Ok, looks like I made that Swell feature occur using a peak detecting envelope to trigger an ADSR.  The ADSR amplitude modulates the incoming signal before the multitap delay.  I wanted predictable Rise (attack) time, hence the use of the ADSR.  Problem is, I think I tuned this ADSR primarily for the use case of a bunch of taps stacked up, so the sustain and release times are quite short (100 ms). This is the “gating” sound you are hearing.  The audio falls below the trigger threshold and the sustain / release portion is engaged.  I honestly didn’t think of your particular use case.  I agree it would be a nice addition.  

Here’s the rub, if I just go in and increase those times, I’ll probably be messing with lots of peoples’ presets when they update.  Perhaps I could tweak it such that at small numbers of Taps we tie the sustain/release to the rise time or sensitivity?  This would break fewer presets I imagine, but still a significant change…. hmmm… maybe if enough people ask for it, this would be acceptable.  

Interesting. Thanks for digging so deep! Forgive my ignorance… I don’t know how much is involved with really just doing a whole new algorhithm, but wouldn’t that be the way to avoid “breaking” anyone’s existing presets? Volume swells like this are probably more prominently sought after than it seems a lot of company’s might think. Boss’ original pedal sells for a crazy amount if you can find one used and they’ve never re-issued it to my knowledge (Check SG-1 Slow Gear on reverb.com, currently 3 used starting at $425 each). Speaking for myself, I’ve been hanging on to old Boss SE-70s probably mainly for this effect. I use two live, but have six stockpiled. (Would love to replace them all with extra H9’s at some point!) Sent one in for repair to them last year and they said they no longer have mother boards for them. Probably hasn’t been made since ’95 or so (manual is ©1993).  In the modern world it’s also a thread on Line 6’s Helix discussion (they apparently didn’t add it either 😉

If it were possible to make an algorithm featuring this the controls are usually really simple. The SE-70’s just feature a choice of auto/manual (I’m not even sure what manual is.. always use auto), then a sensitivity and a swell which is really the “attack” duration. One of the things that’s great about it is (like this UltraTap seems to do) it sort of stays “open” (no swells) once it inititally swells in, until I guess the input drops below a threshold, then it swells again. Just dreaming aloud here, but IF it were possible to do this, and IF there was extra DSP room (since this doesn’t seem like too much of a strain?) it would be great to couple it with something else too. It seems to usually work best first in a chain, but then maybe followed with… overdrive/fuzz? Then maybe (insert extra H9 I suppose) chorus, delay, verb like Space Time? 

BTW if you search the forum for Slow Gear and Slowgear you’ll find a few other posts about it, including my old one (where someone posted suggestions, but none seem as close as this Ultratap does), and one from Bert Lams (a friend of mine actually and a current H9 user, we tour together and he plays with The California Guitar Trio).

Thanks for the insights! 

Tom