Your sliders cannot be assigned to do anything other than what they are fixed to do. They can assume different modes - but only those finite modes.

The sliders can adjust the volume of each PART. One slider would adjust one PART. There's only one slider that adjusts the volume of multiple PARTs at once and that's your main level slider. Probably not what you want.

Or the sliders can adjust the volume of each element/operator when in a different mode. This isn't what you want. But that explains the other mode. This means each slider is dedicated to ONE PART's individual oscillator components.

To get the sliders in one-slider-per-PART volume mode, you would press the [PERFORMANCE] button which should place you in that mode for most Performances.

You can't assign sliders to anything else - so what they do is what you get.

If you want one controller to change the volume of multiple different PARTs at once - you need to use assignable knobs and use the Common/Audio assignable knobs. Each of these 8 can turn any PART's (or more than one PARTs' at a time) assignable knobs and those can, "in turn", offset volume of the PART. Not a slider - but one controller to change the volume of multiple PARTs at once.

i currently have several performances that have multi-parts along with slit bass, layered brass and layered strings. how can i control the volume for a multi part with just one slider

The Sliders are responsible for individual Part Volumes for the sixteen Parts in groups of four 1-4, 5-8, 9-12 and 13-16. This is when you are in “PART CONTROL”.

The Sliders are also responsible for individual Oscillators within a *selected* Part. Each type of synthesis has eight Oscillators per Part... 8 Elements in the AWM2 (sample) engine and 8 Operators in the FM-X synth engine. This is called “ELEMENT/OPERATOR CONTROL”. Think: drawbars... these would be an excellent example of the individual level controls within a Part (Instrument).

You will find a dedicated front panel button that switches the role of the Sliders from “Part Control” to “Element/Operator” Control... found just to the left of the Sliders.

From the HOME screen touch [SHIFT] + [HOME] to see the OVERVIEW screen.
Press the button [PART / ELEMENT/OPERATOR] to toggle the Slider Function.
Use the button below this to select [1-4/5-8]
Use [SHIFT] + [1-4/5-8] to view Sliders 9-12 and 13/16, respectively.

Each Part has a “Part” Slide Control, and when “Element/Operator” is selected each of the sixteen Parts has eight Sliders, one per Oscillator.

That said, they are always assigned doing some kind of individual Level Control... therefore they are not Assignable.

You have Assignable Knobs! Boy, do you have Assignable Knobs.... The Performance COMMON (referred to as the top or upper level of the architecture, because you can reach all Parts in this Performance from this level) has 8 Common Assign Knobs. Then each of the sixteen Parts has 8 Part Assign Knobs of its own. That’s, 136 Knobs... yes, 136 Assignable Knobs.

So control over Volume output would be done using the massive Control Matrix of Assignable controls. You’ll begin to appreciate why the Super Knob is called “super” when you realize just how you can link movement of Assign Knobs to the movement of this one controller Knob (the one Knob to rule them all, or just those you decide to rule). Those eight Common Assign Knobs are pretty “super”, as well.

Additionally, the movement of the Super Knob can be set to follow an optional FC7 Foot Controller plugged into Foot Controller 2 jack on the MODX back panel.

The Super Knob can be setup to fade out any or all of the Parts together... or in any fashion you desire. You can use it to control all Parts (useful for fade outs), you can have control just the sounds you are playing directly, you can have it control just Parts playing back from a MIDI File or external device, you can have it fade out one configuration while fading in another... you design how and what it does.

In fact, any one of the eight upper level Common Assign Knobs can be used as your overall Volume Control for the Parts you desire. You can move it directly or link it’s movement to the Super Knob and control it with your Foot. The system is far more flexible than you can imagine from just a casual first glance. And as to Assignable functions - it cannot be beat, period.

Extra Credit: Theory of Operation
_ Program each Part in your Performance so that Part Volume is set to be controlled by a Part Assign Knob.
_ Then on the upper Common level of the architecture, link each Part Assign Knob with a single Common Assign Knob
_ Turning this Common Assign Knob will adjust each Part Assign Knob... the default will have the Common Assign Knob assigned to mimic the position of the Super Knob.

If you need specific instructions, give us an idea of what you’re dealing with.

I had a similar situation. My solution was to use a foot controller in FC1 and filter out the bass from it. That way I can control the overall volume with the master volume knob, but still control the volume of my right hand with my pedal. Hope this helps.