About a certain Jen Repeat Percussion effect...

I have been obsessed with this effect for quite a while now. To me, it always sounded like a tremolo (a tremolo provides modulation of amplitude by means of an LFO with triangle, sine and square wave envelope shapes), but no other tremolo ever got close to the sharpness of this thing. After investigation (mainly putting a sine wave through a Jen pedal and looking at the envelope output with an oscilloscope), it showed its unique shape : A reverse Sawtooth wave with a logarithmic decay illustrating perfectly the aptly named "percussion" effect...

It also showed that a level of dry signal is always present in the mix. That would explain why notes landing near the trough (near silence) can still be heard. Moreover, the circuit impairs a certain color in the form of harmonic distortion but that's another story...

Actual envelope at the output of the Jen (above). Note the logarithmic (non-linear) character of the decays...

Envelope of a perfect reverse sawtooth waveform.

So basically an LFO triggers the gating effect, an ENVELOPE GENERATOR shortens the decay (of what comes through) and a little circuit mixes in a bit of the original dry signal to temper the "tightness" of the effect  ... et voila. Genius 1970's simplicity from a deceased italian company (who apparently ripped it off from Vox who also got the idea from ... and... etc...).
Check the sound of a repeater (skip to around 1m45s in) : Repeat percussion Effect

Pxxxxx