# Exponential and Logarithmic Curves

I’ve been meaning to ask about this for a while; I keep wanting different curves on the ADSR Unit and this is potentially possible with what we have now but I am not a mathematician and while if I really put my mind to it I can do maths to quite a high level, I really struggle working out these things sometimes. Also, I am not quite sure how to actually get the feedback!

I mean, I know that to get an exponential curve you just feed back a little of the signal so it has an ever increasing rate… but after that

I guess it would mean dedicating a track to be an envelope, but that’s ok! It’s fun

Anyone got any insights, ideas?

Easiest method: Modulate a linear segment’s speed by itself! If you apply positive speed modulation, it’s exponential. If you apply negative speed modulation, it’s logarithmic. You could test this out by setting the DA to linear and plugging its output into its own speed input.

Mathier method: I’m not sure how to do this in the ER, but in Reaktor I use exponentiation. For instance, you take a segment and square the output to get a more exponential curve, or raise it to the 0.5th power for a more logarithmic curve. The advantage of this method is that you can keep the same segment length while changing the curve shape.

2 Likes

Hehe, I just moved your post - literaly seconds ago

We’re on it - this is great, let me digest…

OK, this is really helpful, thank you, and it sounds like it’s totally doable, until the internal unit outputs become available in the ER-301 then it requires a dedicated channel to do it via the internal routing of the output of that channel back to the mod input of the envelope stages via a mixer/vca!

You would then use that envelope elsewhere in your ER-301 by the same output reference - I think this is gonna work… I’ll try later on this evening and report back!

1 Like

I finally got round to trying this; the shape changes but the overall time for that segment changes too! This is still pretty useful, but I think I was looking for the exponentiation / speed effect more than this shortening/lengthening effect.

I can’t think of a way to do this with the ADSR Unit

1 Like

Did you ever figure out how to use Exponential and Logarithmic curves in the ADSR unit? If so could you give an update on the process?

Sure

Create an ADSR on a global chain

Assign the output of that chain the the portion of the envelope you wish to change to Exp or Log e.g. attack

You apply negative or positive feedback depending on which you want.

Then assign the output of the chain to wherever you want the envelope to be used e.g. into your VCA

2 Likes

I just got a like on the post above, thanks, but the global chain in the example I posted above is now redundant, you can map the output of an envelope back into itself using the ‘locals’ in the assign input selector.

3 Likes

yes, and then use a bipolar vca to control how much the envelope goes back to one of its stages. then when you go positive the stage goes towards log, when you go negative it goes towards expo.
with a careful range mapping you can build useful UI for your custom units

2 Likes

Sorry for bumping this old thread, but as the above proposal to have an envelope modulate itself to achive non-linear curves has the side effect of changing the time of the modulated envelope segment, does it make more sense to have the envelope shaped thru a VCA, with the envelope modulating the VCA gain?

Shouldn’t this give a somewhat exponential shape without time changes?

Yep, that would be equivalent to an exponential.

On a side note: the user you quoted is no longer participating here.

1 Like