable expression pedal, and (3) LFOs. On the GNX3000, the footswitches are not assignable, so only expression pedal and LFO assignments apply.

First, let’s talk about how to actually assign things to the expression controllers. In general, the best way to work with these is using the GenEdit or X-Edit interface – both enable you to see all the parameters, and troubleshooting particular effects and settings becomes a whole lot easier. However, the exact same programming is possible using the GNX on-board interface. Here’s how to get there:

1. Begin on the “home screen” (meaning, patch selection; get out of any menu by using Exit). While it is easiest to proceed from the Stompbox mode (for some of the same reason that it’s easier to use the PC interface), but this procedure can also be performed in Bank mode or Recorder mode.
2. In the GNX matrix, scroll down to the very last row using the arrow keys. You can do this by either pressing down repeatedly, or by pressing “up” so the selector wraps around, until the very last row of the matrix is selected.
3. The STATUS button (easy to find, the only button above the matrix) will allow you to select which of the controllers you’re assigning. Your choices, which vary between the three models, will be EXP PDL, LFO, and CTRL FS / CNTRL. Also in this section you may encounter AMP FS and WAH PDL – those are outside of the scope of this article.
4. The first Parameter Knob (these are the knobs used to select/edit the columns of the matrix) lets you select which parameter you’re editing. The list of all possible parameters is available in your manual; here, I will give a few examples of how the controllers can be used. If you don’t want an assignment, you must select “No Link” – the leftmost option.
5. The second and third Parameter Knobs let you select the “minimum” and “maximum” value for each controller assignment. We’ll discuss these settings and how they affect the behavior of each controller.
6. The fourth and fifth Parameter Knobs let you adjust some additional settings for footswitches and LFOs – again, more detail down below.

Footswitch Assignments

For a more in-depth look at footswitch assignments, read the DigiTech GNX Series: Using Controller Footswitches article.

The footswitch assignments are probably the easiest to understand, at least on a basic level. For the footswitches, min value indicates the parameter value when the footswitch light is off, and max value indicates what it is when the light is on. Also, up to three parameters can be toggled simultaneously: these are numbered for simplicity.

On the GNX3, Footswitch 5 is the only one that’s assignable – by default, it’s usually set to Reverb On/Off. How is this assignment achieved? Simple: CTRL1 FS is assigned to “RVBONOFF” parameter; the min value is “Off” and the max value is “On”. CTRL2 FS and CTRL3 FS should be set to “No Link” (in which case min/max values have no effect).

On the GNX4, Footswitches 2, 3, and 4 are all assignable. For simplicity, they’re labeled Controllers A, B, and C respectively (you’ll notice these labels on your interface). Controller assignment selection is labeled as CNTRL A, CNTRL B, and CNTRL C. So, for default operation of Footswitches 2, 3, and 4 (respectively, Stompbox, Mod, Delay) CNTRL A-1 parameter is set to SBOXONOF, CNTRL B-1 parameter is set to FXONOFF, and CNTRL C-1 parameter is set to DLYONOFF. For all three, min=OFF, max=ON; assignments 2 and 3 for each should all be set to “No Link”.

Lamentably, there are no assignable footswitches on the GNX3000.

One additional feature of the assignable footswitches is a toggle mode setting. Two options are TOGGLE and MOMENTARY – these are selectable using the fouth Parameter Knob when a controller footswitch is being edited (i.e., not when you’re editing the expression pedal or LFOs). When TOGGLE is selected, the footswitch will operate as an on/off button: press once to turn on, press again to turn off. In MOMENTARY mode, the footswitch will be at “max” value so long as you hold down the controller, but will go back to “min” value as soon as you let go. In other words, if we took the default setting on the GNX3 (CTRL FS = RVBONOFF), and changed the toggle mode to MOMENTARY, the reverb will only be on when you hold down Footswitch 5.

Keep in mind that besides on/off operation, you can use the footswitches to toggle between two numeric values. In other words, it’s possible to have min/max as a parameter value (such as delay feedback), and go between two values as necessary. We’ll take a look at some examples of this, down the line.

Expression Pedal Assignments

For a more in-depth look at expression pedal assignments, read the DigiTech GNX Series: Using the Expression Pedal

The Expression Pedal assignment works in much the same way as a footswitch assignment. However, two things are different: (1) instead of jumping from min to max, the expression pedal allows to gradually control up to three parameters, and (2) no toggle setting is available.

By far the most common usage for the expression pedal (in factory patches particularly) is the volume (either PRE or POST). Follow the procedure for editing the expression assignment for EXP PDL 1 to Volume Post, and use min=0 and max=99 as the range. You’ll notice that doing so causes the expression pedal to increase/decrease volume everywhere in-between 0 and 99. Of course, you’ll need some practice to get used to the feel of the pedal, to be able to make precise setting changes on the fly.

LFO Assignments

LFO is an abbreviation for Low Frequency Oscillator. The term “low frequency” is generally associated with bass and other low-end instruments; oscillation is a term synonymous with alternating, wavering, and so forth.

Traditionally, LFOs were used in old-school synthesizers as a modulation effect. Modulation effects is a topic in and of itself; however, the basic idea is that of a sound wave (such as that generated by guitar strings) is affected in some way by another wave to produce anything from a subtle effect (chorus is an example) to a drastic sound effect (as you may find with LFOs).

In these old-school synthesizers, the LFO generated an actual, pure tone at a very low frequency (almost below audible range). The frequency shifts up and down very slightly at a set rate. The main sound source is superimposed on the LFO tone, resulting in some very interesting sounds. Synth LFO effects are beyond the scope of this writing, but there’s plenty of material available on the Internet about these.

More recently, LFO generators are used to produce a numeric value rather than an audible tone. In other words, the LFO still has a set rate and a range of values – it moves from the lowest value in the range to the highest, and then back. In some multi-effect processors, such as the GNX series, the shape of the LFO can also be changed. The “speed” of the LFO, expressed in Hz (1 Hz = one time per second; 0.5 Hz = once every two seconds; 3 Hz = three times per second; etc), is adjusted using Parameter Knob 4 when an LFO is being edited.

So we can think of LFOs as automated expression pedals. On the GNX, we can make the "pedal" go between the lowest and highest position at a gradual rate of change (sine), or as a pulse meaning that the pedal position is either lowest or highest, with no in-between (square) - this is more like an automated controller footswitch. The third setting (triangle) is a "middle-ground" setting that causes a straight-line change in value. Parameter Knob 5 will change this setting for you.

There is a dedicated LFO that is used for the Mod section. Effects such as chorus and flanger have an LFO shape parameter (viewable only via a PC editor, but also controllable via, ironically enough, controllers) that determines an actual quality of sound. The LFO speed parameter for the mod section is the rate setting in the Mod. We can use the customizable LFOs in addition to these to create some crazy sonic effects (don’t forget, subtlety is a virtue).

If you ever wondered how the effect is generated on GNX3 factory patch “RIFMATIC” – they used LFOs assigned to pitch effects! Pretty clever stuff… most people think that soft of an effect can only be programmed at the factory and not user definable, but that’s not true! We’ll take a look at some examples later.

Conclusions

Already from a cursory overview, it probably seems obvious how much the power of a Guitar Workstation is augmented with assignable controllers. My recommendation for getting familiar with the controllers is to assign various values at various min/max, speed, and shape settings. I’ll post some examples as well as patch settings used to achieve them in another article.

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