| br>Hi all.
I've been wanting an envelope follower in my bugmod system for a long time. But for now I have to rely on various tricks. I just found out a new one, best so far, I think.
This relies on a DC-coupled LPG being abused, using the vactrol as both a rectifier and a smoother. Since the bug LPG's are advertised as AC-coupled, meaning filtering out incoming DC with a capacitor on the input, I thought I had to bypass this capacitor... but - it turns out the rev.2 DD1 LPG is already DC coupled (thanks Tom for pointing this out)!
TO TURN A DD1 rev2 LPG INTO AN ENVELOPE FOLLOWER, DO THIS:
*Feed +DC into the signal in (I use a DC from the joystick module, but any source within the system should do).
*Feed the audio to be followed to CV in.
*Set the Init knob to 0, and use the Mod knob to adjust the output level.
*Set it to "lp" or "both" mode (slightly different response)
*Voila - output gives an envelope follower with quite some slew on the downslope...
Here's an oscilloscope picture - lower signal is fed into the CV in of the LGP-env-follower, upper signal is the the output from the LPG module. This was done in "both" mode, but it seems "LP" mode is slightly better, actually.
Yes, the down-slew is slow, and it takes a few seconds to reach zero. Three work-arounds for that:
* offset it downwards, possibly through a diode, to remove the very low parts
* use an exp VCA to modulate something else
* square the signal with the modulator that is conveniently located in the same module! Do this by simply sending the LPG out to both X and Y modulator inputs and setting both levels to max. This will transform the response, scaling down the low levels. This is the best solution, I think - see this oscilloscope pic, using LP mode, and showing the squared env CV on top:
If you set the LPG to "gate" mode, the response is too fast, so you get AM ripples on top of your output CV. Which might be interesting in another way...
* The DC in to the env-follower-LPG could be varied, allowing gating or shaping of the CV without any extra modules.
* Feeding negative DC instead of positive gives an inverted envelope output, which can be patched into another LPG to create a simple compressor or ducker.
/Palle br> br>