In making a reverse pedal:

[rockgardenlove]

So, I already have a Boss Slow Gear clone that I'm gonna make, but it's not convincing enough a reverse sound for me.  There's a Danelectro pedal that gives a nice shot of white noise at the very end of the reversed note.  I was thinking I could just make a separate little circuit that would insert a little shot of noise when the note passes a certain threshold.  So I was thinking of using an envelope detector to output a control voltage.  When the voltage rises to a sufficient point, I'd use a FET or something to inject some noise.

Thoughts?
One thing I'm not sure how to do is to bias up the noise-injector.  How would I do this?
Thanks!

[Paul Perry (Frostwave)]

I guess a rough envelope follower, and the output of that goes to a comparator that triggers an astable flip flop that controls the noise.
I would use a 555 timer, you might not even have to use the envelope follower, just rely on the peak of the audio (when it exceeds the 555 threshold) to flip the 555 for a predetermined time, the output from the 555 does the noise control.

[Mark Hammer]

Properties of a "normal" plucked string:
1) harmonic content clustered near the onset of vibration followed by rapid decline of treble and "regression" to fundamental and lowest harmonics
2) initial burst in amplitude followed by various "fallbacks" to steady state amplitude, depending on string-type, bridge, body-type, etc
3) finger vibrato (pitch variation) introduced near decay phase of note cycle to extend vibrational life of note

Properties of an ideal reverse-tape simulation
1) initial vibrato, followed by more stable pitch
2) fade in of volume with quick burst of level and abrupt decay
3) gradual increase in treble, followed burst in harmonic content just prior to decay

Slow Gear-like pedals of the non-digital type (where there is no direct reverse-sample) generally apply a kind of sophisticated noise-gate circuit that accomplishes #2 above reasonably well (though it tends not to mimic the peak transient terribly well), but make no attempt to mimic #1 or #3.  What you are contemplating is essentially #3.  In some respects, what you really want is not just some sort of automatic reverse attenuator, like the Slow Gear does, but an automatic gain-adder that introduces the possibility for salvaging a bit of treble at the tail end of the signal. 

This is hard to do for a few reasons.  First, the amount of gain to be added would need to be significant, given the string's natural tendency to lose energy.  You can get past that a bit if you are willing to have the rise time fast enough that it can take advantage of the string's remaining energy earlier in the decay cycle.  Of course, that means you can only simulate quick-decaying notes played backwards, and not those delicious slow-creepers that make us want reverse-effects in the first place.  The second reason why it is hard to do is that as you get well past the initial attack of the plucked string, there is much less treble content.  Remember, we are trying to mimic the properties of a reverse-played tone on forward-moving signal, so you have to ask whether the real-time string signal itself provides the raw materials to do what needs to be done.  The answer is: not so much

In theory, the ideal would seem to be as follows.  First boost and clip the signal so that it remains relatively constant for a while, and is capable of providing reasonable treble content.  Though possible to do by simply sticking a fuzz ahead of the pedal, in practice this yields less than ideal envelope detection.  Like any sort of gate, you want detection of the signal envelope to be as early in the signal path as possible.  So, buffer->detect->clip->gain-control->filter.  That is, the signal is tapped at the input buffer, and fed to the rectifier/detector circuitry which will be used to control everything else.  After that tap point, the signal gets seriously boosted and clipped.  Following the boost/clip, two things happen.  First the signal gets variably attenuated to produce the reverse envelope.  Second, the filter gets seriously low-pass filtered to permit fading in of the treble content.

make sense?