Request: Envelope Controlled Blend

[thehallofshields]

I'm wondering if there is anything out there designed to balance/pan/blend 2 signal paths that you could be controlled by a standard/simple Envelope Detector circuit.

[slacker]

Have a look at R.G's VCA applications document http://www.geofex.com/Article_Folders/VCA%20Applications.pdf

If you take application 4 and instead if an LFO you connect an envelope follower you'll get something that pans between two signal paths, or depending on what you want 4a or 4b might be more suitable.
Obviously it's not quite as simple as just chucking any old envelope follower in there it will probably need some experimenting to get something with a suitable response but it should be doable.

[electrosonic]

Maybe read the stompboxology "Envelope Effects" it contains a envelope controlled mixer among other ideas.

http://www.moosapotamus.net/files/stompboxology-envelope-effects.pdf

(Thanks to moosapotamus for making the stompboxology series available online)

Andrew.

[Mark Hammer]

You may want to ponder whether what you have planned to do with it is best done by an envelope-controlled circuit, or by a simple panning volume pedal.  Even there, the choices remain.  By  envelope-controlled, do you simply want to switch over from signal A to B, based on picking, or do you want active moment-to-moment blending?  Do you want a "default" signal?  How long do you want the insertion of an alternate signal to last for?  How tolerant will the specific signals be of envelope ripple?

A buncha stuff to consider.  You know me;  I just LOVES me some envelope control.  But that doesn't mean it does what one needs in every application.

[Transmogrifox]

Another thing to consider is most compressors have the building blocks you need to do this.  These include the envelope follower and a VCA of some sort.

I don't know your level of skill/knowledge, but a high frequency PWM sort of control might be worth consideration.  A quick and cheap trick would be to copy the MXR envelope filter:
http://www.tonepad.com/getFile.asp?id=113

Rearrange things so the analog switches form a center tap like a pot and you use a second inverter to drive the PWM signal out of phase between the 2.

When you throw away the filter components then you have 2 amplifiers to drive either side and one left to drive the output.

That way you have 2xCD4069 and 1xCD4066 and the only thing that needs to change from the MXR envelope filter is the arrangement of the "IC3" analog switches and then you only need to make unity gain buffers out of the other CMOS inverters from the ones used in the filter.

[~arph]

Here is a design I did.

https://www.dropbox.com/s/a2y1590wg9wkkfd/envelope-mixer_linramp_fresh.sch?dl=0

It is not envelope controlled in such a way that the blend level depends on the envelope, but the blend ramp is triggered by the envelope.
This circuit either mixes in an effects loop or crossfades between direct and the loop.
It's been a while since I made this, but I thought the operation is like this:

When the input level is above the threshold voltage or below the gate voltage the loop is not mixed in/cut-off immediately. When the level is in between the loop is mixed in/faded at the rate set by the pot labeled attack. There is some window shifting/hysteresis going on to ensure solid switching and no sputtering around the gate/threshold levels.

EDIT: Oh and IC3 is a NE571 (doing the VCA stuff). My design is kind of based on that stompboxology article. Also I have some PCBs for this leftover. I'll happily send them over for just the shipping costs, there are two small errors on it that require jumpers. And the PCB mount jacks holes are too small.



Cheers,

Arnoud

[thehallofshields]

Thanks for all the tips.

Do you guys think this could be done with 2 LDR's?1 Negative Coeffecient and 1 Positive Coefficient.

Just stick those in the Feedback Loops of amplifier. Or maybe even a passive mixer.

[~arph]

Yes it can be done with ldrs, I did that initially but I could not get a nice smooth transition with no volume dips, but with some tweaking I think it should be doable. I think the single ic dual vca option is a good one though