I know this is an older thread, but...
I have an NS Designs NXTa that I've been using with my HX Effects (and now the Stomp more recently), and I picked up all three 3Sigma upright IRs last weekend. They seem like a totally worthy purchase, but I've only tried the Hawk IR so far due to being busy with other stuff... and because that's the "jazz" one. lol. Definitely want to check out the other two particularly with bowing!
I was pretty happy with my previous patch that had compression, a smidge of delay (15ms, 35% mix) to somewhat mimic having the upright body, and the 10-band EQ block for some tone shaping (low frequency cut at 31.25Hz and 62.5Hz, and some mid "honk" cut at 250Hz). The Hawk IR seems like quite an improvement, and will almost surely replace my delay/EQ combo when I get a chance to try it out with my jazz combo and an amp.
I haven't had a chance to use them in a live setting, but here's a couple of direct clips for your auditory comparison. I'm pretty happy so far, and I've only tried the Hawk IR (because that's the "jazz" one lol). The IR seems a touch bright at the moment even with the tone knob rolled all the way down, so I may bring the 10-Band EQ block back into play with some high frequency shaping.
The Setup:
NS Designs NXTa with NS Traditional strings > Stomp > PC
Two clips, one dry with just some compression and one using the Hawk IR and compression.
Cheers!
F440
NXTa - Dry.mp3
NXTa - 3Sigma Hawk IR.mp3
