Synth Quickie: Filter Slope


Ah, the elusive Filter Slope: the bigfoot of synthesis.
Some people have seen it, most don’t quite understand it but no one can deny its existence.

Here, I explain how it works and how to use it (by this point, the bigfoot analogy is over).



Filter Slope. I think that’s something that a lot of synth users, don’t really understand. And even when we do understand it, we’re not sure how to use it, what it’s for. So I’m gonna tell you what it is, but more importantly, I’m gonna show you a patch that really makes it obvious. And also one, because it’s so obvious, it means it’s really important that you pick the right slope.

So first things first, what is slope? Let’s take a look at our filter over here. I’m going to turn our resonance down for a second. So as you know, a low pass filter like this, allows you to cut highs off your sound. So when I have my cutoff all the way up, it does nothing. full brightness. And then as I turned it down, Starts to cut highs off for our sound making our sound rounder. Our cutoff is right about here.

Now, a lot of people assume that, you know, whatever your cutoff is, everything above that is just chop right off. But in actuality, it’s more of a gradual cutoff, as you can see here So our cutoff is here and then it just kind of starts to gradually remove some highs. Our slope determines how steep that is. So this is a 12 DB low pass, by increase it to 18, it got steeper. Watch this line increase. Increase it to 24. So as you might guess, the steeper the slope, the rounder the sound gets, right?

Cause we’re cutting off more highs, a steeper slope is removing more highs. So you might think, and I think a lot of people think, well, why not just, you know, if you want it to remove more highs, rather than change the slope, why don’t you just turn the cutoff down. And you’re partially right However, in some cases it really matters. It matters that you change the highs using the slope instead of the cutoff. And this patch right here is a great example.

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So with this patch. See it’s an envelope, modulating our filter’s cutoff, just make an “EEUNG” sound with a ton of resonance, really showing that cutoff. And this is what I had made. This was a patch request on our forum. And someone had put up a patch that sounded like this. And mine sounded like this. It’s really close, but the big difference is, as you notice the hidden patch, it’s brighter.

Its all the sizzle up top. Mine is. so I’m thinking, well, if the hidden one is brighter, mine’s darker, I should just increase my filter envelope amount right? So that it starts higher. I get some more brights in there. So, that’s what I tried. I tried increasing this. So I get, you know, start my filter from a brighter point. Okay. So it was brighter.

Let’s compare that. Now, I achieved the brightness, but it’s different. And more importantly, that EEUNG sound? Right? That envelope, movement, cutoff, resonance, that shape that it’s generating, it’s different now, mine starting higher than the hidden one. Its got more of that at the top, whereas theirs is more of So it loses that really important character. So I knew that wasn’t correct.

And I brought that back down. Yet still, I had this problem. The other patch is a brighter. So how can I make this brighter, without messing with my cutoff? And that’s when it hit me, slope. I can lower my slope to make it a more shallow drop here. And that won’t change my cutoff resonance at all. It’ll just add highs onto it. So let’s see. Let’s try going under 18. That’s better 12. There it is. Let’s hear the hidden one. There it is.

So you see that shape. That really Important cutoff resonance envelope shape, stays exactly the same, no matter what my slope is. But my slope lets me add or remove brightness on top of it. Too bright. All right, well I hope that helps kind of make clear what filter slope does and why you would want to use it.