If the signal is too low, there's little you can do that will sound any good.
There's an inherent noise floor that's
always there. If you record "silence" and play it back cranked, you'll hear it.
If your signal is large enough the space between the noise floor and the average signal level is large. So the noise is fairly negligible.
If your signal is too small, there's little difference between it and the noise floor. To make it audible then, you have to raise the volume -- which raises the volume of everything, of course, by the same amount. Normalizing will just have the effect of making the noise floor louder by the same amount as your signal, and since they're close in levels, you get a noisy result.
Noise removal tactics work OK for very specific noise sources, like a 60-cycle hum, or the pops and scratches of an LP record... but against generalized noise like this, it will not work miracles.
The
only solution is to get a decent level into the sound card in the first place. If it's too low there are a couple of possibilities:
(1) The level coming out of the tape recorder is not line level. (Maybe the original recording was made with bad levels in the first place? Then you are screwed.) If this is the case, a preamp might help.
(2) The level off the sound card's line in is set too low. DId you adjust this in the Windows mixer? I'm talking about the recording device's input, not the playback device. If that's not clear, read this article:
http://www.cakewalk.com/Support/Lessons/WindowsMixer.htm
If what you have recorded is inherently noisy becuase of low signal-to-noise ratio, there is simply no magic that can make it good as new. "Acceptable", maybe, depending on how forgiving you can be... I mean, people all listened to noisy Victrolas and record players for a long time and though it was great...
