quacky envelope follower

[birt]

i want to use the nurse quacky envelope follower to control the volume of another signal path. i was thinking to connect a led to the transistor of the envelope follower in some way that i could use that with an LDR to control the level of a different signal.

can i connect 9V to the anode of a led and connect the cathode to the collector of the transistor? will that dim the led with the guitar signal?

To control volume with an LDR, should i put it in series inbetween gainstages (tremulus lune) or from a signal wire to ground? i know both work but i don't know the pros and cons.

[StickMan]

Using an envelope follower to control volume seems like a redundant idea.  After all, the volume of the signal is the envelope, so whatever this other signal path is (assuming it's from the same instrument), it is already following the envelope.

Am I missing something?

On the other hand, it might be cool to build a generalized envelope follower to replace a control pot on some other device  -  like running the drive control on an overdrive.

[birt]

like i said, it's gonna be used to control the volume of another signal. not the same guitar signal.

[Mark Hammer]

What you describe encompasses both ducking (signal A is only heard when signal B declines below some level) and gating (signal is only heard when signal B is present).  Many gates permit the insertion of a different source of control signal than the actual audio signal being gated.  Ducking circuits can be easily found in a number of places.  The PAiA Ducker circuit is available at their website (www.paia.com).

[birt]

but both effects are more complicated than what i want. basicly i want to make a tremolo with an envelope follower instead of an LFO. i just don't know how to hook up a led/ldr to that envelope follower.

my guess is 9V to led anode, led kathode to resistor (current limiter) resistor to collector, emitter to ground.

[birt]

will the led at the right of this schem dim with the envelope of the guitar signal?

[Mark Hammer]

but both effects are more complicated than what i want. basicly i want to make a tremolo with an envelope follower instead of an LFO. i just don't know how to hook up a led/ldr to that envelope follower.

When you say "instead of an LFO", I'm figuring that you mean you want the tremolo rate to vary with strength of playing, instead of being a fixed rate.

I think the circuit you present may work, although whether it will have the optimum characteristics is another thing.  One of the tricky things about envelope responsive LFO rates is that often you really want them to respond to averaging over phrases rather than individual notes.  The half-wave rectifier shown lends itself more to note detection, although the larger cap value (22uf instead of 4.7 or 10uf) helps in smoothing out the envelope so that it starts to average out over multiple notes.

I have a Line 6 Tap tremolo that includes a dynamic/envelope-controlled speed feature.  One of the things that beciomes quickly apparent when you work with it is that the envelope-sensitivity and the default and maximum speed interact, and need to interact in an intelligent way.  So, if the default rate is quite slow (e.g., .8-1hz), you can't zip up to faster rates like 4-5hz too quickly or else the effect is a little jarring.  Same goes for decelleration.  In your case, the 50k trimpot provides a relatively low imnpedance path to ground for the 22uf cap to discharge.  You may want to increase the value of that trimpot if possible.

It may be useful or interesting to have the same LED control not only rate but modulation depth such that stronger picking makes the tremolo more intense as well as faster.  Not having any idea about how you intend to provide/control tremolo depth (i.e., how much attenuation occurs between maximum and minimum volume), I can't offer any ideas about how to productively use the same LED to affect a suitably-placed LDR.

I have not worked with a "dynamic" tremolo that slows modulation rate in response to stronger picking, so I have no idea if it sounds interesting or not.

Finally, if the intent is to use the LED to control an LDR resistance that governs speed, you will probably want to have: a) a variable resistance in series to determine initial speed, and b) some means of adjusting how much the LDR change alters speed.  This latetr aspect can be addressed somewhat by the sensitivity control, but sensitivity and what gets changed under low and high-sensitivity settings are two separate things.

[birt]

i really appreciate your explenation, i keep on learning. but what i meant by no LFO is that i just want to control the volume with that LDR, not the rate of an LFO

but now i know this might work the way i want it to so i'm happy

[Mark Hammer]

i really appreciate your explenation, i keep on learning. but what i meant by no LFO is that i just want to control the volume with that LDR, not the rate of an LFO

I find this confusing.  Why use the volume of something to control its volume?  Why not let the volume BE the volume?  Something is missing here.  Do you mean you want the LDR to control the depth of the effect?

but now i know this might work the way i want it to so i'm happy

Great!

[birt]

i use the volume of one signal to control the volume of another completely different signal. does that make sense?

[Mark Hammer]

NOW it does.

Look into external gating; the control of a noise gate by a second signal.  One of the smartest uses of this I have ever heard was the old David Bowie Song "Let's Dance".  Producer Nile Rogers fed all the brass/horn channels to a noise gate and controlled it with his rhythm guitar strumming.  This gave the entire horn section a very different kind of feel that was surrealistically precise.