I mix a lot on a radio-broadcast concert series. The Korg Pitchblack is without a doubt the noisiest pedal-tuner I've come across. They seem to really hate the "onespot" power supplies (lots of ground-noise, but then, as far as power supplies go, the onespot is cheap, and they sound cheap). Many times a huge "pop" occurs when you click the on/off switch. I will say that our stage/broadcast is very...closely monitored, so you may not hear these issues in a club or some other venue with a higher noise-floor. Also, maybe this was just an issue with older/well-used models, but I wouldn't recommend them. I like the BOSS TU series just fine for my electric and upright. I really like the sweep mode for daytime/festival stages; I feel like it's easier to see than just the two l3 leds for sharp, flat, in tune. I've heard that many acoustic instruments have issues with the Polytune...there are more overtones, or at least they're more overtones amplified with an acoustic/piezo rig than there are with any magnetic rig (electric or acoustic). But then, that might be complete BS. My theory...