Thank you, Eriksimon, for having such a great grasp of the obvious--of course you can't see my setup. That's kind of the point of the forum and providing system specs, is it not?
And Pancenter, thanks for the link, but the US 1800 works perfectly fine with Garageband and is connected and working perfectly fine with Logic Pro 8, EXCEPT that the audio is coming in muffled. If the guitar cord, the USB cable, or any other wire in the signal chain were loose or not connected correctly, this setup would not function in Garageband, let alone Logic Pro. The software tracks record just fine and the playback of previously recorded audio plays back just fine. Please let me be a little more clear:
1. Logic Pro was installed with the recommended install package and NO additional plug-ins are installed. This is a vanilla setup with no separate hardware other than the US 1800 interface and the electric guitar.
2. The guitar and cable work perfectly in Garageband, but come in muffled in Logic Pro--as though the highs have been rolled off, but not like a guitar tone control roll-off; more like an EQ setting or a low-pass filter. I check my pick-up switch and tone knobs continuously, and the tone knob remains in the full position.
3. I have checked the channel strip and no EQ is involved and no filters of any kind.
4. I have checked and re-checked the Core Audio setup in the Preferences window and the US 1800 is the Device selected (remember that in LP8, there is no differentiation between Input and Output Device in LP8 Preferences as there is in Garageband).
5. This behavior is consistent in both channels 8 and 9 (the guitar inputs for the US 1800), and presents itself when adding a DI box between the guitar and the US 1800.
6. I asked the Logic Pro guru at Guitar Center yesterday before I posted here and he suggested that there may be a sample rate conflict but had no idea how that could be remedied.
7. I tried recording this guitar with this input problem using Guitar Amp Pro and ended up having to EQ the crap out of the track to even get it close to a decent guitar sound. Thankfully, the track used heavy distortion and the tone was not critical to the success of the whole recording. If it had to be clean guitar, the track would have been unusable.
So, hopefully this info will help to clarify the situation; but, I'm baffled. The muffled-ness makes no sense to me. Anyone have any ideas?
Thanks!