u-he Diva StackIndex Dual Filter Trick

Most producers assume u-he Diva can only run one main filter at a time. With the Diva StackIndex modulation source you can get two different filter responses inside a single patch: one stacked voice leans toward low pass, the other toward high pass. The result is a wider, more detailed sound without loading a second Diva. Here's exactly how I set it up, step by step, with screenshots.

How the Diva StackIndex dual filter trick works

Stack is Diva's unison: it plays several voices for every note. StackIndex is a modulation source that gives each of those stacked voices a different value. With Stack set to 2, one voice gets a negative value and the other a positive one. Route StackIndex to a control and the two voices move that control in opposite directions.

Point it at the LP/HP MIX of the Uhbie filter, and one voice becomes darker while the other becomes brighter. You still see one filter on screen, but you hear two.

Step 1: Select the Uhbie filter

Open the filter menu and select VCF | Uhbie.

Uhbie is a smooth 2 pole state variable filter, and it's the key to this trick. Its LP/HP MIX control lets you blend continuously from low pass through band reject or band pass to high pass. The other Diva filters have fixed modes, so they can't do this smooth crossfade.

Step 2: Set Stack to two voices

In Diva's Voice section, set Stack to 2.

This creates two versions of every note you play. For now, set the Stack Tune offsets to zero so you can hear the filter effect without extra detuning. That way you know the width you hear comes from the filters and not from pitch.

Remember that stacking uses extra voices, so you may need to raise Diva's maximum voice count when playing bigger chords. A four note chord with Stack 2 already needs eight voices.

Step 3: Centre the LP/HP MIX control

Go back to the Uhbie filter and put the LP/HP MIX knob in its centre position.

This gives StackIndex room to push one stacked voice toward low pass and the other toward high pass. If the knob sat at one end, one voice would have nowhere to go.

At the centre you can choose BR for a band reject (notch) response or BP for a band pass response. BR keeps more body in the middle position, BP sounds thinner and more focused. Try both: it changes what happens between the two extremes.

Step 4: Change the MIX modulation source to StackIndex

Underneath the LP/HP MIX knob, change the modulation source from ENV 2 to StackIndex.

Make sure you change the ENV 2 source underneath the MIX control, not the ENV 2 source beside the main Cutoff knob. They look the same, and changing the wrong one gives you a completely different (and much less useful) result.

StackIndex assigns a different modulation value to each stacked voice. With Stack set to two, one voice receives a negative value while the other receives a positive value.

Step 5: Dial in the StackIndex amount

Slowly increase the small modulation amount knob beside StackIndex. As you increase it, one voice moves toward the low pass side of the Uhbie filter while the other moves toward high pass.

Adjust the amount by ear. You don't always need to turn it all the way up: a smaller amount often gives a smoother, more usable result. I usually stop at the point where the sound gets noticeably more detailed, before it starts sounding like two separate instruments.

Step 6: Add stereo width

For extra width, open Diva's Amplifier & Pan section.

Change Pan Mod to StackIndex and slowly increase the modulation amount. This places the two filtered voices on opposite sides of the stereo field: the darker one on one side, the brighter one on the other.

Start with around 20 to 40% rather than jumping straight to maximum width. Full width sounds impressive solo but often feels disconnected in a mix.

What does this Diva trick actually do?

Diva still shows one filter module, but Stack creates two complete voices for every note. StackIndex then gives those voices opposite filter settings. The result works like a parallel dual filter sound:

• One voice provides warmth and body through low pass filtering.
• The other voice provides brightness and air through high pass filtering.
• Optional StackIndex panning separates both responses across the stereo field.

This works especially well for melodic house pads, atmospheric leads, arpeggios and evolving plucks.

Be more careful when using it on bass sounds. Too much stereo separation can weaken the low end when the track is played in mono. On a bass I either skip the Pan Mod step completely or keep the patch for a higher layer that sits above a separate mono sub.

Take it further

Once the basic setup works, try adding a small amount of Stack Tune for gentle detuning. Now the two voices differ in pitch as well as tone, which thickens pads nicely.

For moving textures, you can also multiply a slow LFO with StackIndex in Diva's Modifications panel. Multiply outputs the product of two modulation sources, so the LFO swings up and down while StackIndex flips the direction for each voice. Use the result to modulate the Uhbie MIX, and the two voices travel in opposite directions through the filter.

As one voice becomes darker, the other becomes brighter. On a long pad chord this sounds like slow, organic movement, without any extra effects.

If you like this kind of detail, the same thinking works across Diva. I cover the modulation layout and the Modifications panel in how to use u-he Diva properly, and more ways to build width in how to layer synths for deep, atmospheric electronic music.

Common mistakes

Changing the wrong ENV 2 source

The StackIndex source must go under the MIX knob of the Uhbie filter. If you change the source next to Cutoff, one voice just gets brighter and the other darker in cutoff, which is a different effect.

Leaving Stack Tune detuned while setting up

If the stacked voices are detuned, you can't tell what the filter is doing. Set Stack Tune to zero first, add detune at the end.

Running out of voices

Stack 2 doubles the voices you need. If notes cut off in chords, raise Voices. And keep an eye on CPU: the u-he Diva CPU guide explains why stacking is expensive and how to keep it under control.

Too much width

Maximum Pan Mod plus maximum MIX amount can make the sound fall apart in mono. Check it in mono before you commit.

FAQ

What is StackIndex in u-he Diva?

It's a modulation source that gives each stacked (unison) voice a different value. With Stack 2, one voice gets a negative value and the other a positive one, so any control you modulate with it moves in opposite directions for the two voices.

Does this work with other Diva filters?

The smooth low pass to high pass blend needs Uhbie, because its MIX knob crossfades between the responses. You can still use StackIndex on the cutoff of any filter for a simpler brighter and darker split.

Does the StackIndex trick use more CPU?

Yes. Every note plays two full voices, so expect roughly double the load of the same patch without Stack.

Is it mono compatible?

The filter part is fine. The Pan Mod width is what can cause trouble in mono, so keep it moderate and check your mix in mono.

With only StackIndex and the Uhbie filter you can turn a simple Diva patch into a wide, detailed dual filter texture, without another synth layer or a pile of effects. Try it on the free Glow Diva presets first, and if you want more pads and plucks to experiment with, the full Glow pack or the Complete u-he Diva Preset Bundle gives you plenty to work with.