I'm having trouble finding an effect that is in my Zoom pedal as a standalone stompbox, more importantly of better quality than the Zoom(the tracking is awful with chords). Its both the slow attack and filter sounds, which produce a volume swell, the latter giving a more subtle envelope filter. Quite similar to the ADSR section of a synth.
I have had a quick look, and the only stompboxes ive ofund this on are the EH microsynth (the attack control), which is far too expensive when i dont want a synth and im not sure if it even effects the raw signal.
perhaps certain envelope filters may have this kind of setting?
i used it mostly for violin like leads, and occasional shoegazer style rhythm.
You might also check for effects labeled "swell." Line6 puts this in some of their stompers. IIRC it is possible to set up the DL4 or the Echo Park delay EFX to do a swell effect (mostly wet mix, lots of swell, single repeat, very short delay). Digitech makes an uber-type wah modeler/foot pedal that very probably does a great swell. It should for nearly a couple humdred bucks.
Or if you want a really good swell with max control, use a volume pedal. Last time I did this at a gig, someone in the audience asked "Where's the violin?"
-=tension & release=-
