Line6 Bass Pod XT Live: This is a large, comprehensive, digital multi-effects unit with amp modeling, in a floor-board format with many footswitches and an expression pedal. It includes compression modeled on the Urei LA2A, MXR Dynacomp, Boss CS-1, and Line6's own Vetta comp. The MXR, Boss, and Vetta comps occupy one bank of stompbox effect models, of which you can choose only one at a time, using a footswitch labeled "Stomp". The LA2A model is separate, and can be used at the same time as any of the Stomp effects. Any of the comps can be used with any of the amp models.
The LA2A model has only one control, for the amount of compression, while the other three comps have two controls: comp and level. Each of these controls is accessed by double-clicking on either the Stomp or Edit switches, and then hitting one of four buttons to select the parameter to be adjusted, and then using an increment/decrement dial to do the adjusting. It's not the worst system ever, but I prefer real dedicated knobs for each parameter.
Like many other digital comp effects, these models are great for changing your tone, but not so great for utility compression such as peak limiting. They sound good enough for certain flavors and purposes, but I would not recommend them if your main interest was control over signal levels. Many of the amp models sound quite good, and the comp models help to dial in those amp models in either useful or interesting ways. You can also get a cool "heavily compressed" tone by stacking the LA2A with one of the stomp comps. I don't actually think the comp models sound very different from each other though. The LA2A model is darker and the others are brighter, and that's about it. For some unknown reason the difference between models was much more noticeable with their Constrictor pedal.
There is no loss of highs or lows that I could hear, and the noise level is moderately low. There's always a small amount of noise from the different signal processing stages, but it usually was not obnoxious. The effects models are much less "digital sounding" than the Rocktron I reviewed recently, and as noted above, some of the amp models sound really good. Others stank, but that's to be expected when there are dozens of presets.
The footswitches are not true bypass, and I don't think there is an overall "bypass" switch per se. You get your dry signal by individually bypassing the Stomp, Amp, and Mod models, and the dry signal that results is OK but not great. Like most amp-modeling processors, it was designed to provide your complete tone which will be fed into a clean mixer channel or a clean, uncolored power amp; that is why it is not set up like a typical effect to be "on" or "bypassed". The construction seems decently rugged.