Logic Gates

I got to thinking about logic and about how it might be nice to have some in the ER-301, then I remembered that the envelope probably has a threshold at which it triggers - quick check and it sure does :smile_cat:

So, assuming you have a sound source, Linear VCA and Envelope set up as normal, route two separate streams of gates (with some steps having no gate) into two mixer channels prior to your envelope and the following works:


Set both Mixer Units to -10dB

0 0 = 0
0 1 = 1
1 0 = 1
1 1 = 1


Set both Mixer Units to -20dB

0 0 = 0
0 1 = 0
1 0 = 0
1 1 = 1


It’s not too strict as it only works with relatively short envelopes otherwise you hear the pitch change in the tail of the envelope triggered from the previous gate.

This already provides quite a bit of flexibility and is rather fun!

I am pretty sure proper logic functions have already been promised, but this provides a nice little work around in the mean time :slight_smile:

  • I realise this would work anyway and changes nothing, but not the point heh!


0 0 = 0
0 1 = 1
1 0 = 1
1 1 = 0

This took me a little longer to work out hehe…

For both mixers, after the gate input insert a Linear VCA and set the gate input for that to be the opposite of the mixer channel, set the bias to be 1 and the gain to be -1 to invert the gate!

So for Mixer 1 the input is Gate 1, but then it has a VCA after the input and below the Mixer with input set to Gate 2, bias set to 1 and gain set to -1.

For Mixer 2 the input is Gate 2, but then it has a VCA after the input and below the Mixer with input set to Gate 1, bias set to 1 and gain set to -1.

Both Mixers are set to -10dB

Magic :smiley:


A bit difficult to wrap my head around since I don’t have my ER-301 yet. But I think I get it conceptually.

That’s pretty sharp there, @anon83620728.

Hehe, cheers, it’s a bit weird, it took a little dose of thinking about. I’ve been wanting to do it for a few days and instinctively knew there must be a way, but I was busy with other stuff and couldn’t crack it until this evening :slight_smile:

The one thing I can’t get it to do is respond to no voltage at all, anyone got any ideas?

I wonder i something is possible with a default state of there always being an internal tap tempo unit providing a constant gate? Need to think some more :slight_smile:

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This idea of the tap tempo, or an offset, or actually anything else I tried doesn’t work very well, there’s always some bleed as the VCA closes and opens again. I guess you could get it to work within some pretty tight constraints, but it’s already quite constrained and anything more probably won’t be that much fun!

Going to leave it now, I’m more than happy with the three working logic gates, plenty to have fun with there :smiley:

If anyone has any bright ideas on how to solve the zero voltage problem I’d love to hear them :slight_smile:

This is some mad scientist top level finaggling right here!:heart_eyes:


very clever, I like it!


That is really well thought out. Love a bit of logic, gotta give this a go.


This sounds very familiar, as an echo from long ago… this is basically the same technique used to build logic gates in silicon from transistors, which are basically just VCAs…

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Cheers everyone :smiley:

Yes @bgribble, you’re right, which makes me think I am missing something with the other kinds of gates - I haven’t tried again since I last posted, but I have this feeling it should be possible and probably quite simple! Maybe I’ve been overthinking it. I might have another go :slight_smile:

Of course this is a totally inefficient way to achieve this functionality, but hey, it’s always good fun to push things a little!

Does the 301 have envelopes that can just be triggered? AD/AR maybe? So the gate length is irrelevant? That would give more scope to the envelope shape rather than having to go short to avoid the sustain level changing when gates stop overlapping.

Also (I don’t have one) do you have offset generators in the 301? If so use an offset voltage and then invert your gate input. That will help you work around getting a repose from 0V for other logic types. As you can offset to the binary value 1 (whatever that voltage is) and use an inverted gate alongside that so 0V gate lets the offset through and an inverted gate cancels out the offset. If there’s offset on the device I’m sure you can pipe one in from another module.

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Hey Ben,

Thank you for this, I’ve tried all these ideas and more, but the problem really comes down to when you have to add together these gates, it gets messy! You could be right though, I might have missed something simple last time around which was making it all go wrong hehe!

I said I’d have another go at some point, but I need to feel it to do it and well, the moment of interest and excitement kinda passed for now… I’ll have to wait for it to come around again and catch the wind in my sails! My head is full of other things now :slight_smile:

I suspected you’d have tried all this stuff.

One last thought on it (again just in case it was missed, and I’ve no idea how this works as I don’t have a 301) how about an inverter and offset per CV input. So you’re conditioning these inputs to work the opposite way around. Then mix them both together?

Or you could use an offset from elsewhere in the system and use a VCA inside the 301 to actually let the signal through and mess with it that way too. This could also be inverted at the input to the VCA or the VCAs output (presuming that anyway).

I get the moment of excitement idea, got to run with those things when they happen. Mine can be short lived, really good evening with something then I don’t get round to revisiting for a while. But still for me it’s nice being on here and seeing how things are developing.

Sure… just got to remember that this is essentially a hack, I’m quite sure you can do whatever you want using this method, but it might be tricky to get them all working together in a meaningful way.

I’ll definitely revisit your comments next time I get the urge - they are really helpful thank you :smiley:

You know I’m going to start pestering you to get one hehehe! Imagine an impatient child in the back seat of a long car journey… “Have you got an ER-301 yet?” :smiling_imp:

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haha well we’ll see when that happens. I’m not planning on buying any gear at the minute with the current job situation for me (said publicly I may be loosing some work so trying to make modular / videos work for me more hence a bit more of a push with Patreon etc … these brackets are another shameless attempt to get people over to www.patreon.com/divkid too :wink: ) so kick the back of the drivers seat and keep saying it, I’ll welcome the banter haha.


First post here - my 301 is arriving this week. Relatively new to modular (2yrs) and am intrigued: using your technique, and with regard to or/and, how does a difference in mixer (output?) level yield different results? Happy to be pointed to an external resource. Cheers!

Hey @tomk,

Welcome!! I don’t think being new at something matters too much. I think the idea that you have been doing something a long time and therefore you must know everything is often not true! I know some folks who think they are gods gift, but actually they are quite ignorant on a lot of things, other people who are quite new to something but have the ability to blow my mind - we’re all just different - that’s it :smiley:

Anyway, this works because there’s a threshold level at which the envelope triggers and the mix of the signals determines the level that gets fed into the envelope trigger.

A higher level on both mixers means that any signal at all will trigger the envelope, a lower level means that the signal only gets high enough to trigger the envelope when both inputs are present.

Lets look at AND and say the envelope trigger level or threshold is a hypothetical 1.5.

If the output of each mixer is 0 or 1 then the envelope threshold is only ever reached when both signals are present:

0 + 0 = 0
0 + 1 = 1
1 + 0 = 1
1 + 1 = 2 i.e. over the envelope trigger threshold of 1.5 so it fires!

I would recommend looking up how Logic gates work, the wikipedia articles are useful, lots to read.

Does this help?

Cheers :smile_cat:

Yep this is clear to me, thanks! One other clarification: this technique uses two mixer units, each with unique gate streams, in series on one 301 channel?

Yes, that’s correct!

Enjoy :slight_smile:

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This is a great unit to build if like me you’re only beginning to find your way around the 301. Thanks.

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