The Avisoft web pages include a tutorial that helps explain what the recorder
preamp noise specifications mean.
Consider these specifications only:
Olympus LS-11 -122dBu unweighted
Olympus LS-7 -118dBu unweighted
This means the LS-11 preamp is 3dBu quieter than the LS-7 under these test
conditions. That's a difference that you will be able to hear in your
recordings, but only if you use an external mic that has very low self noise,
and when recording in a space that has a very quiet ambience. If you're
recording louder sounds, or using a mic with more self noise, the recorder self
noise will be masked under most circumstances.
Results from pocket recorders almost always can be improved by the use of a
good quality external microphone. For example, Klas Strandberg has introduced
a model designed for the Olympus LS-xx models. http://www.telinga.com/ls10.htm
Unfortunately, you'll need to spend quite a bit more than the cost of the
recorder on such a microphone.
For the record, neither the LS-11 nor the LS-7 is considered a good solution by
itself as a primary field recorder. These are pocket-size models that best
serve as casual recorders note-taking machines. They can be pressed into
service as a primary recorder when you want to travel light, or need a less
obtrusive recording kit.
If you're looking to make very high quality recordings, none of the pocket
recorders is a good solution. In the less-than-$1000 range, take a look at the
Fostex FR-2LE recorder. And expect to pay an additional $1000 to $2000 for
microphones, cables, wind screens and mic stands. Professional gear costs a
lot, but delivers superior results, increased durability, and improved ease of
use under difficult conditions.
Does this mean you can't make an excellent recording with an inexpensive pocket
recorder? No, but the conditions have to be just right.
Many vendors of recording equipment will allow you to try out a recorder for a
few days to see if meets your requirements. Try several models to see which
one works best for you.