Isms questions about 1U Bus, Inverting Attenuator and Gate modules

Hey, wondering if I could get some clarification on a coupe of things.

  1. How exactly does the Bus work? Seeing that there are only three potential ins/outs in both the Bus modules, I can only see two possible ways for it to work, either one set of the three x, y and z jacks are the ins and the other set are the outs, or until cv is sent through them they are neutral at which point they are assigned as either an in or an out. If it is neither of these I am truly befuddled and please explain.

  2. For the Inverting Attenuator, what is the purpose of the constant -5v to +5v that is produced from it?

  3. For the Gate module I do not understand what the last paragraph in the 1U module documentation is talking about, also confused about the static +5v offset, if someone could break it down for me that would be awesome.


I can answer number 2 in that it is able to be used as a manually controllable voltage.

So, with nothing connected to the input, you connect the output to something and are able to change this with the attenuverter as if it was a knob.

Pretty sure that’s the purpose.

First of all, it’s not a row of 1U modules, it’s more like an fulle integrated utility module. It frees up valuable HP so you don’t have to have a lot of simple utilities.

It’s pretty simple x goes to x, y goes to y and so on. It’s basically a way to reduce cable clutter.

A DC offset is useful in a million different ways when you are patching. The most common way is probably to offset an envelope. Many modules have that feature already at the input, but some don’t.

You can use it like a simple envelope generator to generate a CV that can be used to modulate some other modules parameter, like a filter cut-off.

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The BUS is totally passive - just a simple 2jack multiple. It is entirely used to reduce cable clutter while also providing a visual representation of the signal. Thus it’s bidirectional (though we typically pass signals left to right).

The GATE has +5v normalled to the gate input (not cv). The principle use here is to turn a trigger/gate at the CV input into an ‘envelope’ out with the characteristic vactrol slew (fast attack, medium decay). For example, this is a great way to ‘pluck’ the Mangrove’s ‘AIR’ control with a trigger. Typically this causes clicks as the volume is instantly turned up, while the vactrol slew time allows a slight softening for more musical effect.


I haven’t read up on all the Isms features so only have an answer to question 2.

Constant voltages (as the Inverting Attenuator produces) are quite a useful thing in modular synths. They are often used to produce what is know as an offset voltage. Think of it as simply shifting CV up or down. So you have a CV of 2.5v. Adding an offset of -5v means you now have a CV of -2.5v. Adding an offset of +2.5v means you now have a CV of +5v.

Why is this useful? A couple of examples:

  • One of the most common uses of an offset voltage is to transpose a sequence. Try this. Have a sequence running from a sequencer. Run the CV from the sequencer into a mixer. Connect the mixer output to a VCO. Run the offset voltage through a switch or VCA (you don’t have to do this but it means you can automate the offset addition rather than having to manually add it) into the mixer. Start with just the sequence at 100% on the mixer. Have the mixer for the offset at 100% too and open the switch/VCA. The sequence will transpose up or down depending on what offset you have set. Adding a quantizer after the mixer can be a good idea if you are making tonal music.

  • The other thing I use offset voltages for a bit is patching between different manufacturers’ modules. Shifting CV ranges. For example one LFO may expect a CV of 0-10v to get its full range. But the modulation source I want to use produces +/-5v. Again using a mixer, it’s pretty simple to take the modulation source and add a +5v offset. Now my modulation source range is 0-10v which is what the LFO is expecting to see.

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Hi thank you for the information, quite helpful.

Awesome I was hoping that the Bus was bidirectional, that is a really great design. However, after more reading through the isms documentation I understand your comment about working left to right.

All around the modules have an amazingly deep amount of functions.
Really excited to get my hands on the set up.

Got it, Thanks for explaining that for me! Do most attenuators have this function built into them?

Not all, but a lot of them do.

To be clear, the ‘ATTEN’ section won’t add an offset to an input voltage, rather it simply provides a static voltage source when nothing is attached to ‘in’.

When an input is attached, the control attenuates or inverts the signal with the knob.

If you want to add a static offset voltage to a signal, you can use the ‘MIX’ section at the left most of the top row.